Deep-sea benthic hydroids (Cnidaria, Hydrozoa) from Antarctic submarine ridges off the Ross Sea (Antarctica)

Deep-sea benthic hydroids (Cnidaria, Hydrozoa) from Antarctic submarine ridges off the Ross Sea (Antarctica) | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Deep-sea benthic hydroids (Cnidaria, Hydrozoa) from Antarctic submarine ridges off the Ross Sea (Antarctica) Álvaro Luis Peña Cantero This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4679741/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 26 Sep, 2024 Read the published version in Polar Biology → Version 1 posted 9 You are reading this latest preprint version Abstract Knowledge of benthic hydroids inhabiting the Antarctic continental shelf waters, particularly of relatively well-studied areas, has increased in recent years. This has allowed us to recognise them as one of the main and most characteristic zoological groups of the Antarctic benthos. However, little is known about the hydroids dwelling on the continental slope or deeper waters, let alone on bottoms away from the Antarctic continent, despite the fact that the Southern Ocean extends significantly norhwards. This study contributes to reducing that knowledge gap by studying material collected from a series of deep-sea ridges north of the Ross Sea, from which hydrozoans have never been reported. Twelve species, including Halecium divergens sp. nov., have been found and studied. Except for Turritopsis sp., belonging to the Anthoathecata family Oceaniidae, all species belong to Leptothecata, in particular to the families Campanulariidae, Haleciidae, Lafoeidae, Phylactothecidae, Sertularellidae and Symplectoscyphidae. Lafoeidae is the most represented family with four species. Sertularella pseudovervoorti and Filellum liberum are found for the second time. The discovery of Symplectoscyphus frondosus , a species previously considered endemic to the shelf and slope of the eastern Ross Sea, significantly extends its known northern distribution limit. Tulpa diverticulata and the genus Tulpa are reported in Antarctic waters for the first time. The lower limit of the bathymetric range for several species has been extended. Despite being well within Antarctic waters, the studied area hosts a very distinctive fauna, markedly different from the typical Antarctic benthic hydroid fauna. Its endemisms, the presence of species unknown in the Antarctic region and the absence of representatives of the most characteristic Antarctic genera account for its originality. Hydrozoans Biodiversity New species New records Biogeography Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Introduction While we have acquired considerable knowledge of the Antarctic benthic hydroid fauna inhabiting the continental shelf waters, particularly in relatively well-studied areas, such as the Weddell Sea (Soto Àngel and Peña Cantero 2019 ) and the Ross Sea (Peña Cantero 2017 ; 2019 ; 2023 ), little is known about the hydrozoan fauna dwelling on the continental slope or in deeper waters, except for a few exceptions (e.g. Peña Cantero 2012 ; 2019 ). Additionally, despite the Southern Ocean extending significantly norhwards, studies have usually been conducted in waters close to the continent or the few islands surrounding it, such as the Balleny Islands (Peña Cantero 2009 ; 2021 ), Peter I Island (Peña Cantero 2010 ) or Scott Island (Peña Cantero 2019 ). In fact, apart from Peña Cantero’s ( 2019 ) study, which focused on hydroids from the Ross Sea, but also from the remote Scott Island area, no hydroids have been studied from bottoms away from the Antarctic continent or its surrounding islands. I present here the results of a study on a small collection of benthic hydroids from deep waters off the Ross Sea, collected during several New Zealand research surveys. Much of the value of this study lies in its focus on deep-water habitats of the Southern Ocean located far from the Antarctic continent, which, as mentioned before, are practically unexplored for benthic hydroids. On the other hand, while the boundaries of the Southern Ocean are well defined for the pelagos by the Polar Front, they are less clear for the benthos (Picken 1985 ). Studies like this will contribute to defining those boundaries. Material and methods The material studied was collected during the New Zealand TAN1802 scientific survey, conducted on board the R/V Tangaroa , and operations of fishing vessels under the New Zealand Scientific Observer Programme (TRIP2993 and TRIP2996). The samples studied here were gathered using an epibenthic sledge and bottom longlines from a series of submarine ridges north of the Ross Sea (Fig. 1 ), at depths between 652 and 1770 m (Table 1 ). Hydrozoans were preserved in 70% ethanol. Table 1 Station data Station Date Latitude (S) Longitude (W) Depth (m) Gear TAN1802/186 08/03/2018 66.7448 − 66.7467 177.093 652 − 654 Epibenthic sled TRIP2993/11 07/12/2009 64.5541 171.2308 1533 Bottom longline TRIP2993/20 11/12/2009 64.5716 − 64.59 171.1216 − 171.2216 1770 − 1541 Bottom longline TRIP2996/1 05/12/2009 65.5441 175.7558 1637 Bottom longline The material studied here is deposited in the National Institute of Water and Atmospheric Research Invertebrate Collection at Wellington (NIWA), New Zealand. Results Species account Oceaniidae Eschscholtz, 1829 Turritopsis sp. (Fig. 2) Material examined. TAN 1802/186 , a few stems up to 5 mm high, on a bryozoan. Description. Hydrorhiza stolonal, creeping on bryozoan, giving rise to unbranched, erect stems up to 5 mm high, each with a single distal polyp. Stem covered with firm double-layered perisarc (Fig. 2a); outer layer not reaching pedicel end (Fig. 2b). Hydranth 350–400 µm high, 200 µm in maximum diameter, with about 12 filiform tentacles at different levels (Fig. 2c-e). Cnidome (Fig. 2f-h) consisting of microbasic euryteles (8.6±0.4 x 5.0±0.2 µm, range 8-9 x 4.5-5 µm) and desmonemes (5.5 x 3.5 µm). Remarks. The material is infertile, and only a few poorly preserved polyps are present, preventing a complete characterization and identification of the species. The only material from Antarctic waters so far assigned to the genus Turritopsis is that described by Peña Cantero et al. (2013), which is also based on infertile material. The material studied here differs by having unbranched stems, but this could be related to the smaller size of the stems (up to 5 mm high here and up to 15 mm in the material studied by Peña Cantero et al. 2013). These authors indicated that Stepanjants’ (1979) material of Corydendrium could actually belong to Turritopsis . Ecology and distribution. The material studied by Peña Cantero et al. (2013) was collected at a depth of 20 m from Tethys Bay, in the Ross Sea. Present material comes from much deeper waters (652–654 m). Family Lafoeidae Hincks, 1868 Acryptolaria frigida Peña Cantero, 2014 (Fig. 3a) Material examined. TAN1802/186 , three stems 150, 150 and 130 mm high, one of them with coppinia, basibiont of Lafoea dumosa . Description. Polysiphonic stem up to 150 mm high. Branching alternate, almost in one plane, usually every third hydrotheca; branches up to third order observed. Hydrothecae alternately arranged approximately in one plane. Hydrotheca markedly curved abcaudally (Fig. 3a), tubular, cylindrical at free part, smoothly tapering basally at adnate portion. Hydrotheca adnate to internode for about two- thirds of its length. Adcauline wall strongly convex. Abcauline wall concave, especially at distal half. Hydrothecal aperture circular, directed outwards. Rim even, sometimes with a few short renovations. Coppinia without defensive tubes; gonothecae distally broken. Measurements (in µm). Hydrothecae : abcauline wall 1450–1650, free part of adcauline wall 380–810, adnate part of adcauline wall 1200–1350, adcauline wall 1730–2010, diameter at aperture 280. Cnidome : larger microbasic mastigophores 20.0±0.6 x 6.8±0.4 (n=10), range 19.0–20.5 x 6.5–7.5 µm. Remarks. The material studied perfectly matches previous descriptions of the species in both the shape and size of the hydrotheca and the cnidome. Ecology and distribution. Acryptolaria frigida is known from depths between 85 (Peña Cantero 2010) and 728 m (Peña Cantero 2014); present material at a depth of 652−654 m. Coppiniae in March. Circum-Antarctic distribution (Peña Cantero 2014). It has been reported from the Weddell Sea (Peña Cantero et al. 2004; Soto Àngel and Peña Cantero 2019; Peña Cantero 2020), off Peter I Island (Peña Cantero 2010) and from the Bellingshausen Sea (Peña Cantero 2012), in West Antarctica, and off Queen Mary Coast (Peña Cantero 2014), in East Antarctica. Present material represents the first record for this sector of the Antarctic region. Filellum liberum Peña Cantero, 2024 (Fig. 3b-d) Material examined. TRIP2993/20 , several hydrothecae, on axis of dead gorgonian, with coppinia. Description. Stolonal colony consisting of stolons creeping on a gorgonian axis, giving rise to erect, tubiform, completely free hydrothecae (Fig. 3b-c) of highly variable shape and size (up to 770 µm high). Hydrothecal diameter clearly increasing distally from origin; hydrothecal aperture circular (120–150 µm in diameter), rim even, slightly flared, frequently with several renovations of variable length (Fig. 3b-c). Coppinia consisting of tightly packed gonothecae surrounded by a fence of protective tubes arching over them, creating a protective brooding chamber. Defensive tubes unforked, distally open, and basally partially coalescent. Gonothecae flask-shaped, with a circular aperture on a short distal neck, distally flared (Fig. 3d). Remarks. The present material perfectly agrees with the orginal description of both the hydrothecae and the coppinia. The species is characterised by having completely free hydrothecae. Ecology and distribution. Filellum liberum seems to be a deep-water species. It was known from depths between 505 and 1064 m (Waston 2003 as Lafoea tenellula Allman, 1877, see Peña Cantero 2024); present material collected at depths between 1541 and 1770 m, distinctly increasing its lower bathymetric limit. Coppiniae are known in January (Watson 2003), April (Peña Cantero 2024) and December (present study). Filellum liberum is known only from waters around Macquarie Island (Peña Cantero 2024) and the Long Ridge area (present study). Lafoea dumosa (Fleming, 1820) (Fig. 3e) Material examined. TAN1802/186 , a few stems up to 15 mm high, on A. frigida . Description. Monosiphonic stems up to 12 mm high, unbranched, with up to 15 hydrothecae alternately arranged in two planes, forming an acute angle. Two polysiphonic stems also present, 16 and 10 mm high, with five and two primary branches, respectively. Branches originating from accessory tubes. Hydrothecae straight (Fig. 3e), mostly cylindrical, tapering at their basal third into a twisted pedicel. Hydrothecal aperture circular; rim even. Measurements (in µm). Hydrotheca : height from ring of desmocytes 550–630, pedicel 200–250, diameter at aperture 160–200. Total length (hydrotheca plus pedicel) : 750–880. Cnidome : isorhizas 20.4±0.8 x 10.6±0.7 (n=5), range 19.0–21.0 x 10.0–11.5. Ecology and distribution. In Antarctic waters, Lafoea dumosa is known from depths between 12 (Stepanjants 1979) and 1157 m (Peña Cantero 2014); present material at a depth of 652–654 m. Cosmopolitan distribution (Stepanjants 1979). In the region, reported from the Ross Sea (Totton 1930; Peña Cantero 2017, 2023) and the Balleny Islands (Peña Cantero 2021). Lafoea sp. (Fig. 3f-g) Material examined. TRIP2993/20 , several stems up to 13 mm high, on axis of a dead gorgonian and Halecium divergens sp. nov. Description. Stems up to 13 mm high, either monosiphonic or polysiphonic. Branching present only on polysiphonic stems; branches originating from accessory tubes. Hydrothecae alternately arranged in two planes, forming an acute angle. Hydrothecae typically curved abcaudally (Fig. 3f), relatively long and thin, cylindrical for most of their length, tapering only at their basal fourth into a twisted pedicel. Hydrothecal aperture circular; rim even, usually with numerous renovations (up to ten observed). Measurements (in µm). Hydrotheca : height 450–500, diameter at aperture 80–120. Total length (hydrotheca plus pedicel) : 600. Cnidome : microbasic mastigophores 6–6.5 x 2.5–3. Remarks. There are also stolonal hydrothecae, on both Halecium divergens sp. nov. and the gorgonian axis. The present material is clearly different from L. dumosa , both in the shape and size of the hydrotheca (e.g. 160–200 µm in diameter at the aperture in the material of L. dumosa studied here), as well as in the cnidome. After several attempts to study the cnidome of this species, I have been unable to find the large isorhizas characterising L. dumosa (Schuchert 2001). Only small microbasic mastigophores were found (Fig. 3g). Although I could not observe them discharged, I did find a broken nematocyst exposing a short, isometric shaft (Fig. 3g). The scarcity of the available material and the absence of coppinia prevent me from fully characterising this species. Ecology and distribution. Lafoea sp. was collected at depths between 1541 and 1770 m, epibiotic on the axis of a gorgonian and on H. divergens sp. nov. Family Campanulariidae Johnston, 1836 Tulpa diverticulata Totton, 1930 (Fig. 3h) Material examined. TAN 1802/186 , several stems up to 60 mm, on axis of dead gorgonian, basibiont of Symplectoscyphus nesioticus . Description. Stems up to 60 mm high, monosiphonic, with alternate hydrothecae in an almost unilateral arrangement. Hydrothecae on pedicels of variable length, frequently with regenerations. Hydrotheca tubular (Fig. 3h), with diameter increasing from diaphragm to basal third, then slightly decreasing to distal third, and finally widening again to aperture. Rim of hydrothecal aperture even, but everted and sinuous. Hydrothecal wall with more or less marked facets, fading basally. A few short renovations of hydrothecal rim might be present. Hydrotheca with distal diverticulae (Fig. 3h). Measurements (in µm). Stolon : diameter 380. Pedicel : length 1800–4000. Hydrotheca : height 2900–3400, diameter at aperture 1000–1300. Remarks. There are a few records of the species, but most of them are dubious because the peculiar diverticulae characterising this species (Totton 1930) were neither described nor depicted; only Ralph (1957) noted their presence in her material. Ecology and distribution. Tulpa diverticulata is known for sure from a depth of 456 m (Totton 1930); present material collected at a depth of 652−654 m. The species is certainly present in New Zealand waters (Totton 1930; Ralph 1957). Symplectoscyphidae Maronna, Miranda, Peña Cantero, Barbeitos and Marques, 2016 Symplectoscyphus frondosus Peña Cantero, 2010 (Fig. 4a) Material examined. TRIP 2996/1 , one stem 100 mm high, broken into three main fragments, on coral. Description. Stem erect, 100 mm high, rigid, markedly tortuous, strongly polysiphonic (diameter at basal part 3 mm). Branches more or less perpendicular to long axis of stem, strongly polysiphonic over great extent, tightly packed, and approximately of similar development, giving stem a bottlebrush appearance. Primary branches spirally arranged, completing a turn every five branches. Branches and stems divided into short internodes by alternating oblique nodes, each internode with one hydrotheca. Hydrothecae alternately arranged in approximately one plane, densely packed, with distal part of each hydrotheca clearly overlapping basal part of following one (Fig. 4a). Hydrotheca slightly curved abcaudally. Adcauline wall adnate to internode for about half its length; free part of adcauline wall slightly convex or straight. Abcauline wall slightly convex basally and slightly concave distally. Rim of hydrothecal aperture with three cusps separated by deep embayments. Hydrothecal diameter distinctly decreasing towards aperture. Measurements (in µm). Hydrotheca : abcauline wall 360–400, free part of adcauline wall 210–260, adnate part of adcauline wall 210–270, adcauline wall 420–500, diameter at aperture 110–130, maximum diameter 150, diameter at base 110. Ecology and distribution. Shelf and slope species, known from depths between 321 and 2283 m (Peña Cantero 2019); present material collected at a depth of 1637 m. Previously considered endemic to the eastern Ross Sea (Peña Cantero 2017, 2019), the present material, outside the typical area, represents its northernmost recorded occurence. Symplectoscyphus nesioticus Blanco, 1977 (Fig. 4b) Material examined. TAN 1802/186 , a few stems up to 10 mm high, on T. diverticulata and axis of a dead gorgonian. Description. Monosiphonic, unbranched stems up to 10 mm high and nine hydrothecae. Stem internodes in marked zigzag, each with a distal hydrotheca. Hydrotheca tubular, free for most of its adcauline wall (Fig. 4b); free part of adcauline wall slightly convex. Hydrotheca usually with distinct inflexion point where adcauline wall becomes free. Abcauline wall slightly concave. Hydrothecal aperture with three sharp cusps separated by deep embayments. Hydrothecal diameter usually increasing distally. Measurements (in µm). Hydrotheca : abcauline wall 370–430, free part of adcauline wall 230–400, adnate part of adcauline wall 80–100, adcauline wall 310, diameter at aperture 180–200. Ecology and distribution. Shelf species (Peña Cantero 2017), collected at depths from 56 (Peña Cantero 2006) to 701 m (Peña Cantero 2014); present material found at a depth of 652–654 m. Circum-Antarctic distribution (Peña Cantero 2014). In the region, known from the Ross Sea (Peña Cantero 2017) and from a seamount of the nearby Scott Island (Peña Cantero 2019). Haleciidae Hincks, 1868 Halecium divergens sp. nov. (Figs 5–6) Material examined. TRIP 2993/20 , several stems up to 10 mm high, with gonothecae, on axis of dead gorgonian (Holotype, NIWA 131355). Description.Monosiphonic stems, up to 10 mm high, arising from stolons creeping on axis of dead gorgonian. Stems resting on stolonal apophyses (Fig. 5a–b), sometimes followed by an athecate internode (Fig. 5b). First hydrothecate internode either ‘typical’ (Fig. 5b) with distal hydrotheca and apophysis supporting successive internode, or without apophysis and first regular internode originating within distal hydrotheca (Figs 5a, 6b). Successive typical internodes in marked zigzag (Fig. 6a) (angle about 70°) and resting on strong apophysis originating from below hydrotheca (Fig. 5a–b). New branches originating from hydrophores of lower-order hydrothecae. Distance between hydrotheca and apophyses small (Fig. 6b-d), resulting in a free and very short hydrophore. Internodes usually very long, with a basal swelling. Hydrothecae alternately arranged in one plane (Fig. 6a), placed at end of a short, free hydrophore (Figs 5a–c, 6b–c); ratio between adcauline length of hydrophore and diameter at diaphragm 0.2–0.5. Without pseudodiaphragm, but sometimes with thin perisarc projection on adcauline side of hydrophore (Fig. 5b). Hydrothecae usually at level of basal node of following internode (Figs 5a–b, 6b–d), relatively high, strongly widening distally (Figs 5a–c, 6b–d), with everted rim (Fig. 6d) and ring of desmocytes above diaphragm. Up to third-order hydrothecae observed on long and smooth hydrophores. Gonothecae extremely flat and concave (spoon-shaped), with distal aperture, resting on a short pedicel originating directly from stolon (Fig. 6e). Putative male gonotheca roughly rounded (Figs 5e, 6g). Putative female gonotheca larger (Figs 5d, 6e), with distinctly longer pedicel, two basal lobes, and aperture forming a sort of embayment (Figs 5d, 6f). Measurements (in µm). Stolonal apophyses : length 100-150 (350), width 110–140. Internodes : length 1400–1800 (up to hydrothecal diaphragm), wide 120–150. Hydrothecae : height 60–90, diameter at aperture 210–270, diameter at diaphragm 150–170. Adcauline length of hydrophore : 30–50. Lower-order hydrophore : length up to 950. Female gonothecae : height 1450, width 1100, aperture 200. Male gonotheca : height 1000, width 870, aperture 190. Cnidome : microbasic euryteles 10–11 x 4.5–5.5 and microbasic mastigophores 7.5 x 2. Remarks.The extreme flatness of the gonothecae is likely due to the fact that they have already shed their contents. On one occasion, a gonotheca was found originating from below the hydrotheca of the first stem internode; the rest of the many gonothecae present in the studied material arise directly from the stolons. As mentioned earlier, there are two types of stems based on the structure of the first internode. Some stems begin with a regular internode that includes a distal hydrotheca and an apophysis below it supporting the following internode (Fig. 5b). In contrast, other stems start with an internode that has a distal hydrotheca but lacks an apophysis. In this case, the next internode originates from the hydrophore of a lower-order hydrotheca, typically a secondary hydrotheca (Fig. 5a), although it may also originate from an even lower-order hydrotheca. The species has free hydrophores, a feature shared with a group of other Antarctic species of Halecium ( H. antarcticum Vanhöffen, 1910, H. banzare Watson, 2008, H. exaggeratum Peña Cantero, Boero and Piraino, 2013, H. frigidum Peña Cantero, 2010, H. interpolatum Ritchie, 1907, H. pallens Jäderholm, 1904 and H. pseudodelicatulum Peña Cantero, 2014). However, it differs from all these species because the hydrophore is distinctly much shorter. The closest species in this feature is H. interpolatum , although that length is still significantly longer in Ritchie’s species; the ratio between the adcauline length of the hydrophore and the diameter at the diaphragm is around 0.8–0.9 in H. interporlatum , but only 0.2–0.5 in the present species. By the size and general shape of the hydrotheca it is also closest to H. interpolatum . However, they differ in colony and internode structure. In Ritchie’s species, the stems, basally polysiphonic and slightly geniculate, give rise to paired branches originating from the hydrophore of a primary hydrotheca. Halecium interpolatum is also distinctive in the shape of the internodes, which have a long and straight basal part followed by one or two annulations. Neither of those features are found in the present species. Finally, while the gonothecae develop from within the hydrotheca in H. interpolatum , in the present species, as mentioned earlier, they arise from the stolons. Ecology and distribution. Halecium divergens sp. nov. was collected at depths between 1541 and 1770 m, on the axis of a dead gorgonian. Gonothecae in December. Etymology. The specific name divergens makes reference to the marked different directions taken by the successive internodes. From New Latin divergens. Halecium jaederholmi Vervoort, 1972 (Fig. 7) Material examined. TRIP 2993/11 , a few stems up to 60 mm high, with one female gonotheca, on axis of a dead gorgonian. Description. Stems up to 60 mm high, honey-coloured, polysiphonic and branched. Branching irregular, sometimes branches almost unilateral and nearly perpendicular to plane of hydrothecae. Branches resting on large apophysis originating from hydrophore of a hydrotheca, usually on one lateral, although closer to abcauline side. Typically, one ahydrothecate internode after apophysis (Fig. 7a), sometimes more (Fig. 7b). Occasionally, branches originating from inside a hydrotheca. Stem and branches divided into internodes by slightly oblique alternating nodes; one hydrotheca per internode. Hydrothecae arranged alternately in two planes, forming an angle of about 70°. Primary hydrothecae resting on sessile hydrophores (Fig. 7a–c). Adcauline hydrothecal wall much more developed than abcauline one and completely adnate to internode (Fig. 7a, c–d), frequently extending to distal node (Fig. 7d). Hydrothecal aperture slightly directed downwards (Fig. 7b). One secondary hydrotheca sometimes present, not resting on a hydrophore and, therefore, practically within primary hydrotheca. Secondary hydrotheca approximately equally developed all around. Female gonotheca kidney-shaped (Fig. 7e), with two hydrothecae at the concave side. Measurements (in m). Internode : length 750–1000, wide 150–180. Hydrothecae : height 30–40, diameter at aperture 180–190, diameter at diaphragm 160–180. Hydrophore : adcauline length 120–150. Gonotheca : height 1500, maximum diameter 600. Cnidome : microbasic euryteles 11.0±0.7 x 5.1±0.2 (n= 10), range 10–12 x 5.0–5.5, microbasic mastigophore 7.5 x 3. Remarks. There is usually an ahydrothecate internode after the apophyses supporting the branches, although there may be even more (up to eight have been observed). However, this seems to be related to fractures. In fact, ahydrothecate internodes may also be found along the branches, clearly indicating that they formed following a fracture. Ecology and distribution.Shelf and slope species, collected at depths from 24 (Vervoort 1972) to 950 m (Peña Cantero 2019); present material found at a depth of 1533 m, extending significantly its lower bathymetric limit.Gonotheca in December. Pan-Antarctic distribution (Peña Cantero 2014). In the region, reported from the Ross Sea (Peña Cantero 2017) and from seamounts of the nearby Scott Island (Peña Cantero 2019). Family Sertularellidae Maronna, Miranda, Peña Cantero, Barbeitos and Marques, 2016 Sertularella pseudovervoorti Peña Cantero, 2019 (Fig. 4c–f) Material examined. TRIP 2993/20 , a few stems up to 10 mm high, on axis of a dead gorgonian. Description. Monosiphonic stems up to 10 mm high and five hydrothecae, unbranched or scarcely branched (up to second-order branches present). Branches originating below a hydrotheca (Fig. 4c–e). Stem divided into relatively long and thin internodes by slightly marked, alternating, oblique nodes. Internodes arranged in a marked zigzag pattern. First stem internode much longer. Hydrotheca cylindrical, practically straight, free for most of its adcauline length (Fig. 4c–f). Maximum diameter distinctly above adnate part; diameter slightly decreasing distally and more markedly basally. Abcauline wall either approximately straight or slightly convex basally and concave distally. Free part of adcauline wall slightly convex, with three or four slight undulations; adnate part practically straight. With distinct inflexion point between free and adnate parts of adcauline wall. Rim of hydrothecal aperture with four small, equally developed cusps, separated by shallow embayments. Measurements (in μm): Internodes : length 1220–4400 (first internode 2600–4400), diameter at hydrothecal base 170–200. Hydrothecae : length of abcauline wall 500–550, free part of adcauline wall 320–450, adnate part of adcauline wall 150–250, adcauline wall 550–640, diameter at aperture 190–250, maximum diameter 230–290. Remarks. The stems are either unbranched or scarcely branched. Only four stems are branched, usually having one or two primary branches; only one stem has a second-order branch. This particular stem, approximately 8 mm high, has a primary branch originating below its fourth hydrotheca. This primary branch, in turn, gives rise to an incipient secondary branch at its third hydrotheca, which has not yet formed a hydrotheca. The position of the primary branch is variable; it has been observed at the first, second, fourth, or fifth hydrotheca in different stems. The main axis of the stems has up to five hydrothecae, although some of the branched stems have up to eight hydrothecae in total. The first internode is distinctly longer than the remaining stem internodes, their length decreasing distally; for instance, in one stem, the length of the first four internodes was 4400, 2100, 1420 and 1220 µm, respectively. The colony structure and the shape of the hydrotheca in the studied material perfectly agree with the type material of S. pseudovervoorti , although the hydrothecae are distinctly smaller. However, this difference could be attributed to intraspecific variation. It is important to note that knowledge of this species is based on very limited material. Sertularella pseudovervoorti was previously known only from the original description, which was based on a few stems up to 15 mm high. Consequently, I am considering the present material as belonging to S. pseudovervoorti , which, in addition, was discovered in the nearby Scott Island area. Ecology and distribution. Sertularella pseudovervoorti was previously known from depths between 1520 and 1560 m (Peña Cantero 2019); present material collected between 1541 and 1770 m, slightly increasing its lower bathymetric limit. It has been found growing on the axis of dead gorgonians (Peña Cantero 2019; present material). This represents the second record of the species. It was previously known only from a seamount off Scott Island (Peña Cantero 2019). Phylactothecidae Stechow, 1921 Hydrodendron arboreum (Allman, 1888) (Fig. 4g–h) Material examined. TAN 1802/186 , three stems up to 50 mm, on axis of gorgonian. Description. Stems polysiphonic, up to 50 mm high, branched. Branching in one plane, in subopposite pairs. Only primary branches present, monosiphonic. Stem and branches divided into relatively long internodes bearing one hydrotheca each. Hydrothecae alternately arranged in one plane. Hydrotheca on a short hydrophore provided with a distinct free part (Fig. 4g). Hydrothecae completely free (Fig. 4g), low, with a ring of desmocytes between diaphragm and aperture; abcauline and adcauline wall straight, the former slightly abcaudally directed. Hydrothecal diameter barely increasing distally. Hydrothecal aperture circular, markedly tilted abcaudally; rim even. Lower-order hydrothecae (up to fourth-order observed) usually present (Fig. 4g), on short hydrophores, with a ring of desmocytes, and a circular aperture (rim slightly everted); hydrothecal diameter distinctly increasing distally. Typically, one nematophore per internode, on opposite side of hydrotheca, but an extra nematophore also common on abcauline side of primary hydrophore (Fig. 4g). Nematophores provided with small cone-shaped nematotheca with desmocytes (Fig. 4h). Measurements (in m). Internode : length 840–1500, diameter at distal node 180–210. Hydrothecae : height 20–30, diameter at aperture 210–240, diameter at diaphragm 200–230. Hydrophore : adnate part 230–240, free part 20–70. Nematotheca : height 60–80, diameter at aperture 75–80. Remarks. All the stems are polysiphonic, although they are provided with a significant monosiphonic distal part. The stems are also branched, except for the smallest. The branches are typically monosiphonic, although one branch has a small basal portion with incipient polysiphony. Branching appears to occur in subopposite pairs, which is evident in the most developed stem. This stem has six primary branches arranged in three subopposite pairs. Ecology and distribution. Eurybathic species found at depths from 18 (Hickson and Gravely 1907) to 1370 m (Peña Cantero and Ramil 2006); present material collected at a depth of 652−654 m. Pan-Antarctic distribution (Peña Cantero and Ramil 2006). In the region, frequently reported from the Ross Sea (cf. Peña Cantero 2017) and once from the Balleny Islands (Peña Cantero 2009). Discussion Biodiversity As shown above, 12 species were found in the studied collection, gathered from an Antarctic area where knowledge of benthic hydroids was non-existent. Among the material examined, only one species of Anthoathecata was present, belonging to the family Oceaniidae. The remaining hydroids belong to Leptothecata, with Lafoeidae being the most diverse family, represented by four species. Haleciidae and Symplectoscyphidae each have two species, while the families Campanulariidae, Phylactothecidae and Sertularellidae are each represented by one species. The occurrence of species in this study is extremely low as all of them were present at only one station. The station with the highest species diversity was TAN1802/186 with six species, followed by TRIP2993/20 with four. Only one species was found at each of the other two stations (TRIP2996/1 and TRIP2993/11). This variation could be related to the sampling gear employed; at the station with the highest species diversity, samples were collected using an epibenthic sledge, whereas the other samples were obtained using bottom longlines. The relatively high species diversity in sample TRIP2993/20, compared to the other samples obtained with bottom longlines, is clearly related to the fact that the species were growing on the axis of a gorgonian. Depth could also play a role in the species richness observed. The bottoms sampled in TAN1802/186 are distincly shallower (652–654 m) than those from the remaining samples: TRIP2993/11 (1533 m), TRIP2993/20 (1541–1770 m) and TRIP2996/1 (1637 m). TAN1802/186 is also the closest station to the Antarctic continent. A comparision of the benthic hydroid species diversity found in the studied collection with that present in the neighbouring areas (the Ross Sea, the Balleny Islands and the Scott Island area) (Fig. 1 ) shows that it is much lower than in the Ross Sea, where a total of 84 species have been reported, making it the third region with the highest number of benthic hydroids among the larger Antarctic areas (Peña Cantero 2023 ). The much higher diversity in the Ross Sea can partially be explained by the high number of samples containing hydroids (more than a hundred) studied from that region, as well as by the wide bathymetric range surveyed, extending from the tidal level to depths of the continental slope (up to 1865 m). The species richness is also significant lower than that of the Balleny Islands, where a total of 34 species are known (Peña Cantero 2021 ). As with the Ross Sea, a larger number of samples (about thirty) have been studied from the Balleny Islands, and the bathymetric range surveyed (63 to 702 m) covers shallower bottoms. Regarding the Scott Island area, the species diversity is however similar [11 species are known (Peña Cantero 2019 )], despite the fact that the number of samples studied, coming from a similar bathymetric range (300 to 1560 m), is significantly higher (15 samples compared to four here). Biogeography From a biogeographical perspective, it is worth mentioning the case of S. frondosus . This species is relatively abundant in the shelf and slope of the eastern Ross Sea (Peña Cantero 2017 , 2019 ). Its absence from the nearby areas of the Balleny Islands (Peña Cantero 2009 , 2021 ) and Scott Island (Peña Cantero 2019 ), previously prompted me to consider it to be endemic to the eastern Ross Sea (Peña Cantero 2019 ). However, the present study has demonstrated that its known distribution extends much further north (Fig. 8 ). In the opposite direction we find the case of T. diverticulata and the genus Tulpa , never before reported in the Southern Ocean. Tulpa diverticulata was originally described from New Zealand (Totton 1930 ), and there have been a few unconfirmed or doubtful records in sub-Antarctic waters, but none in Antarctic waters. As for the genus, the closest record to Antarctic waters is for Tulpa tulipifera (Allman, 1888) from the sub-Antarctic Burdwood Bank (El Beshbeeshy 2011 ; Soto Àngel and Peña Cantero, 2015 ). The discovery of T. diverticulata in the present study, at almost 67°S, confirms the presence of this species, and the genus Tulpa , well within waters of the Southern Ocean. It is also worth mentioning the discovery of the newly described F. liberum , previously known only from the vicinity of Macquarie Island (Peña Cantero 2024 ). Together with T. diverticulata , this species is a clear example of the biogeographic links between the Southern Ocean and the sub-Antarctic Macquarie Ridge and New Zealand. Concerning the faunistic relationships of the study area with neighbouring regions (Fig. 1 ), among the eleven species known from the remote Scott Island area (Peña Cantero 2019 ), three are present in the studied collection ( H. jaederholmi , S. pseudovervoorti and S. nesioticus ). Halecium jaederhomi and S. nesioticus are also found in Antarctic continental shelf waters, but S. pseudovervoorti is known only from the Scott Island area and the area studied here, suggesting it may be endemic to this part of the Southern Ocean. Relationships with the Balleny Islands are weaker, with only two out of the 34 species known from that area (Peña Cantero 2021 ) present in the studied collection: L. dumosa , which has a worldwide distribution, and H. arboreum , widely reported in Antarctic and sub-Antarctic waters. Finally, of the 84 species known from the Ross Sea, only five are present in the studied collection: L. dumosa (cosmopolitan distribution), H. jaederholmi and H. arboreum (Pan-Antarctic distribution), S. nesioticus (circum-Antarctic distribution), and S. frondosus , previously considered endemic to the eastern Ross Sea. In general, while acknowledging the limitations in drawing general conclusions due to our limited knowledge of hydroid diversity in the studied area, the fauna inhabiting these waters cannot be considered a typical Antarctic fauna. Several reasons support this assertion. First, the presence of endemic species ( H. divergens sp. nov., known only from the study area, and S. pseudovervoorti , found exclusively here and in the nearby Scott Island area). Second, the presence of species unknown from the Antarctic region (i.e., F. liberum and T. diverticulata ). Finally, the complete absence of representatives from the most characteristic genera of Antarctic benthic hydroids: Antarctoscyphus , Oswaldella , Schizotricha and Staurotheca . These four genera, along with Halecium and Symplectoscyphus , account for about 75% of the Leptothecata species diversity in the Antarctic (Peña Cantero 2014b). The last two genera, which are represented in the studied collection by two species each, have a much broader distribution and are extensively represented outside the Antarctic region. Declarations Competing interests The author declares no competing interests Conflict of interest The author declares that there is no conflict of interest. Author contribution The author carried out all aspects of the present study. Acknowledgements I want to express my gratitude to the NIWA Invertebrate Collection, Sadie Mills, Di Tracey, and Diana Macpherson (NIWA), who provided access to samples and associated sample data. I also want to acknowledge the following research programs that funded the collection studied. Voyage TAN 1802 : the Ross Sea Marine Environment & Ecosystem Voyage 2018 in the Ross Sea sector of Antarctica and the Southern Ocean on the R/V Tangaroa was carried out by NIWA in collaboration with the University of Auckland, jointly funded by the Ministry of Business, Innovation and Employment, NIWA, the Deep South National Science Challenge, the New Zealand Antarctic Research Institute (NZARI), and the University of Auckland. Stations beginning with TRIP : specimens were collected under the Scientific Observer Program funded by the New Zealand Ministry for Primary Industries. Dr. Ben Sharp, New Zealand Scientific Committee representative to the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) Convention, for approving the provision of the sample data, MPI and CCAMLR Observers for collecting the samples at sea. Dr. Steve Parker (NIWA) for coordinating the collection of CCAMLR VME program samples. References El Beshbeeshy M (2011) Thekate Hydroiden von Patagonischen Schelf (Cnidaria, Hydrozoa, Thecata). Verh Naturwiss Ver Hamburg 46:19–233. Hickson SJ, Gravely FH (1907) Coelenterata. 11. Hydroid zoophytes. In: National Antarctic expedition (S.S. Discovery) 1901–1904. Nat Hist 3:1–34 Peña Cantero AL (2006) Benthic hydroids from the south of Livingston Island (South Shetland Islands, Antarctica) collected by the Spanish Antarctic expedition Bentart 94. Deep Sea Res II 53:932–948 Peña Cantero AL (2010) Benthic hydroids (Cnidaria: Hydrozoa) from Peter I Island (Southern Ocean, Antarctica). Polar Biol 33:761–773 Peña Cantero AL (2009) Benthic hydroids (Cnidaria, Hydrozoa) from the Balleny Islands (Antarctica). Polar Biol 32:1743–1751 Peña Cantero AL (2012) Filling biodiversity gaps: benthic hydroids from the Bellingshausen Sea (Antarctica). Polar Biol 35:851–865. https://doi.org/10.1007/s00300-011-1130-y Peña Cantero AL (2014a) Benthic hydroids (Cnidaria, Hydrozoa) from the continental shelf and slope off Queen Mary Coast (East Antarctica). Polar Biol 37:1711–1731. https://doi.org/10.1007/s00300-014-1556-0 Peña Cantero AL (2014b) Benthic hydroids (Cnidaria, Hydrozoa). In: De Broyer C, Koubbi P, Griffiths HJ et al. (eds) Biogeographic Atlas of the Southern Ocean. Scientific Committee on Antarctic Research, Cambridge, pp 103–106 Peña Cantero AL (2017) Benthic hydroids (Cnidaria, Hydrozoa) from the Ross Sea (Antarctica) collected by the New Zealand Antarctic expedition BioRoss 2004 with RV Tangaroa. Zootaxa 4293:1–65. https://doi.org/10.11646/ZOOTAXA.4293.1.1 Peña Cantero AL (2019) Benthic hydroids off Scott Island and the shelf and slope of the Ross Sea (Antarctica) collected during the IPY-CAML TAN0802 voyage by R/V Tangaroa. Mar Biodivers 49:863–885. https://doi.org/10.1007/s12526-018-0865-x Peña Cantero AL (2020) Species of Acryptolaria Norman, 1875 (Cnidaria: Hydrozoa) collected by US Antarctic and subAntarctic expeditions. Zootaxa 4767(2):277–294. https://doi.org/10.11646/zootaxa.4767.2.4 Peña Cantero AL (2021) Additions to knowledge of the biodiversity of benthic hydroids (Cnidaria: Hydrozoa) in the Balleny Islands (Antarctica). Zootaxa 4966(3):321–336. https://doi.org/10.11646/zootaxa.4966.3.4 Peña Cantero AL (2023) New insights into the diversity and ecology of benthic hydroids (Cnidaria, Hydrozoa) from the Ross Sea (Antarctica). Polar Biol 46:933–957. https://doi.org/10.1007/s00300-023-03175-z Peña Cantero AL (2024) New insights into the biodiversity of benthic hydroids (Cnidaria, Hydrozoa) from seamounts in the remote Macquarie Ridge, with the description of three new species. Zool Stud 63:17. https://doi.org/10.6620/ZS.2024.63-17 Peña Cantero AL, Ramil F (2006) Benthic hydroids associated with volcanic structures from Bransfield Strait (Antarctica) collected by the Spanish Antarctic expedition GEBRAP96. Deep Sea Res II 53:949–958. https://doi.org/10.1016/j.dsr2.2006.02.007 Peña Cantero AL, Svoboda A, Vervoort W (2004) Antarctic hydroids (Cnidaria: Hydrozoa) of the families Campanulinidae, Lafoeidae and Campanulariidae from recent Antarctic expeditions with R.V. Polarstern, with the description of a new species. J Nat Hist 38:2269–2303. https://doi.org/10.1080/00222930310001647361 Peña Cantero AL, Boero F, Piraino S (2013) Shallow-water benthic hydroids from Tethys Bay (Terra Nova Bay, Ross Sea, Antarctica). Polar Biol 36:731–753. https://doi.org/10.1007/s00300-013-1299-3 Picken GB (1985) Marine habitats – benthos. In: Bonner WN and Walton DWH (eds) Key Environments: Antarctica. Pergamon Press Ltd, Oxford, pp 154–172 Ralph PM (1957) New Zealand thecate hydroids. Part I. Campanulariidae and Campanulinidae. Trans Proc Royal Soc New Zeal 84:811–854 Schuchert P (2001) Hydroids of Greenland and Iceland (Cnidaria, Hydrozoa). Meddel Grønland, Bioscience 53:1–184 Soto Àngel JJ, Peña Cantero AL (2015) On the benthic hydroids from the Scotia Arc (Southern Ocean): new insights into their biodiversity, ecology and biogeography. Polar Biol 38:983–1007. https://doi.org/10.1007/s00300-015-1660-9 Soto Àngel JJ, Peña Cantero AL (2019) Benthic hydroids (Cnidaria, Hydrozoa) from the Weddell Sea (Antarctica). Zootaxa 4570(1):1–78. https://doi.org/10.11646/zootaxa.4570.1.1 Stepanjants SD (1979) Hydroids of the Antarctic and Subantarctic waters. Biol Res Soviet Antarct Exped 6 20:1–200 (in Russian) Totton AK (1930) Coelenterata. Part V. Hydroida. Nat Hist Rep Br Antarct Terra Nova Exped 1910 5:131–252 (pls 1–3) Vervoort W (1972) Hydroids from the Theta, Vema and Yelcho cruises of the Lamont-Doherty geological observatory. Zool Verh 120:1–247 Watson JE (2003) Deep-water hydroids (Hydrozoa: Leptolida) from Macquarie Island. Mem Mus Vic 60:151–180 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 26 Sep, 2024 Read the published version in Polar Biology → Version 1 posted Editorial decision: Revision requested 15 Aug, 2024 Reviews received at journal 14 Aug, 2024 Reviews received at journal 12 Aug, 2024 Reviewers agreed at journal 24 Jul, 2024 Reviewers agreed at journal 22 Jul, 2024 Reviewers invited by journal 18 Jul, 2024 Editor assigned by journal 18 Jul, 2024 Submission checks completed at journal 04 Jul, 2024 First submitted to journal 03 Jul, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4679741","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":331363757,"identity":"aaf97cee-b6f5-479e-9db5-434dbbeac557","order_by":0,"name":"Álvaro Luis Peña Cantero","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA0klEQVRIiWNgGAWjYDACdgglA6EqiNHCDKF4INQZkrUwthGhg7+Zx/BzRQVQi3TzsQc/5x1ObGBvf4BXi8RhHmPJM2eAWmSOpRv2bgNq4TljgN+aw2wJko1tQC0SOWYSvNsOGwMZ+HXIH2ZL/gnRkv9N8u8coBb55/gdZnCY+RjMFjZp3obDcgwSDPgdZgjUYtlwRoKHTeaYmTTQP3JsPDn4tcgdb2y+2VBhI8cv3fxM8k2NNQ8/+3H8DoMCCQY2CSiTjRj1MF2jYBSMglEwCrADABuhODWHoWxWAAAAAElFTkSuQmCC","orcid":"","institution":"University of Valencia","correspondingAuthor":true,"prefix":"","firstName":"Álvaro","middleName":"Luis Peña","lastName":"Cantero","suffix":""}],"badges":[],"createdAt":"2024-07-03 10:37:11","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4679741/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4679741/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s00300-024-03300-6","type":"published","date":"2024-09-26T15:56:57+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":61347798,"identity":"175f9c98-f6f3-4d6e-abe0-ac665a797a11","added_by":"auto","created_at":"2024-07-29 18:18:42","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":932318,"visible":true,"origin":"","legend":"\u003cp\u003eArea of study and location of the sampling stations (see Table 1 for more details)\u003c/p\u003e","description":"","filename":"Fig1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4679741/v1/549efef98022d2d10c03cdcb.jpg"},{"id":61345927,"identity":"a96921a9-59ef-4c1e-a85d-7bf7d0c3b273","added_by":"auto","created_at":"2024-07-29 18:02:41","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":3757561,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eTurritopsis\u003c/em\u003e sp.: a, stem fragment showing double-layered perisarc; b, distal part of stem; c, polyp showing tentacles at different levels; d, polyp; e, detail of tentacle; f, microbasic euryteles; g, \u003cem\u003eidem\u003c/em\u003e discharged; h, desmonemes. Scale bars: a−d = 200 μm; e = 100 μm; f−h = 10 μm\u003c/p\u003e","description":"","filename":"Fig2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4679741/v1/b4cfb2f25601e0a707eb312c.jpg"},{"id":61345930,"identity":"6a328cc0-5a8b-47c9-b077-38b1aa6d9e97","added_by":"auto","created_at":"2024-07-29 18:02:42","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":4428454,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eAcryptolaria frigida\u003c/em\u003e Peña Cantero, 2014: a, hydrotheca. \u003cem\u003eFilellum liberum\u003c/em\u003e Peña Cantero, 2024: b−c, hydrothecae; d, gonothecae. \u003cem\u003eLafoea dumosa\u003c/em\u003e(Fleming, 1820): e, hydrotheca. \u003cem\u003eLafoea\u003c/em\u003esp.: f, hydrotheca; g, microbasic mastigophores (arrow pointing at shaft of broken nematocyst). \u003cem\u003eTulpa diverticulata\u003c/em\u003eTotton, 1930: h, hydrotheca and diverticulum (arrow). Scale bars: h (inner figure) = 500 μm; a−f, h = 200 μm; g = 10 μm\u003c/p\u003e","description":"","filename":"Fig3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4679741/v1/0feb89d287b85c389f424f3a.jpg"},{"id":61345933,"identity":"85ff475c-e8ec-4e5a-8e8e-c8284715a29f","added_by":"auto","created_at":"2024-07-29 18:02:42","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":4010196,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eSymplectoscyphus frondosus\u003c/em\u003e Peña Cantero, 2010: a, hydrothecae. \u003cem\u003eSymplectoscyphus nesioticus\u003c/em\u003e Blanco, 1977: b, hydrotheca. \u003cem\u003eSertularella pseudovervoorti\u003c/em\u003e Peña Cantero, 2019: c−d, hydrothecae and branch origin; e−f, hydrothecae. \u003cem\u003eHydrodendron arboreum\u003c/em\u003e (Allman, 1888): g, internode with hydrotheca and nematotheca (arrow pointing to location of extra nematophore), h, nematotheca. Scale bars: a−g = 200 μm; h = 100 μm\u003c/p\u003e","description":"","filename":"Fig4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4679741/v1/204fae959ed9f49cd6a542f5.jpg"},{"id":61345928,"identity":"9a78a215-c5f7-4cff-ae3c-2b74b5cc1ed7","added_by":"auto","created_at":"2024-07-29 18:02:42","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":551069,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eHalecium divergens\u003c/em\u003e sp. nov.: a, basal part of a stem showing first hydrothecate internode without apophysis and first regular internode originating from within distal hydrotheca; b, basal part of a stem with a ‘typical’ internode with distal hydrotheca and apophysis; c, stem internode; d, female gonotheca; e, male gonotheca. Scale bar: 250 μm\u003c/p\u003e","description":"","filename":"Fig5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4679741/v1/272ff51b92e99fe0a7b52b36.jpg"},{"id":61346718,"identity":"938b9a37-3947-408a-b2a8-bd2bec641a47","added_by":"auto","created_at":"2024-07-29 18:10:42","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":4540219,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eHalecium divergens\u003c/em\u003e sp. nov.: a, stem fragment showing internode arrangement; b, regular internode originating from within hydrotheca of first stem internode; c, typical stem internode; d, hydrotheca; e, female gonotheca (lateral view); f, detail of female gonothecal aperture; g, male gonotheca; h, microbasic eurytele. Scale bars: a−c, e, g = 200 μm; d, f = 100 μm; h = 10 μm\u003c/p\u003e","description":"","filename":"Fig6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4679741/v1/f958cf0035e97750bf4af0c8.jpg"},{"id":61345929,"identity":"61cb4016-33e3-40bc-b5e4-bb893c3e422a","added_by":"auto","created_at":"2024-07-29 18:02:42","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":3052199,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eHalecium jaederholmi\u003c/em\u003e Vervoort, 1972: a, internode showing hydrotheca and branch origin with one intermediate internode; b, \u003cem\u003eidem\u003c/em\u003e with several intermediate internodes; c, hydrotheca; d, detail of adcauline hydrothecal wall (arrow); e, female gonotheca; f, microbasic eurytele. Scale bars: a−c, e = 200 μm; d = 100 μm; f = 10 μm\u003c/p\u003e","description":"","filename":"Fig7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4679741/v1/822095f1fe1459f68376f0c8.jpg"},{"id":61345935,"identity":"5889ea84-1b1b-48d1-8621-784b263bb6be","added_by":"auto","created_at":"2024-07-29 18:02:42","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":445793,"visible":true,"origin":"","legend":"\u003cp\u003eKnown geographic distribution of \u003cem\u003eS. frondosus\u003c/em\u003e (yellow circles representing previous records; red one present record)\u003c/p\u003e","description":"","filename":"Fig8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4679741/v1/2718931d78baff288b0425e8.jpg"},{"id":65627236,"identity":"38777b33-9696-424d-a323-51d99d87f094","added_by":"auto","created_at":"2024-09-30 16:13:39","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":22402719,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4679741/v1/ec2bc2f1-6b54-47ca-82e0-f6f24c032a0e.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Deep-sea benthic hydroids (Cnidaria, Hydrozoa) from Antarctic submarine ridges off the Ross Sea (Antarctica)","fulltext":[{"header":"Introduction","content":"\u003cp\u003eWhile we have acquired considerable knowledge of the Antarctic benthic hydroid fauna inhabiting the continental shelf waters, particularly in relatively well-studied areas, such as the Weddell Sea (Soto \u0026Agrave;ngel and Pe\u0026ntilde;a Cantero \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) and the Ross Sea (Pe\u0026ntilde;a Cantero \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), little is known about the hydrozoan fauna dwelling on the continental slope or in deeper waters, except for a few exceptions (e.g. Pe\u0026ntilde;a Cantero \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Additionally, despite the Southern Ocean extending significantly norhwards, studies have usually been conducted in waters close to the continent or the few islands surrounding it, such as the Balleny Islands (Pe\u0026ntilde;a Cantero \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), Peter I Island (Pe\u0026ntilde;a Cantero \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2010\u003c/span\u003e) or Scott Island (Pe\u0026ntilde;a Cantero \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). In fact, apart from Pe\u0026ntilde;a Cantero\u0026rsquo;s (\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) study, which focused on hydroids from the Ross Sea, but also from the remote Scott Island area, no hydroids have been studied from bottoms away from the Antarctic continent or its surrounding islands.\u003c/p\u003e \u003cp\u003eI present here the results of a study on a small collection of benthic hydroids from deep waters off the Ross Sea, collected during several New Zealand research surveys. Much of the value of this study lies in its focus on deep-water habitats of the Southern Ocean located far from the Antarctic continent, which, as mentioned before, are practically unexplored for benthic hydroids. On the other hand, while the boundaries of the Southern Ocean are well defined for the pelagos by the Polar Front, they are less clear for the benthos (Picken \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e1985\u003c/span\u003e). Studies like this will contribute to defining those boundaries.\u003c/p\u003e"},{"header":"Material and methods","content":"\u003cp\u003eThe material studied was collected during the New Zealand TAN1802 scientific survey, conducted on board the R/V \u003cem\u003eTangaroa\u003c/em\u003e, and operations of fishing vessels under the New Zealand Scientific Observer Programme (TRIP2993 and TRIP2996). The samples studied here were gathered using an epibenthic sledge and bottom longlines from a series of submarine ridges north of the Ross Sea (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), at depths between 652 and 1770 m (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Hydrozoans were preserved in 70% ethanol.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eStation data\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStation\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDate\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eLatitude (S)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eLongitude (W)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eDepth (m)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eGear\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTAN1802/186\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e08/03/2018\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e66.7448\u0026thinsp;\u0026minus;\u0026thinsp;66.7467\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e177.093\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e652\u0026thinsp;\u0026minus;\u0026thinsp;654\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eEpibenthic sled\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTRIP2993/11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e07/12/2009\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e64.5541\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e171.2308\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1533\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eBottom longline\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTRIP2993/20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e11/12/2009\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e64.5716\u0026thinsp;\u0026minus;\u0026thinsp;64.59\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e171.1216\u0026thinsp;\u0026minus;\u0026thinsp;171.2216\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1770\u0026thinsp;\u0026minus;\u0026thinsp;1541\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eBottom longline\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTRIP2996/1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e05/12/2009\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e65.5441\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e175.7558\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1637\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eBottom longline\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe material studied here is deposited in the National Institute of Water and Atmospheric Research Invertebrate Collection at Wellington (NIWA), New Zealand.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003e\u003cstrong\u003eSpecies account\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eOceaniidae Eschscholtz, 1829\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eTurritopsis\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;sp.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e(Fig. 2)\u003c/p\u003e\n\u003cp\u003eMaterial examined. \u003cstrong\u003eTAN 1802/186\u003c/strong\u003e, a few stems up to 5 mm high, on a bryozoan.\u003c/p\u003e\n\u003cp\u003eDescription.\u0026nbsp;Hydrorhiza stolonal, creeping on bryozoan, giving rise to unbranched, erect stems\u0026nbsp;up to 5 mm high, each with a single distal polyp. Stem\u0026nbsp;covered with firm double-layered perisarc (Fig. 2a);\u0026nbsp;outer\u0026nbsp;layer not reaching pedicel end (Fig. 2b). Hydranth 350–400\u0026nbsp;µm high, 200\u0026nbsp;µm in maximum diameter, with about 12 filiform tentacles at different levels (Fig. 2c-e).\u003c/p\u003e\n\u003cp\u003eCnidome (Fig. 2f-h) consisting of microbasic euryteles (8.6±0.4 x 5.0±0.2\u0026nbsp;µm, range 8-9 x 4.5-5\u0026nbsp;µm) and desmonemes (5.5 x 3.5\u0026nbsp;µm).\u003c/p\u003e\n\u003cp\u003eRemarks. The material is infertile, and only a few poorly preserved polyps are present, preventing a complete characterization and identification of the species.\u003c/p\u003e\n\u003cp\u003eThe only material from Antarctic waters so far assigned to the genus \u003cem\u003eTurritopsis\u003c/em\u003e is that described by Peña Cantero et al. (2013), which is also based on infertile material. The material studied here differs by having unbranched stems, but this could be related to the smaller size of the stems (up to 5 mm high here and up to 15 mm in the material studied by Peña Cantero et al. 2013). These authors indicated that Stepanjants’ (1979) material of \u003cem\u003eCorydendrium\u003c/em\u003e could actually belong to \u003cem\u003eTurritopsis\u003c/em\u003e.\u003c/p\u003e\n\u003cp\u003eEcology and distribution. The material studied by Peña Cantero et al. (2013) was collected at a depth of 20 m from Tethys Bay, in the Ross Sea. Present material comes from much deeper waters (652–654 m).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFamily Lafoeidae Hincks, 1868\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eAcryptolaria frigida\u003c/em\u003e Peña Cantero, 2014\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e(Fig. 3a)\u003c/p\u003e\n\u003cp\u003eMaterial examined.\u0026nbsp;\u003cstrong\u003eTAN1802/186\u003c/strong\u003e, three stems 150, 150 and 130 mm high, one of them with coppinia, basibiont of \u003cem\u003eLafoea dumosa\u003c/em\u003e.\u003c/p\u003e\n\u003cp\u003eDescription. Polysiphonic stem up to 150 mm high. Branching alternate, almost in one plane, usually every third hydrotheca; branches up to third order observed.\u0026nbsp;Hydrothecae alternately arranged approximately in one plane.\u003c/p\u003e\n\u003cp\u003eHydrotheca markedly curved abcaudally (Fig. 3a), tubular, cylindrical at free part, smoothly tapering basally at adnate portion. Hydrotheca adnate to internode for about two- thirds of its length. Adcauline wall strongly convex. Abcauline wall concave, especially at distal half. Hydrothecal aperture circular, directed outwards. Rim even, sometimes with a few short renovations.\u003c/p\u003e\n\u003cp\u003eCoppinia without defensive tubes; gonothecae distally broken.\u003c/p\u003e\n\u003cp\u003eMeasurements (in µm). \u003cem\u003eHydrothecae\u003c/em\u003e: abcauline wall 1450–1650, free part of adcauline wall 380–810, adnate part of adcauline wall 1200–1350, adcauline wall 1730–2010, diameter at aperture 280.\u0026nbsp;\u003cem\u003eCnidome\u003c/em\u003e: larger microbasic mastigophores 20.0±0.6 x 6.8±0.4 (n=10), range 19.0–20.5 x 6.5–7.5\u0026nbsp;µm.\u003c/p\u003e\n\u003cp\u003eRemarks. The material studied perfectly matches previous descriptions of the species in both the shape and size of the hydrotheca and the cnidome.\u003c/p\u003e\n\u003cp\u003eEcology and distribution. \u003cem\u003eAcryptolaria frigida\u003c/em\u003e is known from depths between 85 (Peña Cantero 2010) and 728 m (Peña Cantero 2014); present material at a depth of 652−654 m. Coppiniae in March.\u003c/p\u003e\n\u003cp\u003eCircum-Antarctic distribution (Peña Cantero 2014). It has been reported from the Weddell Sea (Peña Cantero et al. 2004; Soto Àngel and Peña Cantero 2019; Peña Cantero 2020), off Peter I Island (Peña Cantero 2010) and from the Bellingshausen Sea (Peña Cantero 2012), in West Antarctica, and off Queen Mary Coast (Peña Cantero 2014), in East Antarctica. Present material represents the first record for this sector of the Antarctic region.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eFilellum\u003c/em\u003e \u003cem\u003eliberum\u003c/em\u003e Peña Cantero, 2024\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e(Fig. 3b-d)\u003c/p\u003e\n\u003cp\u003eMaterial examined. \u003cstrong\u003eTRIP2993/20\u003c/strong\u003e, several hydrothecae, on axis of dead gorgonian, with coppinia.\u003c/p\u003e\n\u003cp\u003eDescription. Stolonal colony consisting of stolons creeping on a gorgonian axis, giving rise to erect, tubiform, completely free hydrothecae (Fig. 3b-c) of highly variable shape and size (up to 770 µm high). Hydrothecal diameter clearly increasing distally from origin; hydrothecal aperture circular (120–150 µm in diameter), rim even, slightly flared, frequently with several renovations of variable length (Fig. 3b-c).\u003c/p\u003e\n\u003cp\u003eCoppinia consisting of tightly packed gonothecae surrounded by a fence of protective tubes arching over them, creating a protective brooding chamber. Defensive tubes unforked, distally open, and basally partially coalescent. Gonothecae flask-shaped, with a circular aperture on a short distal neck, distally flared (Fig. 3d).\u003c/p\u003e\n\u003cp\u003eRemarks. The present material perfectly agrees with the orginal description of both the hydrothecae and the coppinia. The species is characterised by having completely free hydrothecae.\u003c/p\u003e\n\u003cp\u003eEcology and distribution. \u003cem\u003eFilellum liberum\u003c/em\u003e seems to be a deep-water species. It was known from depths between 505 and 1064 m (Waston 2003 as \u003cem\u003eLafoea tenellula\u003c/em\u003e Allman, 1877, see Peña Cantero 2024); present material collected at depths between 1541 and 1770 m, distinctly increasing its lower bathymetric limit. Coppiniae are known in January (Watson 2003), April (Peña Cantero 2024) and December (present study).\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eFilellum liberum\u003c/em\u003e is known only from waters around Macquarie Island (Peña Cantero 2024) and the Long Ridge area (present study).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eLafoea dumosa\u0026nbsp;\u003c/em\u003e(Fleming, 1820)\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e(Fig. 3e)\u003c/p\u003e\n\u003cp\u003eMaterial examined. \u003cstrong\u003eTAN1802/186\u003c/strong\u003e, a few stems up to 15 mm high, on \u003cem\u003eA. frigida\u003c/em\u003e.\u003c/p\u003e\n\u003cp\u003eDescription.\u0026nbsp;Monosiphonic stems up to 12 mm high, unbranched, with up to 15 hydrothecae alternately arranged in two planes, forming an acute angle. Two polysiphonic stems also present, 16 and 10 mm high, with five and two primary branches, respectively. Branches originating from accessory tubes. Hydrothecae straight (Fig. 3e), mostly cylindrical, tapering at their basal third into a twisted pedicel. Hydrothecal aperture circular; rim even.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eMeasurements (in µm). \u003cem\u003eHydrotheca\u003c/em\u003e: height from ring of desmocytes 550–630, pedicel 200–250, diameter at aperture 160–200. \u003cem\u003eTotal length (hydrotheca plus pedicel)\u003c/em\u003e: 750–880. \u003cem\u003eCnidome\u003c/em\u003e: isorhizas 20.4±0.8 x 10.6±0.7 (n=5), range 19.0–21.0 x 10.0–11.5.\u003c/p\u003e\n\u003cp\u003eEcology and distribution.\u0026nbsp;In Antarctic waters, \u003cem\u003eLafoea dumosa\u003c/em\u003e is known from depths between 12 (Stepanjants 1979) and 1157 m (Peña Cantero 2014); present material at a depth of 652–654 m.\u003c/p\u003e\n\u003cp\u003eCosmopolitan distribution (Stepanjants 1979). In the region, reported from the Ross Sea (Totton 1930; Peña Cantero 2017, 2023) and the Balleny Islands (Peña Cantero 2021).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eLafoea\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;sp.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e(Fig. 3f-g)\u003c/p\u003e\n\u003cp\u003eMaterial examined. \u003cstrong\u003eTRIP2993/20\u003c/strong\u003e, several stems up to 13 mm high, on axis of a dead gorgonian and \u003cem\u003eHalecium divergens\u003c/em\u003e sp. nov.\u003c/p\u003e\n\u003cp\u003eDescription.\u0026nbsp;Stems up to 13 mm high, either monosiphonic or polysiphonic. Branching present only on polysiphonic stems; branches originating from accessory tubes. Hydrothecae alternately arranged in two planes, forming an acute angle. Hydrothecae typically curved abcaudally (Fig. 3f), relatively long and thin, cylindrical for most of their length, tapering only at their basal fourth into a twisted pedicel. Hydrothecal aperture circular; rim even, usually with numerous renovations (up to ten observed).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eMeasurements (in µm). \u003cem\u003eHydrotheca\u003c/em\u003e: height 450–500, diameter at aperture 80–120. \u003cem\u003eTotal length (hydrotheca plus pedicel)\u003c/em\u003e: 600. \u003cem\u003eCnidome\u003c/em\u003e: microbasic mastigophores 6–6.5 x 2.5–3.\u003c/p\u003e\n\u003cp\u003eRemarks. There are also stolonal hydrothecae, on both \u003cem\u003eHalecium divergens\u003c/em\u003e sp. nov. and the gorgonian axis.\u003c/p\u003e\n\u003cp\u003eThe present material is clearly different from \u003cem\u003eL. dumosa\u003c/em\u003e, both in the shape and size of the hydrotheca (e.g. 160–200\u0026nbsp;µm in diameter at the aperture in the material of \u003cem\u003eL. dumosa\u003c/em\u003e studied here), as well as in the cnidome. After several attempts\u0026nbsp;to study the cnidome of this species, I have been unable to find the large isorhizas characterising \u003cem\u003eL. dumosa\u003c/em\u003e (Schuchert 2001). Only small microbasic mastigophores were found (Fig. 3g). Although I could not observe them discharged, I did find a broken nematocyst exposing a short, isometric shaft (Fig. 3g). The scarcity of the available material and the absence of coppinia prevent me from fully characterising this species.\u003c/p\u003e\n\u003cp\u003eEcology and distribution. \u003cem\u003eLafoea\u003c/em\u003e sp. was collected at depths between 1541 and 1770 m, epibiotic on the axis of a gorgonian and on \u003cem\u003eH. divergens\u003c/em\u003e sp. nov.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFamily Campanulariidae Johnston, 1836\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eTulpa\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;\u003cem\u003ediverticulata\u003c/em\u003e Totton, 1930\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e(Fig. 3h)\u003c/p\u003e\n\u003cp\u003eMaterial examined. \u003cstrong\u003eTAN 1802/186\u003c/strong\u003e, several stems up to 60 mm, on axis of dead gorgonian, basibiont of \u003cem\u003eSymplectoscyphus\u003c/em\u003e\u003cem\u003enesioticus\u003c/em\u003e.\u003c/p\u003e\n\u003cp\u003eDescription. Stems up to 60 mm high, monosiphonic, with alternate hydrothecae in an almost unilateral arrangement. Hydrothecae on pedicels of variable length, frequently with regenerations. Hydrotheca tubular (Fig. 3h), with diameter increasing from diaphragm to basal third, then slightly decreasing to distal third, and finally widening again to aperture. Rim of hydrothecal aperture even, but everted and sinuous. Hydrothecal wall with more or less marked facets, fading basally. A few short renovations of hydrothecal rim might be present. Hydrotheca with distal diverticulae (Fig. 3h).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eMeasurements (in µm). \u003cem\u003eStolon\u003c/em\u003e: diameter 380. \u003cem\u003ePedicel\u003c/em\u003e: length 1800–4000. \u003cem\u003eHydrotheca\u003c/em\u003e: height 2900–3400, diameter at aperture 1000–1300.\u003c/p\u003e\n\u003cp\u003eRemarks. There are a few records of the species, but most of them are dubious because the peculiar diverticulae characterising this species (Totton 1930) were neither described nor depicted; only Ralph (1957) noted their presence in her material.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eEcology and distribution.\u0026nbsp;\u003cem\u003eTulpa diverticulata\u003c/em\u003e is known for sure from a depth of 456 m (Totton 1930); present material collected at a depth of 652−654 m.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;The species is certainly present in New Zealand waters (Totton 1930; Ralph 1957).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSymplectoscyphidae Maronna, Miranda, Peña Cantero, Barbeitos and Marques, 2016\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eSymplectoscyphus frondosus\u0026nbsp;\u003c/em\u003ePeña Cantero, 2010\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e(Fig. 4a)\u003c/p\u003e\n\u003cp\u003eMaterial examined.\u0026nbsp;\u003cstrong\u003eTRIP 2996/1\u003c/strong\u003e, one stem 100 mm high, broken into three main fragments, on coral.\u003c/p\u003e\n\u003cp\u003eDescription. Stem erect, 100 mm high, rigid, markedly tortuous, strongly polysiphonic (diameter at basal part 3 mm). Branches more or less perpendicular to long axis of stem, strongly polysiphonic over great extent, tightly packed, and approximately of similar development, giving stem a bottlebrush appearance. Primary branches spirally arranged, completing a turn every five branches.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eBranches and stems divided into short internodes by alternating oblique nodes, each internode with one hydrotheca. Hydrothecae alternately arranged in approximately one plane, densely packed, with distal part of each hydrotheca clearly overlapping basal part of following one (Fig. 4a). Hydrotheca slightly curved abcaudally. Adcauline wall adnate to internode for about half its length; free part of adcauline wall slightly convex or straight. Abcauline wall slightly convex basally and slightly concave distally. Rim of hydrothecal aperture with three cusps separated by deep embayments. Hydrothecal diameter distinctly decreasing towards aperture.\u003c/p\u003e\n\u003cp\u003eMeasurements (in µm). \u003cem\u003eHydrotheca\u003c/em\u003e: abcauline wall 360–400, free part of adcauline wall 210–260, adnate part of adcauline wall 210–270, adcauline wall 420–500, diameter at aperture 110–130, maximum diameter 150, diameter at base 110.\u003c/p\u003e\n\u003cp\u003eEcology and distribution. Shelf and slope species, known from depths between 321 and 2283 m (Peña Cantero 2019); present material collected at a depth of 1637 m.\u003c/p\u003e\n\u003cp\u003ePreviously considered endemic to the eastern Ross Sea (Peña Cantero 2017, 2019), the present material, outside the typical area, represents its northernmost recorded occurence.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eSymplectoscyphus nesioticus\u003c/em\u003e Blanco, 1977\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e(Fig. 4b)\u003c/p\u003e\n\u003cp\u003eMaterial examined. \u003cstrong\u003eTAN 1802/186\u003c/strong\u003e, a few stems up to 10 mm high, on \u003cem\u003eT. diverticulata\u003c/em\u003e and axis of a dead gorgonian.\u003c/p\u003e\n\u003cp\u003eDescription. Monosiphonic, unbranched stems up to 10 mm high and nine hydrothecae. Stem internodes in marked zigzag, each with a distal hydrotheca.\u003c/p\u003e\n\u003cp\u003eHydrotheca tubular, free for most of its adcauline wall (Fig. 4b); free part of adcauline wall slightly convex. Hydrotheca usually with distinct inflexion point where adcauline wall becomes free. Abcauline wall slightly concave. Hydrothecal aperture with three sharp cusps separated by deep embayments. Hydrothecal diameter usually increasing distally.\u003c/p\u003e\n\u003cp\u003eMeasurements (in µm). \u003cem\u003eHydrotheca\u003c/em\u003e: abcauline wall 370–430, free part of adcauline wall 230–400, adnate part of adcauline wall 80–100, adcauline wall 310, diameter at aperture 180–200.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eEcology and distribution. Shelf species (Peña Cantero 2017), collected at depths from 56 (Peña Cantero 2006) to 701 m (Peña Cantero 2014);\u0026nbsp;present material found at a depth of 652–654 m.\u003c/p\u003e\n\u003cp\u003eCircum-Antarctic distribution (Peña Cantero 2014). In the region, known from the Ross Sea (Peña Cantero 2017) and from a seamount of the nearby Scott Island (Peña Cantero 2019).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eHaleciidae Hincks, 1868\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eHalecium divergens\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;sp. nov.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e(Figs 5–6)\u003c/p\u003e\n\u003cp\u003eMaterial examined.\u0026nbsp;\u003cstrong\u003eTRIP 2993/20\u003c/strong\u003e, several stems up to 10 mm high, with gonothecae, on axis of dead gorgonian (Holotype, NIWA 131355).\u003c/p\u003e\n\u003cp\u003eDescription.Monosiphonic stems, up to 10 mm high, arising from stolons creeping on axis of dead gorgonian. Stems resting on stolonal apophyses (Fig. 5a–b), sometimes followed by an athecate internode (Fig. 5b). First hydrothecate internode either ‘typical’ (Fig. 5b) with distal hydrotheca and apophysis supporting successive internode, or without apophysis and first regular internode originating within distal hydrotheca (Figs 5a, 6b). Successive typical internodes in marked zigzag (Fig. 6a) (angle about 70°) and resting on strong apophysis originating from below hydrotheca (Fig. 5a–b). New branches originating from hydrophores of lower-order hydrothecae. Distance between hydrotheca and apophyses small (Fig. 6b-d), resulting in a free and very short hydrophore. Internodes usually very long, with a basal swelling.\u003c/p\u003e\n\u003cp\u003eHydrothecae alternately arranged in one plane (Fig. 6a), placed at end of a short, free hydrophore (Figs 5a–c, 6b–c); ratio between adcauline length of hydrophore and diameter at diaphragm 0.2–0.5. Without pseudodiaphragm, but sometimes with thin perisarc projection on adcauline side of hydrophore (Fig. 5b). Hydrothecae usually at level of basal node of following internode (Figs 5a–b, 6b–d), relatively high, strongly widening distally (Figs 5a–c, 6b–d), with everted rim (Fig. 6d) and ring of desmocytes above diaphragm. Up to third-order hydrothecae observed on long and smooth hydrophores.\u003c/p\u003e\n\u003cp\u003eGonothecae extremely flat and concave (spoon-shaped), with distal aperture, resting on a short pedicel originating directly from stolon (Fig. 6e). Putative male gonotheca roughly rounded (Figs 5e, 6g). Putative female gonotheca larger (Figs 5d, 6e), with distinctly longer pedicel, two basal lobes, and aperture forming a sort of embayment (Figs 5d, 6f).\u003c/p\u003e\n\u003cp\u003eMeasurements (in µm).\u003cem\u003eStolonal apophyses\u003c/em\u003e: length 100-150 (350), width 110–140. \u003cem\u003eInternodes\u003c/em\u003e: length 1400–1800 (up to hydrothecal diaphragm), wide 120–150. \u003cem\u003eHydrothecae\u003c/em\u003e: height 60–90, diameter at aperture 210–270, diameter at diaphragm 150–170. \u003cem\u003eAdcauline length of hydrophore\u003c/em\u003e: 30–50. \u003cem\u003eLower-order hydrophore\u003c/em\u003e: length up to 950. \u003cem\u003eFemale gonothecae\u003c/em\u003e: height 1450, width 1100, aperture 200. \u003cem\u003eMale gonotheca\u003c/em\u003e: height 1000, width 870, aperture 190. \u003cem\u003eCnidome\u003c/em\u003e: microbasic euryteles 10–11 x 4.5–5.5 and microbasic mastigophores 7.5 x 2.\u003c/p\u003e\n\u003cp\u003eRemarks.The extreme flatness of the gonothecae is likely due to the fact that they have already shed their contents. On one occasion, a gonotheca was found originating from below the hydrotheca of the first stem internode; the rest of the many gonothecae present in the studied material arise directly from the stolons.\u003c/p\u003e\n\u003cp\u003eAs mentioned earlier, there are two types of stems based on the structure of the first internode. Some stems begin with a regular internode that includes a distal hydrotheca and an apophysis below it supporting the following internode (Fig. 5b). In contrast, other stems start with an internode that has a distal hydrotheca but lacks an apophysis. In this case, the next internode originates from the hydrophore of a lower-order hydrotheca, typically a secondary hydrotheca (Fig. 5a), although it may also originate from an even lower-order hydrotheca.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe species has free hydrophores, a feature shared with a group of other Antarctic species of \u003cem\u003eHalecium\u003c/em\u003e (\u003cem\u003eH. antarcticum\u003c/em\u003e Vanhöffen, 1910, \u003cem\u003eH. banzare\u003c/em\u003e Watson, 2008, \u003cem\u003eH. exaggeratum\u003c/em\u003e Peña Cantero, Boero and Piraino, 2013, \u003cem\u003eH. frigidum\u003c/em\u003e Peña Cantero, 2010, \u003cem\u003eH. interpolatum\u003c/em\u003e Ritchie, 1907, \u003cem\u003eH. pallens\u003c/em\u003e Jäderholm, 1904 and \u003cem\u003eH. pseudodelicatulum\u003c/em\u003e Peña Cantero, 2014). However, it differs from all these species because the hydrophore is distinctly much shorter. The closest species in this feature is \u003cem\u003eH. interpolatum\u003c/em\u003e, although that length is still significantly longer in Ritchie’s species; the ratio between the adcauline length of the hydrophore and the diameter at the diaphragm is around 0.8–0.9 in \u003cem\u003eH. interporlatum\u003c/em\u003e, but only 0.2–0.5 in the present species.\u003c/p\u003e\n\u003cp\u003eBy the size and general shape of the hydrotheca it is also closest to \u003cem\u003eH. interpolatum\u003c/em\u003e. However, they differ in colony and internode structure. In Ritchie’s species, the stems, basally polysiphonic and slightly geniculate, give rise to paired branches originating from the hydrophore of a primary hydrotheca. \u003cem\u003eHalecium interpolatum\u003c/em\u003e is also distinctive in the shape of the internodes, which have a long and straight basal part followed by one or two annulations. Neither of those features are found in the present species. Finally, while the gonothecae develop from within the hydrotheca in \u003cem\u003eH. interpolatum\u003c/em\u003e, in the present species, as mentioned earlier, they arise from the stolons.\u003c/p\u003e\n\u003cp\u003eEcology and distribution. \u003cem\u003eHalecium divergens\u003c/em\u003e sp. nov. was collected at depths between 1541 and 1770 m, on the axis of a dead gorgonian. Gonothecae in December.\u003c/p\u003e\n\u003cp\u003eEtymology. The specific name \u003cem\u003edivergens\u003c/em\u003e makes reference to the marked different directions taken by the successive internodes. From New Latin \u003cem\u003edivergens.\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eHalecium jaederholmi\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;Vervoort, 1972\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e(Fig. 7)\u003c/p\u003e\n\u003cp\u003eMaterial examined. \u003cstrong\u003eTRIP 2993/11\u003c/strong\u003e, a few stems up to 60 mm high, with one female gonotheca, on axis of a dead gorgonian.\u003c/p\u003e\n\u003cp\u003eDescription. Stems up to 60 mm high, honey-coloured, polysiphonic and branched.\u0026nbsp;Branching irregular, sometimes branches almost unilateral and nearly perpendicular to plane of hydrothecae. Branches resting on large apophysis originating from hydrophore of a hydrotheca, usually on one lateral, although closer to abcauline side. Typically, one ahydrothecate internode after apophysis (Fig. 7a), sometimes more (Fig. 7b). Occasionally, branches originating from inside a hydrotheca.\u003c/p\u003e\n\u003cp\u003eStem and branches divided into internodes by slightly oblique alternating nodes; one hydrotheca per internode. Hydrothecae arranged alternately in two planes, forming an angle of about 70°.\u0026nbsp;Primary hydrothecae resting on sessile hydrophores (Fig. 7a–c). Adcauline hydrothecal wall much more developed than abcauline one and completely adnate to internode (Fig. 7a, c–d), frequently extending to distal node (Fig. 7d). Hydrothecal aperture slightly directed downwards (Fig. 7b). One secondary hydrotheca sometimes present, not resting on a hydrophore and, therefore, practically within primary hydrotheca. Secondary hydrotheca approximately equally developed all around.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFemale gonotheca kidney-shaped (Fig. 7e), with two hydrothecae at the concave side.\u003c/p\u003e\n\u003cp\u003eMeasurements (in m). \u003cem\u003eInternode\u003c/em\u003e: length 750–1000, wide 150–180. \u003cem\u003eHydrothecae\u003c/em\u003e: height 30–40, diameter at aperture\u0026nbsp;180–190, diameter at diaphragm 160–180. \u003cem\u003eHydrophore\u003c/em\u003e: adcauline length 120–150. \u003cem\u003eGonotheca\u003c/em\u003e: height 1500, maximum diameter 600. \u003cem\u003eCnidome\u003c/em\u003e: microbasic euryteles 11.0±0.7 x 5.1±0.2 (n= 10), range 10–12 x 5.0–5.5, microbasic mastigophore 7.5 x 3.\u003c/p\u003e\n\u003cp\u003eRemarks.\u0026nbsp;There is usually an ahydrothecate internode after the apophyses supporting the branches, although there may be even more (up to eight have been observed). However, this seems to be related to fractures. In fact, ahydrothecate internodes may also be found along the branches, clearly indicating that they formed following a fracture.\u003c/p\u003e\n\u003cp\u003eEcology and distribution.Shelf and slope species, collected at depths from 24 (Vervoort 1972) to 950 m (Peña Cantero 2019);\u0026nbsp;present material found at a depth of 1533 m, extending significantly its lower bathymetric limit.Gonotheca in December.\u003c/p\u003e\n\u003cp\u003ePan-Antarctic distribution (Peña Cantero 2014). In the region, reported from the Ross Sea (Peña Cantero 2017) and from seamounts of the nearby Scott Island (Peña Cantero 2019).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFamily Sertularellidae Maronna, Miranda, Peña Cantero, Barbeitos and Marques, 2016\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eSertularella\u003c/em\u003e \u003cem\u003epseudovervoorti\u003c/em\u003e Peña Cantero, 2019\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e(Fig. 4c–f)\u003c/p\u003e\n\u003cp\u003eMaterial examined.\u0026nbsp;\u003cstrong\u003eTRIP 2993/20\u003c/strong\u003e, a few stems up to 10 mm high, on axis of a dead gorgonian.\u003c/p\u003e\n\u003cp\u003eDescription. Monosiphonic stems up to 10 mm high and five hydrothecae, unbranched or scarcely branched (up to second-order branches present). Branches originating below a hydrotheca (Fig. 4c–e). Stem divided into relatively long and thin internodes by slightly marked, alternating, oblique nodes. Internodes arranged in a marked zigzag pattern. First stem internode much longer.\u003c/p\u003e\n\u003cp\u003eHydrotheca cylindrical, practically straight, free for most of its adcauline length (Fig. 4c–f). Maximum diameter distinctly above adnate part; diameter slightly decreasing distally and more markedly basally. Abcauline wall either approximately straight or slightly convex basally and concave distally. Free part of adcauline wall slightly convex, with three or four slight undulations; adnate part practically straight. With distinct inflexion point between free and adnate parts of adcauline wall. Rim of hydrothecal aperture with four small, equally developed cusps, separated by shallow embayments.\u003c/p\u003e\n\u003cp\u003eMeasurements (in μm): \u003cem\u003eInternodes\u003c/em\u003e: length 1220–4400 (first internode 2600–4400), diameter at hydrothecal base 170–200. \u003cem\u003eHydrothecae\u003c/em\u003e: length of abcauline wall 500–550, free part of adcauline wall 320–450, adnate part of adcauline wall 150–250, adcauline wall 550–640, diameter at aperture 190–250, maximum diameter 230–290.\u003c/p\u003e\n\u003cp\u003eRemarks. The stems are either unbranched or scarcely branched. Only four stems are branched, usually having one or two primary branches; only one stem has a second-order branch. This particular stem, approximately 8 mm high, has a primary branch originating below its fourth hydrotheca. This primary branch, in turn, gives rise to an incipient secondary branch at its third hydrotheca, which has not yet formed a hydrotheca.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe position of the primary branch is variable; it has been observed at the first, second, fourth, or fifth hydrotheca in different stems.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe main axis of the stems has up to five hydrothecae, although some of the branched stems have up to eight hydrothecae in total.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe first internode is distinctly longer than the remaining stem internodes, their length decreasing distally; for instance, in one stem, the length of the first four internodes was 4400, 2100, 1420 and 1220 µm, respectively.\u003c/p\u003e\n\u003cp\u003eThe colony structure and the shape of the hydrotheca in the studied material perfectly agree with the type material of \u003cem\u003eS. pseudovervoorti\u003c/em\u003e, although the hydrothecae are distinctly smaller. However, this difference could be attributed to intraspecific variation. It is important to note that knowledge of this species is based on very limited material. \u003cem\u003eSertularella pseudovervoorti\u003c/em\u003e was previously known only from the original description, which was based on a few stems up to 15 mm high. Consequently, I am considering the present material as belonging to \u003cem\u003eS. pseudovervoorti\u003c/em\u003e, which, in addition, was discovered in the nearby Scott Island area.\u003c/p\u003e\n\u003cp\u003eEcology and distribution. \u003cem\u003eSertularella pseudovervoorti\u003c/em\u003e was previously known from depths between 1520 and 1560 m (Peña Cantero 2019); present material collected between 1541 and 1770 m, slightly increasing its lower bathymetric limit. It has been found growing on the axis of dead gorgonians (Peña Cantero 2019; present material).\u003c/p\u003e\n\u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;This represents the second record of the species. It was previously known only from a seamount off Scott Island (Peña Cantero 2019).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePhylactothecidae Stechow, 1921\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eHydrodendron arboreum\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;(Allman, 1888)\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e(Fig. 4g–h)\u003c/p\u003e\n\u003cp\u003eMaterial examined. \u003cstrong\u003eTAN 1802/186\u003c/strong\u003e, three stems up to 50 mm, on axis of gorgonian.\u003c/p\u003e\n\u003cp\u003eDescription. Stems polysiphonic, up to 50 mm high, branched. Branching in one plane, in subopposite pairs. Only primary branches present, monosiphonic. Stem and branches divided into relatively long internodes bearing one hydrotheca each.\u003c/p\u003e\n\u003cp\u003eHydrothecae alternately arranged in one plane. Hydrotheca on a short hydrophore provided with a distinct free part (Fig. 4g). Hydrothecae completely free (Fig. 4g), low, with a ring of desmocytes between diaphragm and aperture; abcauline and adcauline wall straight, the former slightly abcaudally directed. Hydrothecal diameter barely increasing distally. Hydrothecal aperture circular, markedly tilted abcaudally; rim even. Lower-order hydrothecae (up to fourth-order observed) usually present (Fig. 4g), on short hydrophores, with a ring of desmocytes, and a circular aperture (rim slightly everted); hydrothecal diameter distinctly increasing distally. Typically, one nematophore per internode, on opposite side of hydrotheca, but an extra nematophore also common\u0026nbsp;on abcauline side of primary hydrophore (Fig. 4g). Nematophores provided with small cone-shaped nematotheca with desmocytes (Fig. 4h).\u003c/p\u003e\n\u003cp\u003eMeasurements (in m). \u003cem\u003eInternode\u003c/em\u003e: length 840–1500, diameter at distal node 180–210. \u003cem\u003eHydrothecae\u003c/em\u003e: height 20–30, diameter at aperture\u0026nbsp;210–240, diameter at diaphragm 200–230. \u003cem\u003eHydrophore\u003c/em\u003e: adnate part 230–240, free part 20–70. \u003cem\u003eNematotheca\u003c/em\u003e: height 60–80, diameter at aperture 75–80.\u003c/p\u003e\n\u003cp\u003eRemarks. All the stems are polysiphonic, although they are provided with a significant monosiphonic distal part. The stems are also branched, except for the smallest. The branches are typically monosiphonic, although one branch has a small basal portion with incipient polysiphony.\u003c/p\u003e\n\u003cp\u003eBranching appears to occur in subopposite pairs, which is evident in the most developed stem. This stem has six primary branches arranged in three subopposite pairs.\u003c/p\u003e\n\u003cp\u003eEcology and distribution. Eurybathic species found at depths from 18 (Hickson and Gravely 1907) to 1370 m (Peña Cantero and Ramil 2006); present material\u0026nbsp;collected\u0026nbsp;at a depth of\u0026nbsp;652−654\u0026nbsp;m.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; Pan-Antarctic distribution (Peña Cantero and Ramil 2006). In the region, frequently reported from the Ross Sea (cf. Peña Cantero 2017) and once from the Balleny Islands (Peña Cantero 2009).\u003c/p\u003e"},{"header":"Discussion","content":"\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eBiodiversity\u003c/h2\u003e \u003cp\u003eAs shown above, 12 species were found in the studied collection, gathered from an Antarctic area where knowledge of benthic hydroids was non-existent. Among the material examined, only one species of Anthoathecata was present, belonging to the family Oceaniidae. The remaining hydroids belong to Leptothecata, with Lafoeidae being the most diverse family, represented by four species. Haleciidae and Symplectoscyphidae each have two species, while the families Campanulariidae, Phylactothecidae and Sertularellidae are each represented by one species.\u003c/p\u003e \u003cp\u003eThe occurrence of species in this study is extremely low as all of them were present at only one station. The station with the highest species diversity was TAN1802/186 with six species, followed by TRIP2993/20 with four. Only one species was found at each of the other two stations (TRIP2996/1 and TRIP2993/11). This variation could be related to the sampling gear employed; at the station with the highest species diversity, samples were collected using an epibenthic sledge, whereas the other samples were obtained using bottom longlines. The relatively high species diversity in sample TRIP2993/20, compared to the other samples obtained with bottom longlines, is clearly related to the fact that the species were growing on the axis of a gorgonian. Depth could also play a role in the species richness observed. The bottoms sampled in TAN1802/186 are distincly shallower (652\u0026ndash;654 m) than those from the remaining samples: TRIP2993/11 (1533 m), TRIP2993/20 (1541\u0026ndash;1770 m) and TRIP2996/1 (1637 m). TAN1802/186 is also the closest station to the Antarctic continent.\u003c/p\u003e \u003cp\u003eA comparision of the benthic hydroid species diversity found in the studied collection with that present in the neighbouring areas (the Ross Sea, the Balleny Islands and the Scott Island area) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) shows that it is much lower than in the Ross Sea, where a total of 84 species have been reported, making it the third region with the highest number of benthic hydroids among the larger Antarctic areas (Pe\u0026ntilde;a Cantero \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). The much higher diversity in the Ross Sea can partially be explained by the high number of samples containing hydroids (more than a hundred) studied from that region, as well as by the wide bathymetric range surveyed, extending from the tidal level to depths of the continental slope (up to 1865 m). The species richness is also significant lower than that of the Balleny Islands, where a total of 34 species are known (Pe\u0026ntilde;a Cantero \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). As with the Ross Sea, a larger number of samples (about thirty) have been studied from the Balleny Islands, and the bathymetric range surveyed (63 to 702 m) covers shallower bottoms. Regarding the Scott Island area, the species diversity is however similar [11 species are known (Pe\u0026ntilde;a Cantero \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2019\u003c/span\u003e)], despite the fact that the number of samples studied, coming from a similar bathymetric range (300 to 1560 m), is significantly higher (15 samples compared to four here).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eBiogeography\u003c/h2\u003e \u003cp\u003eFrom a biogeographical perspective, it is worth mentioning the case of \u003cem\u003eS. frondosus\u003c/em\u003e. This species is relatively abundant in the shelf and slope of the eastern Ross Sea (Pe\u0026ntilde;a Cantero \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2017\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Its absence from the nearby areas of the Balleny Islands (Pe\u0026ntilde;a Cantero \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2009\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) and Scott Island (Pe\u0026ntilde;a Cantero \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2019\u003c/span\u003e), previously prompted me to consider it to be endemic to the eastern Ross Sea (Pe\u0026ntilde;a Cantero \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). However, the present study has demonstrated that its known distribution extends much further north (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn the opposite direction we find the case of \u003cem\u003eT. diverticulata\u003c/em\u003e and the genus \u003cem\u003eTulpa\u003c/em\u003e, never before reported in the Southern Ocean. \u003cem\u003eTulpa diverticulata\u003c/em\u003e was originally described from New Zealand (Totton \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e1930\u003c/span\u003e), and there have been a few unconfirmed or doubtful records in sub-Antarctic waters, but none in Antarctic waters. As for the genus, the closest record to Antarctic waters is for \u003cem\u003eTulpa tulipifera\u003c/em\u003e (Allman, 1888) from the sub-Antarctic Burdwood Bank (El Beshbeeshy \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Soto \u0026Agrave;ngel and Pe\u0026ntilde;a Cantero, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). The discovery of \u003cem\u003eT. diverticulata\u003c/em\u003e in the present study, at almost 67\u0026deg;S, confirms the presence of this species, and the genus \u003cem\u003eTulpa\u003c/em\u003e, well within waters of the Southern Ocean.\u003c/p\u003e \u003cp\u003eIt is also worth mentioning the discovery of the newly described \u003cem\u003eF. liberum\u003c/em\u003e, previously known only from the vicinity of Macquarie Island (Pe\u0026ntilde;a Cantero \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Together with \u003cem\u003eT. diverticulata\u003c/em\u003e, this species is a clear example of the biogeographic links between the Southern Ocean and the sub-Antarctic Macquarie Ridge and New Zealand.\u003c/p\u003e \u003cp\u003eConcerning the faunistic relationships of the study area with neighbouring regions (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), among the eleven species known from the remote Scott Island area (Pe\u0026ntilde;a Cantero \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2019\u003c/span\u003e), three are present in the studied collection (\u003cem\u003eH. jaederholmi\u003c/em\u003e, \u003cem\u003eS. pseudovervoorti\u003c/em\u003e and \u003cem\u003eS. nesioticus\u003c/em\u003e). \u003cem\u003eHalecium jaederhomi\u003c/em\u003e and \u003cem\u003eS. nesioticus\u003c/em\u003e are also found in Antarctic continental shelf waters, but \u003cem\u003eS. pseudovervoorti\u003c/em\u003e is known only from the Scott Island area and the area studied here, suggesting it may be endemic to this part of the Southern Ocean. Relationships with the Balleny Islands are weaker, with only two out of the 34 species known from that area (Pe\u0026ntilde;a Cantero \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) present in the studied collection: \u003cem\u003eL. dumosa\u003c/em\u003e, which has a worldwide distribution, and \u003cem\u003eH. arboreum\u003c/em\u003e, widely reported in Antarctic and sub-Antarctic waters. Finally, of the 84 species known from the Ross Sea, only five are present in the studied collection: \u003cem\u003eL. dumosa\u003c/em\u003e (cosmopolitan distribution), \u003cem\u003eH. jaederholmi\u003c/em\u003e and \u003cem\u003eH. arboreum\u003c/em\u003e (Pan-Antarctic distribution), \u003cem\u003eS. nesioticus\u003c/em\u003e (circum-Antarctic distribution), and \u003cem\u003eS. frondosus\u003c/em\u003e, previously considered endemic to the eastern Ross Sea.\u003c/p\u003e \u003cp\u003eIn general, while acknowledging the limitations in drawing general conclusions due to our limited knowledge of hydroid diversity in the studied area, the fauna inhabiting these waters cannot be considered a typical Antarctic fauna. Several reasons support this assertion. First, the presence of endemic species (\u003cem\u003eH. divergens\u003c/em\u003e sp. nov., known only from the study area, and \u003cem\u003eS. pseudovervoorti\u003c/em\u003e, found exclusively here and in the nearby Scott Island area). Second, the presence of species unknown from the Antarctic region (i.e., \u003cem\u003eF. liberum\u003c/em\u003e and \u003cem\u003eT. diverticulata\u003c/em\u003e). Finally, the complete absence of representatives from the most characteristic genera of Antarctic benthic hydroids: \u003cem\u003eAntarctoscyphus\u003c/em\u003e, \u003cem\u003eOswaldella\u003c/em\u003e, \u003cem\u003eSchizotricha\u003c/em\u003e and \u003cem\u003eStaurotheca\u003c/em\u003e. These four genera, along with \u003cem\u003eHalecium\u003c/em\u003e and \u003cem\u003eSymplectoscyphus\u003c/em\u003e, account for about 75% of the Leptothecata species diversity in the Antarctic (Pe\u0026ntilde;a Cantero 2014b). The last two genera, which are represented in the studied collection by two species each, have a much broader distribution and are extensively represented outside the Antarctic region.\u003c/p\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eCompeting interests\u0026nbsp;\u003c/strong\u003eThe author declares no competing interests\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of interest\u0026nbsp;\u003c/strong\u003eThe author declares that there is no conflict of interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contribution\u0026nbsp;\u003c/strong\u003eThe author carried out all aspects of the present study.\u003c/p\u003e\u003cp\u003e\u003cstrong\u003eAcknowledgements\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eI want to express my gratitude to the NIWA Invertebrate Collection, Sadie Mills, Di Tracey, and Diana Macpherson (NIWA), who provided access to samples and associated sample data. I also want to acknowledge the following research programs that funded the collection studied. \u003cem\u003eVoyage TAN 1802\u003c/em\u003e:\u0026nbsp;the \u003cem\u003eRoss Sea Marine Environment \u0026amp; Ecosystem Voyage 2018\u003c/em\u003e in the Ross Sea sector of Antarctica and the Southern Ocean on the R/V \u003cem\u003eTangaroa\u003c/em\u003e was carried out by NIWA in collaboration with the University of Auckland, jointly funded by the Ministry of Business, Innovation and Employment, NIWA, the Deep South National Science Challenge, the New Zealand Antarctic Research Institute (NZARI), and the University of Auckland.\u0026nbsp;\u003cem\u003eStations beginning with TRIP\u003c/em\u003e: specimens were collected under the Scientific Observer Program funded by the New Zealand Ministry for Primary Industries. Dr. Ben Sharp, New Zealand Scientific Committee representative to the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) Convention, for approving the provision of the sample data, MPI and CCAMLR Observers for collecting the samples at sea. Dr. Steve Parker (NIWA) for coordinating the collection of CCAMLR VME program samples.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eEl Beshbeeshy M (2011) Thekate Hydroiden von Patagonischen Schelf (Cnidaria, Hydrozoa, Thecata). Verh Naturwiss Ver Hamburg 46:19\u0026ndash;233.\u003c/li\u003e\n\u003cli\u003eHickson SJ, Gravely FH (1907) Coelenterata. 11. Hydroid zoophytes. In: National Antarctic expedition (S.S. Discovery) 1901\u0026ndash;1904. Nat Hist 3:1\u0026ndash;34\u003c/li\u003e\n\u003cli\u003ePe\u0026ntilde;a Cantero AL (2006) Benthic hydroids from the south of Livingston Island (South Shetland Islands, Antarctica) collected by the Spanish Antarctic expedition Bentart 94. Deep Sea Res II 53:932\u0026ndash;948\u003c/li\u003e\n\u003cli\u003ePe\u0026ntilde;a Cantero AL (2010) Benthic hydroids (Cnidaria: Hydrozoa) from Peter I Island (Southern Ocean, Antarctica). Polar Biol 33:761\u0026ndash;773\u003c/li\u003e\n\u003cli\u003ePe\u0026ntilde;a Cantero AL (2009) Benthic hydroids (Cnidaria, Hydrozoa) from the Balleny Islands (Antarctica). Polar Biol 32:1743\u0026ndash;1751\u003c/li\u003e\n\u003cli\u003ePe\u0026ntilde;a Cantero AL (2012) Filling biodiversity gaps: benthic hydroids from the Bellingshausen Sea (Antarctica). Polar Biol 35:851\u0026ndash;865. https://doi.org/10.1007/s00300-011-1130-y\u003c/li\u003e\n\u003cli\u003ePe\u0026ntilde;a Cantero AL (2014a) Benthic hydroids (Cnidaria, Hydrozoa) from the continental shelf and slope off Queen Mary Coast (East Antarctica). Polar Biol 37:1711\u0026ndash;1731. https://doi.org/10.1007/s00300-014-1556-0\u003c/li\u003e\n\u003cli\u003ePe\u0026ntilde;a Cantero AL (2014b) Benthic hydroids (Cnidaria, Hydrozoa). In: De Broyer C, Koubbi P, Griffiths HJ et al. (eds) Biogeographic Atlas of the Southern Ocean. Scientific Committee on Antarctic Research, Cambridge, pp 103\u0026ndash;106\u003c/li\u003e\n\u003cli\u003ePe\u0026ntilde;a Cantero AL (2017) Benthic hydroids (Cnidaria, Hydrozoa) from the Ross Sea (Antarctica) collected by the New Zealand Antarctic expedition BioRoss 2004 with RV Tangaroa. Zootaxa 4293:1\u0026ndash;65. https://doi.org/10.11646/ZOOTAXA.4293.1.1\u003c/li\u003e\n\u003cli\u003ePe\u0026ntilde;a Cantero AL (2019) Benthic hydroids off Scott Island and the shelf and slope of the Ross Sea (Antarctica) collected during the IPY-CAML TAN0802 voyage by R/V Tangaroa. Mar Biodivers 49:863\u0026ndash;885. https://doi.org/10.1007/s12526-018-0865-x\u003c/li\u003e\n\u003cli\u003ePe\u0026ntilde;a Cantero AL (2020) Species of \u003cem\u003eAcryptolaria\u003c/em\u003e Norman, 1875 (Cnidaria: Hydrozoa) collected by US Antarctic and subAntarctic expeditions. Zootaxa 4767(2):277\u0026ndash;294. https://doi.org/10.11646/zootaxa.4767.2.4\u003c/li\u003e\n\u003cli\u003ePe\u0026ntilde;a Cantero AL (2021) Additions to knowledge of the biodiversity of benthic hydroids (Cnidaria: Hydrozoa) in the Balleny Islands (Antarctica). Zootaxa 4966(3):321\u0026ndash;336. https://doi.org/10.11646/zootaxa.4966.3.4\u003c/li\u003e\n\u003cli\u003ePe\u0026ntilde;a Cantero AL (2023) New insights into the diversity and ecology of benthic hydroids (Cnidaria, Hydrozoa) from the Ross Sea (Antarctica). Polar Biol 46:933\u0026ndash;957. https://doi.org/10.1007/s00300-023-03175-z\u003c/li\u003e\n\u003cli\u003ePe\u0026ntilde;a Cantero AL (2024) New insights into the biodiversity of benthic hydroids (Cnidaria, Hydrozoa) from seamounts in the remote Macquarie Ridge, with the description of three new species. Zool Stud 63:17. https://doi.org/10.6620/ZS.2024.63-17\u003c/li\u003e\n\u003cli\u003ePe\u0026ntilde;a Cantero AL, Ramil F (2006) Benthic hydroids associated with volcanic structures from Bransfield Strait (Antarctica) collected by the Spanish Antarctic expedition GEBRAP96. Deep Sea Res II 53:949\u0026ndash;958. https://doi.org/10.1016/j.dsr2.2006.02.007\u003c/li\u003e\n\u003cli\u003ePe\u0026ntilde;a Cantero AL, Svoboda A, Vervoort W (2004) Antarctic hydroids (Cnidaria: Hydrozoa) of the families Campanulinidae, Lafoeidae and Campanulariidae from recent Antarctic expeditions with R.V. Polarstern, with the description of a new species. J Nat Hist 38:2269\u0026ndash;2303. https://doi.org/10.1080/00222930310001647361\u003c/li\u003e\n\u003cli\u003ePe\u0026ntilde;a Cantero AL, Boero F, Piraino S (2013) Shallow-water benthic hydroids from Tethys Bay (Terra Nova Bay, Ross Sea, Antarctica). Polar Biol 36:731\u0026ndash;753. https://doi.org/10.1007/s00300-013-1299-3\u003c/li\u003e\n\u003cli\u003ePicken GB (1985) Marine habitats \u0026ndash; benthos. In: Bonner WN and Walton DWH (eds) Key Environments: Antarctica. Pergamon Press Ltd, Oxford, pp 154\u0026ndash;172\u003c/li\u003e\n\u003cli\u003eRalph PM (1957) New Zealand thecate hydroids. Part I. Campanulariidae and Campanulinidae. Trans Proc Royal Soc New Zeal 84:811\u0026ndash;854 \u003c/li\u003e\n\u003cli\u003eSchuchert P (2001) Hydroids of Greenland and Iceland (Cnidaria, Hydrozoa). Meddel Gr\u0026oslash;nland, Bioscience 53:1\u0026ndash;184\u003c/li\u003e\n\u003cli\u003eSoto \u0026Agrave;ngel JJ, Pe\u0026ntilde;a Cantero AL (2015) On the benthic hydroids from the Scotia Arc (Southern Ocean): new insights into their biodiversity, ecology and biogeography. Polar Biol 38:983\u0026ndash;1007. https://doi.org/10.1007/s00300-015-1660-9\u003c/li\u003e\n\u003cli\u003eSoto \u0026Agrave;ngel JJ, Pe\u0026ntilde;a Cantero AL (2019) Benthic hydroids (Cnidaria, Hydrozoa) from the Weddell Sea (Antarctica). Zootaxa 4570(1):1\u0026ndash;78. https://doi.org/10.11646/zootaxa.4570.1.1\u003c/li\u003e\n\u003cli\u003eStepanjants SD (1979) Hydroids of the Antarctic and Subantarctic waters. Biol Res Soviet Antarct Exped 6 20:1\u0026ndash;200 (in Russian)\u003c/li\u003e\n\u003cli\u003eTotton AK (1930) Coelenterata. Part V. Hydroida. Nat Hist Rep Br Antarct Terra Nova Exped 1910 5:131\u0026ndash;252 (pls 1\u0026ndash;3)\u003c/li\u003e\n\u003cli\u003eVervoort W (1972) Hydroids from the Theta, Vema and Yelcho cruises of the Lamont-Doherty geological observatory. Zool Verh 120:1\u0026ndash;247\u003c/li\u003e\n\u003cli\u003eWatson JE (2003) Deep-water hydroids (Hydrozoa: Leptolida) from Macquarie Island. Mem Mus Vic 60:151\u0026ndash;180\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"polar-biology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"pobi","sideBox":"Learn more about [Polar Biology](http://link.springer.com/journal/300)","snPcode":"300","submissionUrl":"https://submission.nature.com/new-submission/300/3","title":"Polar Biology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Hydrozoans, Biodiversity, New species, New records, Biogeography","lastPublishedDoi":"10.21203/rs.3.rs-4679741/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4679741/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eKnowledge of benthic hydroids inhabiting the Antarctic continental shelf waters, particularly of relatively well-studied areas, has increased in recent years. This has allowed us to recognise them as one of the main and most characteristic zoological groups of the Antarctic benthos. However, little is known about the hydroids dwelling on the continental slope or deeper waters, let alone on bottoms away from the Antarctic continent, despite the fact that the Southern Ocean extends significantly norhwards. This study contributes to reducing that knowledge gap by studying material collected from a series of deep-sea ridges north of the Ross Sea, from which hydrozoans have never been reported. Twelve species, including \u003cem\u003eHalecium divergens\u003c/em\u003e sp. nov., have been found and studied. Except for \u003cem\u003eTurritopsis\u003c/em\u003e sp., belonging to the Anthoathecata family Oceaniidae, all species belong to Leptothecata, in particular to the families Campanulariidae, Haleciidae, Lafoeidae, Phylactothecidae, Sertularellidae and Symplectoscyphidae. Lafoeidae is the most represented family with four species. \u003cem\u003eSertularella pseudovervoorti\u003c/em\u003e and \u003cem\u003eFilellum liberum\u003c/em\u003e are found for the second time. The discovery of \u003cem\u003eSymplectoscyphus frondosus\u003c/em\u003e, a species previously considered endemic to the shelf and slope of the eastern Ross Sea, significantly extends its known northern distribution limit. \u003cem\u003eTulpa diverticulata\u003c/em\u003e and the genus \u003cem\u003eTulpa\u003c/em\u003e are reported in Antarctic waters for the first time. The lower limit of the bathymetric range for several species has been extended. Despite being well within Antarctic waters, the studied area hosts a very distinctive fauna, markedly different from the typical Antarctic benthic hydroid fauna. Its endemisms, the presence of species unknown in the Antarctic region and the absence of representatives of the most characteristic Antarctic genera account for its originality.\u003c/p\u003e","manuscriptTitle":"Deep-sea benthic hydroids (Cnidaria, Hydrozoa) from Antarctic submarine ridges off the Ross Sea (Antarctica)","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-07-29 18:02:37","doi":"10.21203/rs.3.rs-4679741/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-08-15T17:33:33+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-08-14T23:57:09+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-08-12T14:24:46+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"112926951103524535776663926581567991803","date":"2024-07-24T17:25:56+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"196843830212094028608823154196173901142","date":"2024-07-22T12:50:46+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-07-18T10:26:57+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-07-18T10:07:11+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-07-05T02:28:00+00:00","index":"","fulltext":""},{"type":"submitted","content":"Polar Biology","date":"2024-07-03T10:35:49+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"polar-biology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"pobi","sideBox":"Learn more about [Polar Biology](http://link.springer.com/journal/300)","snPcode":"300","submissionUrl":"https://submission.nature.com/new-submission/300/3","title":"Polar Biology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"629497ca-c469-4c5f-b3b2-57a82f026645","owner":[],"postedDate":"July 29th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2024-09-30T16:02:47+00:00","versionOfRecord":{"articleIdentity":"rs-4679741","link":"https://doi.org/10.1007/s00300-024-03300-6","journal":{"identity":"polar-biology","isVorOnly":false,"title":"Polar Biology"},"publishedOn":"2024-09-26 15:56:57","publishedOnDateReadable":"September 26th, 2024"},"versionCreatedAt":"2024-07-29 18:02:37","video":"","vorDoi":"10.1007/s00300-024-03300-6","vorDoiUrl":"https://doi.org/10.1007/s00300-024-03300-6","workflowStages":[]},"version":"v1","identity":"rs-4679741","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4679741","identity":"rs-4679741","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}