A Paradox: Paucispiral Protoconch in a Widespread Carrier Snail Xenophora conchyliophora

A Paradox: Paucispiral Protoconch in a Widespread Carrier Snail Xenophora conchyliophora | Authorea try { document.documentElement.classList.add('js'); } catch (e) { } var _gaq = _gaq || []; _gaq.push(['_setAccount', 'G-8VDV14Y67G']); _gaq.push(['_trackPageview']); (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); Skip to main content Preprints Collections Wiley Open Research IET Open Research Ecological Society of Japan All Collections About About Authorea FAQs Contact Us Quick Search anywhere Search for preprint articles, keywords, etc. Search Search ADVANCED SEARCH SCROLL This is a preprint and has not been peer reviewed. Data may be preliminary. 2 April 2026 V1 Latest version Share on A Paradox: Paucispiral Protoconch in a Widespread Carrier Snail Xenophora conchyliophora Author : Yu Kai Tan 0000-0002-7216-2258 [email protected] Authors Info & Affiliations https://doi.org/10.22541/au.177514604.48545112/v1 170 views 119 downloads Contents Abstract Information & Authors Metrics & Citations View Options References Figures Tables Media Share Abstract Larval mode is long held as a key determinant of dispersal capacity, geographic range and geologic persistence in benthic marine invertebrates. In gastropods, multispiral protoconchs are associated with prolonged planktotrophic dispersal and broad distributions, whereas paucispiral protoconchs indicate lecithotrophic or direct development and are typically linked to restricted ranges. Here, I report a striking exception in the carrier snail Xenophora conchyliophora, a species distributed across tropical Western Atlantic. Direct examination of rare, well-preserved material reveals a consistently paucispiral protoconch of approximately 1¾–2 whorls. Molecular analysis supports X. conchyliophora as a cohesive species across its range. Despite its inferred low dispersal potential, X. conchyliophora occupies a wide range essentially identical to other planktotrophic xenophores, with a range spanning ~8300 km. This paradox highlights a decoupling between protoconch morphology and realized distribution and suggests that factors such as habitat selection may play a stronger role in shaping species ranges than larval mode alone. The Phase Loop Criterion C. R. Gimarelli (January 10, 2026) \affiliation Independent Researcher A Paradox: Paucispiral Protoconch in a Widespread Carrier Snail Xenophora conchyliophora Yu Kai Tan 1105 N University Avenue, Biological Sciences Building Rm 2070, Ann Arbor, MI 48109, USA. Correspondence: Yu Kai Tan; email: [email protected] Data availability statement All image data in this study are included within the manuscript. Point data for species occurrence are open data publicly accessible through the Global Biodiversity Information Facility (GBIF), whereas specimen data for material examined, in addition to that included herein, are accessible of respective museum online databases. All DNA sequences generated for the molecular phylogenetic analysis will be submitted to GenBank upon acceptance of the manuscript. The Phase Loop Criterion C. R. Gimarelli (January 10, 2026) \affiliation Independent Researcher Abstract Larval mode is long held as a key determinant of dispersal capacity, geographic range and geologic persistence in benthic marine invertebrates. In gastropods, multispiral protoconchs are associated with prolonged planktotrophic dispersal and broad distributions, whereas paucispiral protoconchs indicate lecithotrophic or direct development and are typically linked to restricted ranges. Here, I report a striking exception in the carrier snail Xenophora conchyliophora , a species distributed across tropical Western Atlantic. Direct examination of rare, well-preserved material reveals a consistently paucispiral protoconch of approximately 1¾–2 whorls. Molecular analysis supports X. conchyliophora as a cohesive species across its range. Despite its inferred low dispersal potential, X. conchyliophora occupies a wide range essentially identical to other planktotrophic xenophores, with a range spanning ~8300 km. This paradox highlights a decoupling between protoconch morphology and realized distribution and suggests that factors such as habitat selection may play a stronger role in shaping species ranges than larval mode alone. Keywords marine invertebrates, Mollusca, larval development, biogeography, dispersal ecology Introduction Larval mode is long held as a key determinant of dispersal capacity and geographic ranges of benthic marine invertebrates (Siegel et al., 2003; Scheltema, 1989). Gastropods provide a compelling model system for their study, as the morphology of larval shells, preserved as protoconchs in adult shells, is an indication of their mode of larval development and the duration larvae spent in the plankton, known as pelagic larval duration. Species with multispiral protoconchs typically undergo a prolonged planktotrophic larval stage, during which they have the potential to disperse widely via ocean currents (Jablonski, 1986, Jablonski and Lutz, 1983). Contrarily, species with paucispiral protoconchs undergo a short non-feeding lecithotrophic planktonic larval stage or direct development, hatching as crawl-away juveniles at their parental sites, thus typically have restricted dispersal potential (Jablonski and Lutz, 1983; Shuto, 1974). Empirical studies in some systems support the theoretical prediction that increased dispersibility of planktonic larvae augments their chances of colonizing new locations or replenishing populations at distant sites, thereby maintaining a larger distribution than lecithotrophic or non-planktonic developmental modes (Hansen, 1978; Jablonski, and Lutz, 1983; Jablonski, 1986). Kohn & Perron (1994) found that Indo West Pacific Conus species that are direct developers have significantly smaller range sizes compared to their planktotrophic congeners, as exemplified by direct-developing clades exhibiting microendemicity in southern Australia and Cape Verde. The charismatic carrier snails (Xenophoridae) are unique among molluscs for collecting and affixing foreign objects such as rocks, shells and coral fragments to their shells. Authors have speculated that these shell attachments may provide camouflage or physical defence against predators (e.g., Kreipl & Alf 1999). Many species purportedly exhibit species-specific guilds of collecting behaviour, preferentially collecting certain objects, while others show high levels of variation in agglutinant assemblage across individuals and across populations. The early ontogeny of the carrier snail family Xenophoridae remains largely uncharacterized, despite extensive fascination with their unique behavior of attaching foreign objects onto their shells. There are no reported observations of live xenophore veligers; thus, larval mode is primarily inferred from protoconch morphology. Most xenophore species purportedly possess a multispiral, conical protoconch of three to four whorls measuring approximately 0.8-1.2 mm in diameter (Ponder, 1983). Protoconch multispirality implies planktotrophic veligers capable of extended pelagic dispersal. In agreement with Thorson’s Rule (Thorson, 1950) postulating higher prevalence of planktrophic species in warmer regions, all species with multispiral protoconchs are found across warm tropical and subtropical regions, including Onustus longleyi (Bartsch, 1931), Onustus caribaeus (Petit de la Saussaye, 1857), Xenophora japonica Kuroda & Habe, 1971, Xenophora pallidula (Reeve, 1842). Protoconchs of most other xenophore species, however, have never been directly observed due to poor preservation of protoconchs or obscuration by agglutinants in mature specimens. Among these scant records include the protoconch of an unidentified Xenophora species from the South China Sea, a low-conical multispiral shell of 3½–4 whorls and roughly 1 mm diameter, supporting planktotrophic development common to members of superfamily Stromboidea (Bandel, 1993). A further two post-larval specimens of xenophores bearing multispiral protoconchs were also reported from the Red Sea, identified as Aspidophoreas chinensis (R. A. Philippi, 1842) (Bandel, 2007). Xenophora mediterranea possess 7½ protoconch whorls, and is likely the xenophore with the longest planktonic phase (Gofas et al., 2011) Fossil xenophores such as X. leprosa (S. G. Morton, 1834) † from the Late Cretaceous (Ripley Formation) possess similarly multi-whorled larval shells, demonstrating morphological stability through geologic time. Protoconch multispirality and larval planktotrophy are stipulated as shared traits among xenophores largely based on their prevalence in all observed fossil and extant species, with one exception. Prior to this study, the only living xenophore known to possess a paucispiral protoconch is Austrophora flindersi (Cotton and Godfrey, 1938), which protoconch comprises about 1½ inflated whorls and exceeds 1 mm in diameter (Ponder, 1983), fig. 13 E). This morphology is typical of direct development with crawl-away juveniles or a brief pelagic phase. The species is endemic to Australia, narrowly distributed in the southwestern coast of Australia and Tasmania. This narrow distribution is consistent with the reduced dispersal potential expected of its non-planktonic or lecithotrophic larvae, and contrasts sharply with the broad ranges of its multispiral congeners. Stellaria paucispinosa , endemic to the Gulf of Aden, possesses a protoconch with ca. 2½ whorls, thought to be suggestive of lecithotrophy or a short planktonic phase (Nappo, Bini, and Santucci, 2022). Materials and Methods I examined the protoconch of Xenophora conchyliophora from both in the field and on museum specimens. Intact protoconchs in X. conchyliophora are rarely preserved in mature shells, as the apex is frequently lost to erosion or obscured by agglutinated material. A single juvenile specimen collected by divers via vacuum suction at La Désirade, Guadeloupe (Muséum National d’Histoire Naturelle, Paris: MNHN-IM-2023-493) retains a fully intact protoconch. The specimen was identified as a xenophore, evidenced by seven sand grains agglutinated to its shell — a behaviour unique to Xenophoridae. It was also determined to be post-larval as the agglutinating behaviour onsets only after settlement, in part due to lack of sand grains adrift in the plankton for collection. To verify the protoconch morphology observed with juvenile specimens bearing identifiable diagnostic traits, I examined over 100 specimens of X. conchyliophora from museum collections. Most specimens were too eroded to discern apical morphology. Only two additional specimens retained sufficiently intact or partially preserved protoconchs from which the number of larval whorls could be inferred. These include a subadult specimen from Florida (Florida Museum of Natural History, Gainesville: UF 568180) and a dry adult specimen from the Grand Cayman (Carnegie Museum of Natural History, Pittsburgh: CM 136747). In the latter, the protoconch is largely eroded, but the position of larval whorls can be inferred based on residual shell, changes in shell rugosity, and the position of attachment scars at the protoconch–teleoconch boundary. For comparative purposes, protoconchs of other xenophores are examined, including Western Atlantic species O. caribaeus and O. longleyi , Indo-Pacific species Xenophora pallidula , Australian endemic Austrophora flindersi , and a post-larval specimen of an undetermined xenophore from New Caledonia. Imaging was conducted using a Hitachi TM3030 scanning electron microscope at 15 kV in charge reduction mode. Distributional data for the three Western Atlantic xenophores were compiled from the Global Biodiversity Information Facility (GBIF) and mapped in R implemented in R Studio. To verify that specimens collected across the sampled range belong to the same molecular species, I sequenced X. conchyliophora from distinct parts of the distribution, namely the Florida Keys (United States) and the Lesser Antilles (Guadeloupe and Martinique), and include further specimens of Eastern Pacific sister Xenophora robusta (A. E. Verrill, 1870) , and Western Atlantic specimens O. caribaeus , O. longleyi for assessment of degree of interspecific divergence. Ponderiana digitata (E. von Martens, 1878) was selected as outgroup for tree rooting. Specimens sequenced and corresponding data are provided in Table 1. Total genomic DNA was extracted using the Omega Bio-Tek E.Z.N.A.® Mollusc & Insect DNA Kit according to manufacturer’s protocol. A 658 bp fragment of the cytochrome c oxidase subunit I ( cox1 ) gene was amplified using the universal Folmer primers LCO1490 and HCO2198 (Folmer et al., 1994), with universal synthetic M13 vector primers appended to their 5′ ends (Messing & Vieira, 1982). PCR conditions consisted of an initial denaturation at 94°C for 5 min, followed by 40 cycles of 30 s denaturation at 94°C, 30 s annealing at 48°C, and 30 s extension at 72°C. PCR products were visualized by gel electrophoresis at 90 V and 200 mA for 25 min in a 1.5% agarose gel stained with GelRed in 0.5× TBE buffer. Products showing bands of the expected fragment length were diluted 1:5 and sequenced at Eurofins Scientific. Multiple sequence alignments were performed in MAFFT v7 using the parameter auto-selection strategy (Katoh & Standley, 2013). Gene trees were inferred using a maximum likelihood (ML) approach in IQ-TREE 2 (Minh et al., 2020) under a general time-reversible (GTR) substitution model, with branch support assessed using 1,000 ultrafast bootstrap replicates. Average pairwise genetic distances within and among species were calculated in MEGA12 (Kumar et al. 2024). Kimura two-parameter (K2P) model (Kimura, 1980) with 1000 bootstraps and rate among sites set to gamma-distributed; raw distances (p-distance) were computed with default settings. Results The single post-larval shell from La Désirade, Guadeloupe (MNHN-IM-2023-493) possesses a paucispiral protoconch comprising only 1 ¾ whorls, (Figure 1A-B). The diameter (d) of the protoconch is 1.0 mm. While juvenile xenophore specimens are not easily identified to species by morphology, I was able to assign this specimen confidently to X. conchyliophora as this species is the only one of the three Western Atlantic species that inhabits the depth of the collecting station. Of these three species, X. conchyliophora is the only one for which the protoconch morphology remains undocumented. This species determination is further supported by the collection of live conspecifics at nearby stations (Figure 1C). In mature specimens that can be more confidently identified based on diagnostic traits absent in post-larvae, I was able to identify only two other X. conchyliophora specimens with broken but sufficiently intact protoconchs from which whorl counts could be inferred. The first is a specimen of a subadult specimen from Florida (Florida Museum of Natural History, Gainesville: UF 568180) with morphological traits consistent with X. conchyliophora . This specimen has slightly more developed protoconch with two whorls (d = 1.1 mm, Figure 1D). My attempts to extract DNA from this alcohol preserved specimen for molecular identification were unsuccessful. The second specimen is a dry shell of an adult specimen from Grand Cayman (Carnegie Museum of Natural History, Pittsburgh: CM 136747). The protoconch is almost entirely eroded, but I was able to infer the position of larval whorls based on residual shell along the suture between protoconch and teleoconch (Figure 1E). The position of the nepionic line was determined based on sharp turnover in shell rugosity and position of attachment scars. The inferred protoconch comprises of 1 ¾ whorls (d = 0.9 mm), affirming the paucispirality of X. conchyliophora protoconch seen in the other specimens. Also present on this specimen is a septum that plugs the opening left in the wake of the lost apex (Figure 1E). The other two Western Atlantic species, O. caribaeus and O. longleyi are typically found at depths greater than 150 m, and possess distinct multispiral protoconchs. O. caribaeus (Academy of Natural Sciences at Drexel University, Philadelphia: ANSP 267256, Figure 2A) and O. longleyi (ANSP 193884: Figure 2B) were found to have 2 ½ whorls (d = 1.5 mm) and 3 ½ whorls (d = 1.8 mm) in their protoconchs respectively, with the latter typically showing strong brownish coloration in its larval shell. X. pallidula is multispiral with 3 whorls (University of Michigan Musuem of Zoology, UMMZ MOE: d = 1.7 mm; Figure 2C). I also observed a young post-larva of an undetermined xenophore from New Caledonia with a striking sculptured protoconch comprising 5 whorls (MNHN-IM-2019-35061: d = 1.0 mm; Figure 2 D-E). A. flindersi possesses 1 ¼ protoconch whorls (d = 1.7 mm; Figure 2F). Range maps show that all Western Atlantic species have nearly identical distribution and range size (Figure. 3) Despite scarcity of genetic resources for X. conchyliophora , I was able to attain 16 sequences of this species. Phylogenetic analysis supports the validity of X. conchyliophora , with species forming distinct clades separated by long branches (Figure. 4). X. conchyliophora is clearly delineated from its Western Atlantic congeners, Onustus caribaeus and O. longleyi (Figure. 4). The most northern specimen from Florida Keys (UF 26680) is sister to all individuals from the Lesser Antilles, separated by small pairwise distances (0.015 < K2P < 0.021). The low average genetic distance within the X. conchyliophora (K2P = 0.007, Table 2) further demonstrates the taxonomic integrity of X. conchyliophora across its range. As between species K2P distance are approximately five to ten times higher, ranging between 0.107 and 0.198, the divergence among X. conchyliophora is likelier to reflect population structure. Surprisingly, the analysis recovers Xenophora robusta as sister to the clade containing X. conchyliophora and O. caribaeus , rather than sister to X. conchyliophora itself. The Phase Loop Criterion C. R. Gimarelli (January 10, 2026) \affiliation Independent Researcher Discussion The apparent lack of planktotrophy in X. conchyliophora larvae runs contrary to theoretical expectations. Despite its low dispersal potential, it shares an essentially identical and broad geographic range with other Western Atlantic xenophorids, Onustus caribaeus and O. longleyi , which possess multispiral protoconchs (Figure 3). The linear nautical distance connecting the northern and southern range limits of X. conchyliophora is approximately 8,300 km, far exceeding the general criteria for wide-ranging species defined by Jablonski and colleagues (1983, 1985) Other Xenophoridae species with paucispiral protoconchs, namely A. flindersi and S. paucispinosa exhibit much narrower distributions, consistent with theoretical expectations. Widespread nominal species exhibiting non-planktotrophy, such as the periwinkle Laevilittorina caliginosa (A. A. Gould, 1849), have been found to harbor a complex of cryptic narrow endemics, potentially due to poor dispersibility leading to vicariance and speciation (González‐Wevar, 2022). This does not appear to be the case in X. conchyliophora , here demonstrated to be a cohesive species at the limits of the sampled ranges for specimens examined for protoconchs. Populations in the Dominican Republic are reported to almost exclusively collect smooth siliceous pebbles but show no other distinction in shell morphology (Zimmermann, 2016, VanderVan, 2011). Barring new molecular evidence to the contrary, the divergence in shell attachment assemblage is likely indicative of different local environmental debris available for collection, rather than species level behavioral divergence. Alternatively, post-larval dispersal by rafting on buoyant objects such as bull kelp or driftwood may result in sufficiently frequent transoceanic transport to maintain ranges wider than expected by limited larval dispersal (Donald, Kennedy & Spencer, 2005; Ó Foighil et al., 1999; Johannesson, 1988). Nevertheless, rafting appears unlikely as a mode of secondary adult dispersal in X. conchyliophora , as their soft-bottom habitat precludes them from possessing a large muscular foot requisite for prolonged attachment to hard floating substrates. This discordance between dispersal mode and range size in Western Atlantic xenophores suggest that strong post-settlement biotic filtering or habitat selectivity (Marshall et al., 2010), may exert a stronger influence on colonization than dispersal distance alone. The ”shell-apex theory”, canonized by Powell (1942) and advocated for by Thorson (1950), posits that multispiral larval protoconchs are indicative of long duration of planktic dispersal, allowing species to maintain wider ranges and phylogenetic persistence than non-planktic species. Shuto (1974) made the distinction between the feeding (planktotrophic) and non-feeding (lecithotrophic) modes of planktic larvae, arguing that the former is more dispersive. Jablonski (1985, 1986) and Jablonski and Lutz (1983) made successful predictions of phylogenetic longevity based on dispersal capacity inferred from protoconch morphology. However, Hadfield and Strathmann (1990) argued that this morphological dichotomy fails to account for the fact that planktonic dispersers, irrespective of feeding mode, possess substantially greater dispersal capacities than direct developers. Many trochoidean gastropods, such as Calliostoma ligatum (A. A. Gould, 1849) and Margarites pupillus (A. A. Gould, 1849), violate expectations under the shell-apex paradigm, maintaining long lecithotrophic pelagic durations and geographic distributions comparable to those of planktotrophic species, yet producing protoconchs indistinguishable from those of direct developers (Hadfield and Strathmann, 1990; Desai, 1966; Lebour, 1937). Our molecular data suggest that Xenophora conchyliophora represents a similar decoupling of morphology and life history. Rather than a complex of cryptic, direct-developing endemics, X. conchyliophora is likelier to be one effective lecithotrophic disperser. While this represents a notable exception within the Xenophoridae, it serves as a critical reminder that apical signals can be ”invisible” to traditional analysis, and that broad geographic ranges in paucispiral caenogastropods should not be dismissed as taxonomic artifacts without molecular verification. Acknowledgements I thank the curatorial personnel at MNHN (Nicolas Puillandre, Barbara Buge), UFMNH (John Slapcinsky), ANSP (Paul Callomon), WAM (Corey Whisson, Lisa Kirkendale) and Timothy Pearce (CM) for their support for collection access, Andy D. Y. Tan for assisting with specimen loan and transport, and Rosemary (Rosy) Glos for technical support on the SEM. Many thanks to my advisor, Thomas F. Duda Jr., for providing feedback on the manuscript. Conflict of Interest Statement The author has no conflicts of interest to declare. Funding Statement The sequencing of Guadeloupe specimens is supported by the University of Michigan Museum of Zoology Division of Mollusks John B. Burch Malacology Fund. Instrumentation and equipment used is housed in and supported by the University of Michigan Department of Ecology and Evolutionary Biology. The Phase Loop Criterion C. R. Gimarelli (January 10, 2026) \affiliation Independent Researcher Author Contributions Yu Kai Tan : Conceptualization (lead); Data curation (lead); Formal analysis (lead); Funding acquisition (lead); Investigation (lead); Methodology (lead); Project administration (lead); Resources (lead); Validation (lead); Visualization (lead); Writing – original draft, review and editing (lead). References Bandel, K. (1993). Caenogastropoda during Mesozoic times. Scripta Geologica, Special Issue , 2, 7–56. Bandel, K. (2007). About the larval shell of some Stromboidea, connected to a review of the classification and phylogeny of the Strombimorpha (Caenogastropoda). Freiberger Forschungshefte C , 524, 97–206. Desai, B. N. (1966). The biology of Monodonta lineata (da Costa). 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Romancing the Stones: a shelling expedition to the Dominican Republic. American Conchologist 39 (3), 15-20. Zimmermann, D. (2016). “Got the fever” in the Dominican Republic. American Conchologist 44 (3), 24-31. Table 1. List of molecular specimens. Ponderiana digitata is used as outgroup to root the tree. Lots with more than one sequenced individual are denoted by a full stop (.) followed by a number, with the physical specimens thus labelled. The Phase Loop Criterion C. R. Gimarelli (January 10, 2026) \affiliation Independent Researcher MNHN-IM-2013-60665 Guadeloupe Onustus caribaeus 16°21’N 60°51’W MNHN-IM-2013-60720 Guadeloupe Onustus caribaeus 16°17’N 61°01’W MNHN-IM-2013-60735 Guadeloupe Onustus caribaeus 16°17’N 61°01’W MNHN-IM-2013-60736 Guadeloupe Onustus caribaeus 16°17’N 61°01’W MNHN-IM-2013-60748 Guadeloupe Onustus caribaeus 16°19’N 60°55’W MNHN-IM-2013-60814 Guadeloupe Onustus caribaeus 16°20’N 60°54’W MNHN-IM-2013-60911 Guadeloupe Onustus caribaeus 16°01’N 61°24’W UF 350046 PZ212857 United States Onustus caribaeus 24°37’N 83°39’W UF 350047 PZ212858 United States Onustus caribaeus 24°33’N 83°33’W UF 351147 OR910868.1 United States Onustus caribaeus 27°0’N 84°0’W UF 351181.1 PZ212859 United States Onustus caribaeus 27°44’N 84°36’W UF 351181.3 PZ212860 United States Onustus caribaeus 27°44’”N 84°36’W MNHN-IM-2013-19523 Guadeloupe Xenophora conchyliophora 16°11’N 61°32’W MNHN-IM-2013-19547 Guadeloupe Xenophora conchyliophora 16°11’N 61°32’W MNHN-IM-2013-20788 Guadeloupe Xenophora conchyliophora 16°25’N 61°33’W MNHN-IM-2013-70704 Martinique Xenophora conchyliophora 14°38’N 60°46’W MNHN-IM-2013-70809 Martinique Xenophora conchyliophora 14°42’N 60°50’W MNHN-IM-2013-70810 Martinique Xenophora conchyliophora 14°42’N 60°50’W MNHN-IM-2013-70891 Martinique Xenophora conchyliophora 14°42’N 60°50’W MNHN-IM-2013-71469 Martinique Xenophora conchyliophora 14°39’N 61°09’W MNHN-IM-2013-74250 Martinique Xenophora conchyliophora 14°26’N 60°54’W MNHN-IM-2013-9411 Guadeloupe Xenophora conchyliophora 16°22’N 61°33’W MNHN-IM-2013-9412 Guadeloupe Xenophora conchyliophora 16°22’N 61°34’W MNHN-IM-2013-9413 Guadeloupe Xenophora conchyliophora 16°25’N 61°33’W MNHN-IM-2019-49101 Guadeloupe Xenophora conchyliophora 16°20’N 61°03’W MNHN-IM-2019-50025 Guadeloupe Xenophora conchyliophora 16°20’N 61°03’W MNHN-IM-2019-50515 Guadeloupe Xenophora conchyliophora 16°20’N 61°03’W UF 26680 OR911257.1 United States Xenophora conchyliophora 24°03’N 82°16’W UMMZ 306790 PZ212865 Mauritania Ponderiana digitata 18°26’N 16°07’W UMMZ 306791 PZ212866 Mauritania Ponderiana digitata 18°26’N 16°07’W UMMZ 306792 PZ212867 Mauritania Ponderiana digitata 18°26’N 16°07’W MNHN-IM-2013-56269 French Guiana Onustus longleyi 7°02’N 52°52’W MNHN-IM-2013-56271 French Guiana Onustus longleyi 7°02’N 52°52’W MNHN-IM-2013-56370 French Guiana Onustus longleyi 6°46’N 52°30’W MNHN-IM-2013-56371 French Guiana Onustus longleyi 6°46’N 52°30’W MNHN-IM-2013-60190 Guadeloupe Onustus longleyi 16°29’N 61°42’W MNHN-IM-2013-60192 Guadeloupe Onustus longleyi 16°29’N 61°42’W MNHN-IM-2013-60910 Guadeloupe Onustus longleyi 16°01’N 61°24’W UF 323747 OR910871.1 United States Onustus longleyi 24°28’N 83°29’W UF 350049 PZ212863 United States Onustus longleyi 24°16’N 82°45’W UF 381274.1 PZ212864 United States Onustus longleyi 24°36’N 82°54’W UF 381274.2 OR910870.1 United States Onustus longleyi 24°36’N 82°54’W ANSP 510858 PZ212875 Panama Xenophora robusta 8°25’N 79°06’W The Phase Loop Criterion C. R. Gimarelli (January 10, 2026) \affiliation Independent Researcher Table 2. Average pairwise genetic distances of cox1 sequences between species. Kimura-2-parameter (K2P) distances above the diagonal, simple raw distances (p-distance) below the diagonal. Interspecific distances in bold. Average intraspecific K2P distances along the diagonal. Number of sequences in brackets following species names. 1 2 3 4 5 1. Onustus caribaeus (12) 0.002 0.166 0.182 0.107 0.132 2. Onustus longleyi (11) 0.132 0.002 0.170 0.149 0.173 3. Ponderiana digitata (3) 0.144 0.136 0.007 0.161 0.198 4. Xenophora conchyliophora (16) 0.093 0.122 0.132 0.007 0.141 5. Xenophora robusta (1) 0.110 0.137 0.152 0.116 0.000 Figure 1. Xenophora conchyliophora and their protoconchs. A. Xenophora conchyliophora post-larval juvenile specimen (MNHN-IM-2023-493) B. SEM of protoconch of specimen in panel A. C. Live adult animal from Guadeloupe (MNHN-IM-2019-50025) D. SEM of broken protoconch of X. conchyliophora subadult (UF 568180) E. SEM of protoconch remnant in X. conchyliophora (CM 136747). White arrows indicate positions of the first four attachment scars, arrow marked with “sp” indicates septum plugging opening left by apical loss. Inferred protoconch traced in dotted white line. Scale bars: A = 1.0 mm; B = 100 μm, D = 100 μm; E = 100 μm. Figure 2. Protoconchs of other Xenophoridae. A. SEM of O. caribaeus post-larval juvenile (ANSP 267256) . B. SEM of O. longleyi protoconch (ANSP 193884) C. SEM of X. pallidula protoconch (UMMZ MOE). D-E. SEM of a sculptured protoconch of undetermined species from New Caledonia (MNHN-IM-2019-35061). F. Paucispirality in A. flindersi (WAM S.118706), photo courtesy of Emma Wang . Scale bars: A = 1.0 mm; B = 1.0 mm, C = 1.0 mm; D = 1.0 mm ; E = 100 μm; F = 1.0 mm. Figure 3. Range maps of Western Atlantic Xenophoridae. Pentagram symbol denotes the locality of X. conchyliophora from Guadeloupe (MNHN-IM-2023-493). Inverted triangles mark the locality of the two other specimens with examined protoconchs (UF 568180 and CM 136747). Figure 4. Phylogenetic position of X. conchyliophora . Maximum likelihood phylogenetic reconstruction of the family Xenophoridae in the Western Atlantic and Eastern Pacific species based on cox1 sequences, with P. digitata as outgroup. Branch lengths are proportional to level of molecular divergence. Bootstrap support values provided for interspecific branches. Tree scale for 0.01 substitutions per site. Information & Authors Information Version history V1 Version 1 02 April 2026 Copyright This work is licensed under a Non Exclusive No Reuse License. Keywords comparative evolutionary ecology invertebrate marine molecular genetics natural history sequencing Authors Affiliations Yu Kai Tan 0000-0002-7216-2258 [email protected] University of Michigan-Ann Arbor View all articles by this author Metrics & Citations Metrics Article Usage 170 views 119 downloads .FvxKWukQNSOunydq8rnd { width: 100px; } Citations Download citation Yu Kai Tan. A Paradox: Paucispiral Protoconch in a Widespread Carrier Snail Xenophora conchyliophora. Authorea . 02 April 2026. DOI: https://doi.org/10.22541/au.177514604.48545112/v1 If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download. For more information or tips please see 'Downloading to a citation manager' in the Help menu . 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