Unexpected diversity of Isidoides (Anthozoa: Octocorallia: Isidoidae) revealed by morphology and phylogenomics analysis with descriptions of four new species

Abstract Isidoidae Heestand Saucier, France & Watling, 2021 is a rare octocoral family currently represented by a single genus and species, Isidoides armata Nutting, 1910 recorded in the western Pacific Ocean. The taxonomic status and diversity of Isidoides is unclear, due to the lack of diagnostic taxonomic features and limited taxon sampling. Based on 23 Isidoides specimens obtained from the northwestern to southwestern Pacific, we carried out morphological and phylogenetic analyses to reveal the taxonomic status of new species and develop reliable features for species identification. The 23 specimens could be classified into four well-supported clades by the phylogenomic analysis of ultraconserved elements (UCEs), four groups by 28S rDNA, and two groups by mtMutS-cox1. Integrating morphology and molecular data, we uncovered unexpected diversity of Isidoides composed of the known species Isidoides armata and three new species, viz., I. elegans sp. nov., I. gracilis sp. nov. and I. pseudarmata sp. nov. The morphological analysis showed high intraspecific morphological variation in colony color and the size, shape and arrangement of polyps. By contrast, sclerite forms with their surface sculpturing are more diagnostic features for species identification. Our phylogenetic and species delimitation analyses indicate that UCEs have higher resolution than the nuclear 28S rDNA and the mitochondrial genes mtMutS and cox1 for species discrimination within Isidoidae. ZooBank: urn:lsid:zoobank.org:pub:392485F5-502E-4383-B153-45B167571190 Competing Interest Statement The authors have declared no competing interest. Footnotes The new version has revised the descriptions of species and remade almost all the illustrations. Some of the sclerite plates now better reflect the surface microstructure. In addition, We complemented Species delimitation analysis. We also supplemented and optimized the introduction and discussion. The new version is clearer in structure, richer in data, and more in line with taxonomy in description. Abbreviations used in this paper include - AM - Australian Museum, Australia - BI - Bayesian Inference - ESNZ - Earth Sciences New Zealand (formerly the National Institute of Water and Atmospheric Research) - MBMCAS - Marine Biological Museum, Chinese Academy of Sciences, China - ML - Maximum Likelihood - NCPOR - National Centre for Polar and Ocean Research, India - NIWA - Invertebrate Collection of the National Institute of Water and Atmospheric Research, New Zealand (now renamed the Earth Sciences New Zealand National Invertebrate Collection) - MNHN - Muséum national d’Histoire naturelle, France - SEM - Scanning Electron Microscope - TMAG - Tasmanian Museum and Art Gallery, Australia - UCEs - ultraconserved elements - USNM - United States National Museum, American - YPM - Yale Peabody Museum, American - ZMA - Zoological Museum of the University of Amsterdam, Netherlands