Amended generic classification of the marine gastropod family Phenacolepadidae: transitions from snails to limpets and shallow-water to deep-sea hydrothermal vents and cold seeps

Abstract Benthic invertebrates at deep-sea hydrothermal vents and cold seeps have attracted considerable attention regarding their spatiotemporal distributions, colonization pathways, geological origins and morphological, ecological and physiological adaptations. Here we first reconstruct a molecular phylogeny for vent and seep species in the gastropod subclass Neritimorpha based on combined mitochondrial and nuclear gene sequences. The resulting tree, in conjunction with anatomical and palaeontological evidence, indicates that neritimorph snails and limpets in the Cenozoic deep-sea chemosynthetic habitats belong to the monophyletic subfamily Shinkailepadinae (family Phenacolepadidae). Confamilial shallow-water species form its sister clade, the subfamily Phenacolepadinae. There were probably at least three independent shifts from the coiled snail with a functional operculum to the limpet form in the evolutionary history of the family, twice in the deep-sea Shinkailepadinae and once in the shallow-water Phenacolepadinae. Physiological and ecological characteristics including the presence of red blood cells and larval migration seem to have facilitated their early Cenozoic colonization of vents and seeps. The type specimens of type species were investigated for most nominal genera to amend generic classification of this long-neglected family. A monotypic Divia gen. nov. is proposed for ‘Shinkailepas’ briandi; Shinkailepas and Thalassonerita pre-date Olgasolaris and Bathynerita, respectively.