Biogeography of deep-sea wood fall, cold seep and hydrothermal vent Ostracoda (Crustacea), with the description of a new family and a taxonomic key to living Cytheroidea

Stimulated by finding a novel cytheroid ostracod in a piece of sunken wood retrieved from the sea-bed in the Kuril–Kamchatka Trench, we have reviewed all previously published data on ostracods from similarly ephemeral deep-sea habitats (wood falls, hydrothermal vents and cold seeps). These data are placed in the context of all data on living, deep-sea ostracods from other environments. We confirm previous authors׳ conclusions that faunas from these ephemeral habitats are similar at the generic level, and include elements common to shallow and deep habitats. However, at the species level, endemism varies from zero at cold seeps, to 35% in wood falls and 60% at hydrothermal vents, which is an indication of the relative longevity of these habitats. Non-endemic species occur also in oligotrophic, deep-sea sediments but not in shallow environments. This is in contradiction to previous assumptions that these ephemeral faunas share more species and with shallow habitats than genera with the oligotrophic, deep-sea sediments. We agree with previous authors that the dispersal strategy of wood fall, vent and seep ostracods includes hitchhiking and we propose that it also includes the ability to survive ingestion by larger, more motile animals. The homogeneity of the faunas from ephemeral habitats collected off the American continent is in stark contrast to the highly endemic fauna found in Northwestern Pacific. This suggests that the ostracods may have biogeographical patterns similar to those previously proposed for other groups of benthos. However, any proposal for a global biogeographical scheme for ostracod distributions will have to await far more comprehensive coverage from presently unstudied regions.

Finally, we describe and name a novel species of ostracod from the wood fall collected at a depth of 5229 m in the abyss east to the Kuril–Kamchatka Trench, Northwestern Pacific; erecting a new family Keysercytheridae fam. nov. and a new genus, Keysercythere gen. nov., to accommodate it, and name it, Keysercythere enricoi sp. nov. We present a preliminary key to all Cytheroidea families for which living representatives have been described.