Relics and antiquity revisited in the modern vent fauna

Abstract A total of 464 species is currently known from hydrothermal vents, with 820eing endemic. More strikingly, endemicity at hydrothermal vents reaches high taxonomic levels with 18 families, 4 superfamilies, 2 suborders, and 1 order endemic. It has been proposed that this magnitude of endemicity is reflective of an ancient, refugial fauna. A review of the many endemic groups reveals that hydrothermal vent communities have mosaic origins. Many endemic groups have recent origins while some appear to reflect ancient faunal elements that have survived in hydrothermal vent refugia. Some may be members of groups surviving refugially throughout the deep-sea while others may have survived refugially in a variety of sulphide-rich habitats, such as hydrothermal vents, hydrocarbon seeps and sunken whale bones. Evolution of sulphide tolerance and especially symbioses with chemoautotrophic bacteria may be threshold adaptations for invasion of multiple sulphide-rich environments. These environments may provide protection from certain causes of extinction. In addition to reviewing current views on endemic taxa, a molecular systematic investigation of the evolutionary origins of vent endemic neomphalinid gastropods is presented.