Challenging deep-sea cosmopolitanism: taxonomic re-evaluation and biogeography of ‘Cythere dasyderma Brady, 1880’ (Ostracoda)

Abstract. Cythere dasyderma Brady, 1880 was described from samples collected from all the world’s oceans during the HMS Challenger expedition in the 1870s. Subsequently, Cythere dasyderma (or Echinocythereis dasyderma, or Henryhowella dasyderma) has been recorded from the Late Eocene to Recent, from Atlantic, Arctic, Indian, Pacific and Southern oceans, and from intertidal to deep abyssal environments. However, even cursory inspection of illustrations from over 50 publications shows that several species have been included in ‘Cythere dasyderma’. Here, all syntypes of Cythere dasyderma Brady, 1880 archived in the Natural History Museum, London have been re-studied. This species is re-described, re-diagnosed and illustrated with scanning electron microscope images. Cythere dasyderma is assigned to Ayressoleberis gen. nov., which is described here. The geographical distribution of Ayressoleberis dasyderma (Brady, 1880) comb. nov. is no longer cosmopolitan, and includes only the type locality in the abyssal southeastern Pacific. Most of the specimens previously identified as Cythere dasyderma, or its synonyms, belong to other trachyleberidid genera (e.g. Henryhowella, Legitimocythere, Pennyella) and not to Ayressoleberis dasyderma comb. nov. A new species of Ayressoleberis, very similar to Ayressoleberis dasyderma comb. nov., is described and illustrated from specimens previously included amongst the syntypes of ‘Cythere acanthoderma Brady, 1880’. These latter specimens were collected from the continental slope of the southwestern Indian Ocean. This new species is left in open nomenclature herein because only two left valves are currently available.