Deep-sea nematodes (Nemata, Prochaetosomatinae): new taxa from hydrothermal vents and a polymetallic nodule formation of the Pacific (East Rise; North Fiji and Lau Basins; Clarion-Clipperton fracture zone)

Dinetia nycterobia gen, et sp. n. (Draconematidae, Prochaetosomatinae) is described from a hydrothermal site of the East Pacific Rise. The new genus is characterized by body annulation reaching lip region and including spiral amphids, cuticle not thickened in head region, cephalic adhesion tubes without expanded base located in cervical region, pharynx with terminal bulb provided with a thick cuticularized lumen wall, and posterior adhesion tubes with bell-shaped end. Dinetia nycterobia, the type species, is characterized by the number of cephalic adhesion tubes (19 in male, 15 in female) and of the 4 rows of posterior adhesion tubes (5 tubes lateral, 14-19 subventral in male, 10-15 lateral, 13-20 subventral in female) and the shape and size of the spicules. Cephalochaetosoma pacificum notium subsp. n. from the Fiji deep-sea closely resemble C. pacificum pacificum from Philippines deep-sea but differs in male by the number of sublateral posterior adhesion tubes, the shape and size of the spicules, the number of cloacal setae, the structure of the testis and in both sexes by the spiny cuticular ornamentation, the shorter labial setae and morphometric data. A new genus and new species of Draconematidae is provisionally described, based on the observation of juvenile specimens from the polymetallic nodule formation.