Abstract
Piipironus grandis gen. et sp. nov. is described from Piip submarine volcano, the Bering Sea. Piipironus gen. nov. shows all main characters of Thalassironinae but differs from all known ironids in the form of the amphid (spiral vs pocket-like) and the simultaneous presence of precloacal papilliform supplements and tubular postcloacal organs. Pared tubular postcloacal organs have never been described before for the family Ironidae. The combination of papilliform precloacal supplements and the pair of tubular postcloacal organs described for Piipironus grandis gen. et sp. nov. is unique among nematodes. The study of the nematofauna of the Piip submarine volcano began quite recently, and Piipironus is the second new genus of nematodes described from here from one sample of bottom sediments. This can be taken as one of the examples of the hyper-high diversity of marine nematodes.