ARCTIC SEA-ICE NEMATODES (MONHYSTEROIDEA), WITH DESCRIPTIONS OF CRYONEMA-CRASSUM GEN-N, SP-N AND C-TENUE SP-N

Arctic sea ice presents a habitat to nematodes living in the lacunary system close to the undersurface of the ice. Only members of the Monhy steroidea have been encountered as yet, and it appears that these nema tode species are confined to the ice habitat. In collections from the Fram Strait, near Greenland, and the Laptev Sea, off Siberia, we redis covered Theristus melnikovi Tchesunov, 1986, previously described from the Central Arctic Ocean. Cryonema crassum gen. n., sp. n. and Cryone ma tenue sp. n. were collected off Siberia; juveniles of Cryonema spp. have also been found in the Fram Strait. The new genus Cryonema is cl osely related to;he genus Gammarinema and to similar genera which occu r in association with crustaceans, e.g. in the gill chambers of land c rabs, and to Odontobius cati, an inhabitant of the baleen of whales. T he tail tip of Cryonema contains an internal funnel-like structure, po ssibly part of a closure mechanism for the caudal glands; similar stru ctures have been observed in some other related genera. Many ice nemat odes show an empty intestine; sometimes single protist cells or granul ar substances were observed. Cryonema crassum may feed on small nemato des.