Ischnomesidae (Isopoda: Asellota) from bathyal and abyssal depths in the Norwegian and North Polar Seas

Abstract

Abstract Ischnomesids are widespread in the deep seas of the world, but they have been little studied in the Arctic. Specimens were collected from the Norwegian Sea during the Norbi expedition in July–August 1975, and during cruises with R.Y. Hõkon Mosby in March, June, and August 1981, and in January and November 1982. Material from the North Polar Sea was obtained during an expedition with the icebreaker Ymer in July 1980. Only four species were found, namely Ischnomesus norvegicus sp.n., Haplomesus quadrispinosus (G.O. Sars), H. ?gorbunovi Gurjanova, and Heteromesus frigidus Hansen. I. norvegicus sp.n. is similar to I. bispinosus (G.O. Sars), but differs in the shape of the male pleotelson, in males having dorsal processes on pereionites 2 and 3, and in setation of pereiopod 1. I. norvegicus was only found at depths between 794 and 860 m on the Norwegian continental slope. H. quadrispinosus was the most common species, found at depths between 794 and 3672 m in the Norwegian Sea, and between 970 and 3270 m in the North Polar Sea. H. ?gorbunovi was found at depths between 1001 and 2941 m in the Norwegian Sea, and between 970 and 1020 m in the North Polar Sea. H. frigidus was found at depths between 800 and 2104 m in the Norwegian Sea, and between 970 and 1020 m in the North Polar Sea.