Pelagic Amphipods, Infraorder Physosomata (Crustacea : Amphipoda : Hyperiidea) from the CSK International Zooplankton Collection (western North Pacific), with the Description of Four New Species of Scina

Abstract

Physosomata were poorly represented in the CSK (Cooperative Study of the Kuroshio and Adjacent Regions) collections as samples were restricted to the upper 150m and most Physosomata are deep-water species. Nineteen species were identified, all belong to the family Scinidae and, except for Acanthoscina birsteini, the genus Scina. The collection is remarkable in that four of the species are new to science and another ten are new records for the western North Pacific. An annotated list of species is given, the new species are described and a newly constructed key to the world species of Scina is provided. This study concerns the hyperiid amphipods of the infraorder Physosomata collected by the CSK (Cooperative Study of the Kuroshio and Adjacent Regions) during 1965-74. The general area surveyed in the western North Pacific ranged from the Timor, Arafura and South China Sea to just east of .Japan. Further details concerning the CSK International Zooplankton Collection are given by Chuang (1977), Kubota (1984), Motoda (1980) and Yamazi (1971). Previous records of Physosomata from the western North Pacific are given by Bulycheva (1955), Vinogradov (1957) and Yoo (1971). In all, 35 species in 12 genera representing all 7 families have been recorded from this general area. In the CSK collections Physosomata were rare probably because the collections were restricted to the upper 150m and most Physosomata are deep-water species (Vinogradov, 1957). Of the 2, 749 plankton samples, containing hyperiid am phi pods, examined, only 169 contained Physosomata resulting in 202 specimens. All belong to the family Scinidae. I have determined 19 species; Acanthoscina birsteini and 18 species of Scina including 4 species new to science. Apart from the new species the following are new records for the general area surveyed, Acanthoscina birsteini, Scina damasi, S. excisa, S. inermis, S. marginata, S. nana, S. oedicarpus, S. similis, S. stenopus and S. tullbergi. Of the four new species that I describe here three are small (2.0 mm or less) but appear to be fully developed specimens with clear, distinctive features. The discovery of these new species of 2.0 mm or less is not surprising as some species of Scina attain