First Records of the Brooding Astropectinid Starfish Trophodiscus almus (Echinodermata : Asteroidea) from Japan, with Reference to Its Zoogeographical Significance

抄録

An astropectinid starfish with a unique habit of brooding, Trophodiscus almus Fisher, 1917, has been previously reported to be endemic to the northern part of the Sea of Okhotsk. Recently 11 specimens of this species were obtained from the northern Sea of Japan at depths of 290-295 m off Ajigasawa in Aomori Prefecture, far to the south of the Sea of Okhotsk, and 18 specimens from off Kushiro, Hokkaido, in the Pacific Ocean at depths of 153-252 m. These occurrences of T. almus represent the first records from Japanese waters, and the Sea of Japan is a new southern range limit. A detailed redescription of the species is provided along with color photographs and scanning electron micrographs. The distribution patterns of starfishes known from the Sea of Okhotsk are reviewed in relation to the zoogeographical significance of T. almus.