日本初記録のチョウチンハダカ科魚類ソコエソBathytyphlops marionae

抄録

The genus Bathytyphlops Nybelin, 1957, belonging to the deep-sea benthic family Ipnopidae (including five genera and ca. 29 species), presently includes two valid species, Bathytyphlops sewelli (Norman, 1939) (type locality: Arabian Sea) and Bathytyphlops marionae Mead, 1958 (type locality: Caribbean Sea), the latter recorded in tropical to temperate waters in three of the world’s oceans. Bathytyphlops differs from other ipnopid genera by having the following combination of characters: a very large head [head length 21–23 % of standard length (SL)]; minute eyes; no elongated fin rays; and a single developed raker at the angle of the first gill arch. During an extensive trawl survey in the Okinawa Trough in the 1970s, operated by the Fisheries Agency of Japan, three ipnopid specimens (297–322 mm SL) were collected from depths of 750–1380 m, but have not been included in any subsequent ichthyofaunal reports. Recent examination of the specimens revealed them to be B. marionae, being characterized by 13 anal-fin rays (12–14 in B. marionae vs. 16 in B. sewelli), a long well developed raker on the first gill arch, its length 3.1–3.7 % SL (3–5 % SL vs. < 2 % SL), and distinct eyes in larger specimens (vs. indistinct). Although B. marionae has been recorded worldwide in tropical to temperate waters, except in the eastern Pacific Ocean, it has not been reported from Japanese waters, the present specimens therefore representing the first record of the species from Japan. Standard Japanese names for the genus and species, “Soko-eso-zoku” and “Soko-eso”, respectively, were proposed by Miyake and Aizawa (1983), based on four specimens collected off Suriname.