Considerations on the Taxonomic Status of the Lancelets of the Genus Branchiostoma From the Japanese Waters

With Text 7 figures 1-5 and Tables 1234Introducton The lancelets are generally called by Japanese "Namekuji-uo" (Namekuji=slung, uo=fish); at the same time, however, this Japanese name has been applied also to the single species usually referred to Branchiostoma belcheri (Gray, 1847) since about 1922 when the taxonomic discussions on Japanese 1ancelets were seemingly closed as seen in the historical paragraph of the present paper.The inclusion of all Japanese lancelets in the same single species may be acceptable only when some differences found among the specimens of "N amekuji-uo" from different localities in this country are recognized to be of the intraspecific variation.On the other hand, the lancelets from Kiaochow Bay on the southern coast of Shantung Peninsula, North China, were distinguished as a distinct variety in 1936 from the typical form of B. belcheri, further it was found that this variety was related closely to the "Namekuji-uo" occurring generally along the Japanese coasts except the west coast of Kyusyu Island.Evidently, this seems to request the detailed taxonomic re-examination of Japanese lancelets.The study will need a number of specimens from different localities in this country.Unfortunately, however, "Nameku,ji-uo" has been becoming rapidly rarer and rarer in Japan in these days, though it ever occurred in some waters so richly that it was taken as a kind of sea foods as well as in China-this is the story when the coastal water was still clean in this country.Thus, it was urged to collect large material from localities as many as possible.The efforts payed by the present author for several years brought here the material consisting of more than 150, inclusive of 15 "giant larvae" and a considerable number of specimens from Amoy.The present material can never be satisfactory, but seemingly this might be the limit of efforts to the present author in these days when the coastal waters are affected heavily by pollution in this country and "Namekuji-uo" is disappearing from the former localities recorded.Thus, in this paper it is planned to give the results of close 1) Contributions from the Seta Marine Biological Laboratory, No. 672.