2023 年 28 巻 1 号 p. 15-22
Ricuzenius toyamensis Matsubara and Iwai, 1951 was originally described on the basis of eight specimens collected from Toyama Bay, the Sea of Japan coast of central Honshu Island, Japan. The species has subsequently been considered as a valid species of the genus Icelus Krøyer, 1845, diagnosed by the following characters: supraocular and parietal spines absent; nuchal spine blunt and indistinct, covered with skin; uppermost preopercular spine unbranched; mid-sized scales scattered (not in rows) above and below lateral line; belly naked; minute ctenoid scales on upper part of maxillary; lateral line scales large, tubular, bearing spinules on dorsal and posterior margins; and lower jaw slightly protruding anteriorly. However, examination of the type specimens of Icelus rastrinoides Taranetz in Schmidt, 1935, a northern Sea of Japan species, showed them to be consistent with the holotype and paratypes of I. toyamensis. Accordingly, I. rastorinoides is regarded as a senior synonym of I. toyamensis, with the lectotype of the former being designated herein. The species is redescribed in detail on the basis of the types of both nominal species plus non-type specimens, with a note on geographic variations in dorsal- and anal-fin ray counts, which reflect Jordan’s rule.
