2021 年 68 巻 1 号 p. 11-16
The stomiid snaggletooth genus Astronesthes Richardson, 1844 comprises nine species groups (including 40 valid species), plus a further eight species independent of the groups. Among them, the Astronesthes cyanea species group (seven species) is distinguished from all other species by having the following characters: e.g., 42‒50 total vertebrae, 16‒21 dorsal-fin rays, a relatively long chin barbel (but rudimentary in three species), 3 or 4 photophores (part of the ventral row below the pectoral fin) forming an arch, and prominent luminous tissue on the operculum in large specimens. Two specimens (84.6 and 111.1 mm in standard length) belonging to this species group, collected off the Yaeyama and Ogasawara Islands, Japan, were identified as Astronesthes formosana Liao, Chen and Shao, 2006. Although the original description of A. formosana, which noted its close resemblance to Astronesthes indopacifica Parin and Borodulina, 1997, considered the former to differ from the latter in having prominent luminous patch on the lower jaw (vs. absent), a slightly swollen or rounded tip on the chin barbel (vs. slender and simple), prominent luminous tissue on the lower part of the operculum, extending to the lower end of the maxilla [vs. restricted to the middle part of the operculum (in >50 mm standard length specimens)], numerous scalelike spots or prominent patches dorsally on the head and body (vs. sparse), and the upper nostril with more a pair prominent or smearlike luminous patches (vs. a single pair prominent luminous patches), no significant differences were found between the two species in prominent luminous tissue on the operculum, and scalelike spots or prominent patches dorsally on the head (including upper nostril) and body. In addition, the barbel tip shape was found to be of inconclusive value for separating the two species, leaving the presence or absence of prominent luminous patch on the lower jaw as the only valid distinguishing characteristic. Because the features of the two Japanese specimens agreed closely with those in the original description of A. formosana, they were identified as that species, being the first record of the latter from Japanese waters. The new standard Japanese name “Taiwan-tokagegisu” is proposed for the species.