1980 Volume 27 Issue 3 Pages 215-236
Six species of the genus Bathygobius collected in Japan were compared with each other and with the type specimens of nominal species considered as synonyms of three species of the genus Bathygobius: B.petrophilus, B.scapulopunctatus, and B.fuscus listed by Koumans (1953).
The genus Bathygobius has the following combination of characters: a protuberance below the anterior nostril bordered by a groove containing pit organ line 6 on the upper side and by a groove containing pit organ line 7 on the posterior side, a median longitudinal groove containing pit organ line 10, which runs from the anterior margin of the cheek and divides into two posteriorly, the trapeziform mental flap bordered by a groove containing pit organ line 13 on the lateral side and by a groove containing pit organ line 14 on the posterior side, and free branched rays on the upper part of the pectoral fin.
Six species of the genus Bathygobius were found in Japan, i.e., B. fuscus, B.padangensis, B.cocosensis, B.petrophilus, B.cyclopterus, and B.cotticeps.
The differences between B.fuscus and B.padangensis are the least among the six species.Clearcut differences between them are only in the number of free branched rays on the pectoral fin and in coloration, although there are some specific differences in the number of pectoral fin rays and the angle between the lower and posterior axes of the first pterygiophore of the first dorsal fin. The number of differences between B.padangensis and B. cocosensis and between B.fuscus and B.cocosensis are only slightly greater. Although more differences are found between B.cyclopterus and B. cotticeps than those among the three species mentioned above, both of them have many common characteristics, some of which are specialized and are only found in these two species.
Based on the number of common and distinctive characteristics, the six species are divided into three types: B.fuscus, B.padangensis, and B.cocosensis; B.petrophilus; B.cyclopterus and B.cotticeps.
B.fuscus, B.padangensis, B.cocosensis, B.cyclopterus, and B.cotticeps are found in the tidal zone of rocky beaches, while B.petrophilus is collected near shore on substrates of sand or mixed mud and sand. B.fuscus, B.padangensis, and B.cocosensis are collected north of 35°N, but specimens of B.padangensis and B.cocosensis collected in the northern area of their range are extremely small in number compared with those of B.fuscus.B.petrophilus is collected between 33° and 35°N in Japan, but as the type specimens of Gobius petrophilus and Gobius villosus were collected in Indonesia, it is conjectured that B.petrophilus inhabits southern Japan south of 33°N.
The examination of the type specimens revealed that Gobius poecilichthys should be synonymized with B.fuscus which is different from Mapo fuscus sensu Jordan, Tanaka and Snyder (1913).M. fuscus sensu Jordan, Tanaka and Snyder is presumed to be synonymous with B.padangensis from the description of M.fuscus sensu Snyder (1912a) from Tanegashima, in which the difference between M.fuscus and Mapo poecilichthys was recorded, and from the specimens of M. fuscus sensu Snyder (1912b) from Naha.
Bathygobius sp.reported by Arai and Ida (1975), Zama and Fujita (1977), Hayashi and Itoh (1978) was identified as B.cocosensis on the basis of comparison with three specimens of that species (RMNH 4533) collected and identified by Bleeker.