Revision of the cosmopolitan deep-sea genus Sciadonus (Teleostei, Bythitidae) with two new species

The genus Sciadonus Garman, 1899 belongs to the aphyonid clade within the Bythitidae. The present revision is based on 304 specimens all trawled at great depths (1169-5610 m), 19 of which have not been examined earlier. As a consequence, the generic diagnosis from Nielsen et al. (1999) is here modified. The enlarged material resulted in synonymizing of S. galatheae (Nielsen, 1969) and S. pedicellaris Garman, 1899 and in the description of two new species, S. robinsi and S. longiventralis. The new species differ from the other Sciadonus species by lack of pigmentation, fewer dorsal fin rays and position of origin of anal fin. S. longiventralis differs from S. robinsi by shorter predorsal length (28.5 vs 42.5% SL) and length of pelvic fin rays (3.5% SL vs no pelvic rays).