Abstract
A new ophidiid fish, Sirembo quinquefasciatus , is described based on the holotype and 13 paratypes, 125–172 mm in standard length, collected from the southern South China Sea (Gulf of Thailand, off the east coast of Peninsular Malaysia and off the west coast of Borneo). The new species can be distinguished from all other congeners by having two dark longitudinal bands on the anal fin, one along its base, the other submarginal. Furthermore, S. quinquefasciatus sp. nov. differs from Sirembo amaculata (Cohen and Nielsen 1982) and Sirembo wami Nielsen, Schwarzhans and Uiblein 2014 in having several blotches on the dorsal fin (vs. a single dark longitudinal band in S. amaculata and only two blotches in S. wami ). The present new species can be distinguished from Sirembo metachroma Cohen and Robins 1986 by having dark bands along the dorsal-fin base and the lateral line (vs. no band along dorsal-fin base and a distinctive black streak along lateral line in the latter). The new species resembles Sirembo imberbis (Temminck and Schlegel 1846) and Sirembo jerdoni (Day 1888) in sharing many dark blotches on the dorsal fin and several dark longitudinal bands on the body and the anal fin. The former is distinguishable from S. imberbis by having 6–8 scale rows between the dorsal-fin origin and the lateral line (vs. 9–11), and from S. jerdoni by the position of the dorsal-fin origin (above fourth or fifth vertebra vs. first to third).