A new species, Polydactylus siamensis , from Thailand and redescription of P. plebeius (Broussonet, 1782) with designation of a neotype (Perciformes: Polynemidae)

A new species, Polydactylus siamensis, is described on the basis of eight specimens from Thailand. The species is similar to P. plebeius (Broussonet, 1782) in having five pectoral filaments and several dark stripes along the scale rows above and below the lateral line, but differs from the latter in having lower counts of pectoral fin rays (15 vs. 16–18 in P. plebeius), pored lateral line scales (54–58 vs. 60–68), scale rows above and below the lateral line (7 and 10 or 11, respectively vs. 8 or 9 and 12 or 13, respectively) and gill rakers (9 or 10 upper series, 13 or 14 lower and 22–24 total vs. 9–14, 13–18 and 24–32, respectively), and a longer upper jaw (mean 17% [range 16–17%] of standard length vs. 15% [13–16%]). Polydactylus siamensis is currently known only from Bangkok and Songkhla, Gulf of Thailand, and Phuket Island, Andaman Sea, whereas P. plebeius is widely distributed in the Indo-Pacific.