A species of Polydactylus that differs from all of its congeners by the following combination of characters: 8 dorsal-fin spines, first spine tiny, second spine very strong (its width more than 5 times of width of remaining spines); 13 second dorsal-fin soft rays; 11 anal-fin soft rays; 12 pectoral-fin rays, its length 22–24% (mean 23%) of SL, posterior tip not reaching a vertical through posterior tip of depressed pelvic fin; 6 pectoral filaments, fourth or fifth filament longest, its length 77–85% (mean 81%) of SL, posterior tip extending slightly beyond caudal-fin base; pored lateral-lined scales 67–75 (mean 71); lateral line unbranched, extending onto upper end of lower caudal-fin lobe; 6 scale rows above lateral line, 8 below; 14 gill rakers on upper limb, 18 on lower limb, 32 in total; occipital profile concave; posterior margin of maxilla extending considerably beyond a vertical through posterior margin of adipose eyelid; depth of posterior margin of maxilla 4–5% (mean 5%) of SL, greater than orbit diameter; well-developed swimbladder present; basal half of third to sixth pectoral filament white, becoming black distally. Polydactylus luparensis can be easily distinguished from all Indo-Pacific congeners by having the black distal half of the third to sixth pectoral filaments (whitish in the latter). Only two other taxa, Polynemus melanochir dulcis Motomura & Sabaj, 2002 and P. melanochir melanochir Valenciennes in Cuvier & Valenciennes, 1831, in the family Polynemidae have the black pectoral filaments (Motomura & Sabaj, 2002; Motomura, 2004b) (Ref. 83753).