Diagnosis: two pairs of mandibular barbels; adipose fin small; dorsal fin with only 3-4 soft branched rays; at least 50 branched anal fin rays; 13-15 gill rakers on lower part of anterior branchial arch (Ref. 43912).

Description: 9-10 branched pectoral fin rays; anal with iii-iv unbranched and 49-60 branched soft fin rays, number of anal fin rays rather variable from one population to another; 41-43 non-fused vertebrae; 8-9 branchiostegal rays on one side of head; caudal peduncle deeper than long; nasal barbel reaches at least to midway between eye and opercle and at maximum to posterior border of opercle; maxillary barbel rather long and reaches at least to midway along pectoral spine and at maximum to just before its end; inner mandibular barbel reaches at least to posterior border of eye and at maximum to anterior border of opercle; outer mandibular barbel longest and always reaches to about distal end of pectoral spine; inner side of pectoral spine feebly or extremely feebly serrated, in some specimens irregularities on posterior side of spine hardly recognizable as serrations; head rather broad; band of teeth on palatine continuous or narrowly interrupted in middle; snout reaching slightly beyond lower jaw; caudal fin deeply notched with long and pointed fin lobes (Ref. 43912). A peculiar species with a striking reduction of the dorsal fin; P. longifilis is easily distinguished from its congeners by the large number of gill rakers on the anterior gill-arch and by the numerous soft anal fin rays (Ref. 43912).

Coloration: preserved specimens: head and back brown; dark spot above pectoral fin; dark lateral stripe present along lateral line; short dark horizontal stripe starts at base of pectoral spine and ends at level of origin of anal fin; third dark line extends above base of anal; superior border of upper caudal fin lobe sometimes darkly coloured; anal fin border sometimes grey-brown, other fins generally colourless or faintly pigmented at distal margins (Ref. 43912). Live specimens: silvery-white on flanks, with brown longitudinal lines along lateral line and above base of anal fin; belly white; head and back brown; fins uncoloured (Ref. 43912).