Diagnosis: Adult male and female Petrotilapia palingnathos have distinctly retrognathous jaws and can thus be distinguished from all other members of Petrotilapia (Ref. 87181). Furthermore, the absence of a dark submarginal band in the dorsal fin distinguishes P. palingnathos from P. microgalana, P. genalutea, P. nigra, P. chrysos, P. mumboensis, and P. pyroscelos, which have such a band (Ref. 87181). Adult males of P. palingnathos are dark gray with orange markings and scales outlined in blue with orange cheek and a blue gular area, which distinguishes them from P. tridentiger, which are light blue with dark blue bars, and from males of P. xanthos which are yellow, while those of P. flaviventris are yellow on ventral and mid-sides with scales outlined in blue (Ref. 87181).

Description: Body depth at origin of dorsal fin 38.0-38.9% of standard length; dorsal head profile concave between snout tip and interorbital (Ref. 87181). Horizontal and vertical eye diameters 23.6-26.2% of head length and 25.6-27.7% of head length, respectively; preorbital depth 24.9-30.8% of head length; snout length 40.5-44.5% of head length; retrognathous jaws and thickened lips; teeth on lower jaw in 18-26 rows with outer and inner rows tricuspid (Ref. 87181). Dorsal fin with XVII-XVIII spines and 8-10 rays; anal fin with III spines and 7-8 rays; first dorsal-fin spine less than half length of eighth spine; caudal fin subtruncate to emarginate; depressed pelvic fin reaching first ray in males; pectoral fin round and paddle-shaped (Ref. 87181). Flank scales large, ctenoid; cheek with 4 rows of scales; lateral line with 30-31 pored scales (Ref. 87181).

Colouration: Live males with orange cheek and preorbital, preopercle, and opercle orange with blue highlights; throat blue; interorbital dark gray with light blue bar; flank dark gray with scales outlined in blue, and with some orange markings, with 8-10 faint vertical dark gray bars; dorsal spines dark blue/gray; blue membrane with orange markings; caudal fin with blue rays and orange membranes; anal fin with faint orange cast and 1-3 yellow ocelli; pelvic fin with yellow to clear membranes and white to light blue leading edge; pectoral fins with brown rays and clear membranes (Ref. 87181). Live colouration for females: overall orange brown colour and 8-10 dark brown vertical bars; dark brown opercle; throat, breast, and belly yellow to orange; dorsal fin without black submarginal band; spines and rays brown with orange lappets and clear membranes; pelvic fin brown with blue leading edge and clear membranes; pectoral fin with brown rays and clear membranes (Ref. 87181). Preserved males with brown head, black opercle, and light brown throat; flank dark brown and without bars; belly and breast brown; dorsal fin without black submarginal band; spines, rays, and membranes gray; caudal fin with dark brown rays and brown membranes; anal fin light brown with 1-3 light brown ocelli; membranes light brown; pelvic fin with light brown spine and rays; membranes clear; pectoral fin with light brown rays and clear membranes (Ref. 87181).