Pamphorichthys pertapeh is distinguished from all other Poeciliinae species by two derived

characters, unique among poeciliins: (a) bilobed teeth present on dentary and external tooth row of the premaxilar bone and (b) distal-most segments of the anterior branch of the fourth gonopodial ray and of the third gonopodial ray are independently fused into elongated segments. Other diagnostic characters that are also found in other species of the tribe Poeciliini are: dark longitudinal stripe on female caudal peduncle; urogenital region of females with heavy dark pigmentation; third pelvic-fin ray of males curved distally; and specialized pair of anal scales anterior to the urogenital opening in females (Ref. 79603).

Dorsal-fin rays i(7) or ii(10)-7(15) or 8(2) (males), i(6) or ii(9)-7(14) or 8(1) (females); anal-fin rays in females iii(15)-9(15); pelvic-fin rays 5(5); caudal-fin branched rays 11(3); unbranched superior caudal-fin rays 6(1) or 7(1); unbranched inferior caudal-fin rays 6(2); pectoral-fin rays 10(1) or 11(2) (Ref. 79603).