Diagnosis: Mastacembelus apectoralis differs from all other mastacembelid species by the absence of pectoral fins (Ref. 86808). It is endemic to Lake Tanganyika and is placed within the Lake Tanganyika species flock; it differs from other members of this radiation by a near absence of scales, present only on the margin of the caudal peduncle and between caudal-fin rays, a very short rostral appendage and well-developed adductor mandibulae muscles forming a distinctive head shape; the lack of pigmentation distinguishes this species from all other Tanganyikan species, with the exception of M. micropectus and M. cunningtoni, although the latter species has a distinctive dark spot on the caudal and pectoral fins; both M. apectoralis and its sister species, M. micropectus, lack teeth on the palatine; Mastacembelus apectoralis has 32-34 dorsal spines, and based on this count, is distinguished from five other species in the Lake Tanganyika flock, M. platysoma, M. zebratus, M. polli, M. cunningtoni and M. moorii, which have fewer spines, 21-29; however, all other Lake Tanganyika species have overlapping spine count ranges, 24-38, at least in part with that of M. apectoralis; vertebral counts of M. apectoralis, 77-80, are in the region of those of M. micropectus and M. albomaculatus, are greater than M. zebratus, but are lower than other Tanganyikan species (Ref. 86808).

Description: Body elongate, rounded in cross-section, but with lateral compression in the caudal area; pre-anal and post-anal lengths approximately equal (Ref. 86808). A total of 32-34 dorsal-fin spines, with most/all spines covered entirely by skin and not visible from the outside; three anal-fin spines, the second of which may protrude through skin, with the third spine below the skin surface (Ref. 86808). Well-developed adductor mandibulae muscles form distinct left and right hemispheres in adults; eyes very small, mean diameter 10.9% of head length; lips thick and fleshy, mouth terminal, gape extending posteriorly to vertical through to the anterior edge of the eye; jaws with numerous small pointed teeth; snout broad, with a very short, 9.2% of head length, rostral appendage; pre-opercular and pre-orbital spines absent (Ref. 86808). Body largely scaleless, except for small, thin, circular cycloid scales on the posteriormost caudal area and between caudal-fin rays (Ref. 86808). Dorsal, caudal and anal fins confluent; rounded caudal fin, supported by a single hypural plate probably formed by fused hypurals; pectoral-fin rays, pectoral radials and distal pectoral radials absent, unique within the Mastacembelidae (Ref. 86808). Scapula and coracoid reduced in size and complexity, evident in both juveniles and adults, with a slight left/right asymmetry (Ref. 86808).

Colouration: Largely lacking in pigmentation and patterning; creamish pink or pale yellow in colour, with greyish-purple mesh-like marblings on the head, extending along the dorsum in some spacimens; dorsal, caudal and anal fins pale, often with a darker orange pigment at the base of the fin (Ref. 86808). Colouration is similar in preservation as in life (Ref. 86808).