Diagnosis: A smallish laterally spotted haplochromine distinguished from most Otopharynx species by its suprapectoral spot, which is situated entirely below the upper lateral line and separated from it by about half the spot height; this spot is roughly rectangular, longitudinally elongate, 1-1.5 scales high, covering about seven consecutive scales, about three times as long as tall (Ref. 119408). The placement and shape of the suprapectoral spot immediately distinguish Otopharynx mumboensis from O. antron, O. argyrosoma, O. auromarginatus, O. decorus, O. heterodon, O. pachycheilus, O. selenurus, O. speciosus, O. spelaeotes, O. tetraspilus, and O. tetrastigma, all of which have the suprapectoral spot touching or usually extending above the upper lateral line, or may have no suprapectoral spot in O. selenurus; only O. brooksi, O. lithobates, and O. ovatus have a suprapectoral spot similar to that of O. mumboensis (Ref. 119408). Compared to O. brooksi, O. mumboensis has a shorter head, 31-32% of standard length vs. 36-39%, fewer outer teeth in the upper jaw, 47-50 vs. 69-87, and more gill rakers, 13 on lower limb vs. 11-12; compared to O. lithobates, O. mumboensis is deeper bodied, body depth 35.5-36.1% of standard length vs. 29.5-34.4%, has a shorter lower jaw, 35.7-36.2% of head length vs. 36.9-42.0%, and has a lower pharyngeal bone with all teeth of the median columns somewhat enlarged, with subcylindrical shafts and submolariform crowns vs. with slightly enlarged submolariform teeth confined to the posteromedian area; compared to O. ovatus, O. mumboensis has a shorter lower jaw, 35.7-36.2% of head length vs. 43.2-44.3%, larger eye, orbit length 34.8-35.4% of head length vs. 27.9-32.9%, narrower interorbital width, 22.6-24.0% of head length vs. 26.5-29.6%, more triangular lower pharyngeal bone with the posterior contour nearly straight vs. more Y-shaped and rather deeply notched posteriorly, and all teeth in the median columns of the lower pharyngeal bone somewhat molariform, the crowns broadened and flattened vs. the teeth in these columns bicuspid, their crowns not molarized (Ref. 119408).

Description: Deep bodied, body depth 35.5-36.1% of standard length (Ref. 119408). Dorsal profile straight from snout tip to above rear of orbit, evenly rounded from there to end of dorsal-fin base, more convex than ventral profile; premaxillary pedicels not prominent, their angle 42-46°, interorbital angle 42-44°, nuchal angle 16-20°; ventral profile nearly straight from lower-jaw tip to below pectoral-fin base, chest profile inclined about 20° (Ref. 119408). Jaws equal anteriorly, lower jaw not dorsoventrally flattened; lips neither thickened not lobate; gape inclination 39-45°; lower-jaw length-width ratio intermediate, the hemijaws, as seen from below, parallel or diverging and well separated posteriorly; lower-jaw underside angle 34-42°; snout acuteness 71-77°; eyes large, circular, orbit length about 35% of head length; pupil nearly round; eye not reaching dorsal head profile (Ref. 119408). Caudal peduncle 16.1-17.0% of standard length, its length 1.4-1.6 times its depth (Ref. 119408). Dorsal and anal fins rounded posteriorly, without elongated rays; caudal fin shallowly emarginate; pectoral fin 25.6-32.3% of standard length, reaching level of anus (Ref. 119408). Dental arcade in each jaw rounded; upper jaw with 47-51 teeth in the outer row; outer upper-jaw teeth stout, bicuspid, an occasional one tricuspid, crowns slightly recurved with major cusp rounded; last three to four unicuspid or with small shoulder of minor cusp; anterior teeth closely spaced, inclined slightly toward symphysis; outer row of lower jaw of haplochromis type, with 37-40 teeth; teeth similar to those of upper jaw; anterior teeth erect, crowns slightly recurved; many outer teeth of both jaws have crowns broken or heavily worn; inner teeth in two to four rows in each jaw; tricuspid with major cusp often semicircular; inner teeth relatively large although clearly smaller than outer teeth; unusual in that crowns are pigmented red-brown as in outer teeth (Ref. 119408). Lower pharyngeal bone subtriangular, lightly built, dorsoventrally compressed in posterior view; posterior contour nearly straight, slightly emarginate; horns slender, each horn terminating in an L-shaped facet whose caudal flange is autapomorphically elongated into a fingerlike process three to four times as long as its lateral flange; median suture straight to slightly sinuous, without interdigitations; keel short, scarcely descending, its depth nearly equal to its length, strongly convex below; all teeth of median four to six columns enlarged, stouter than more lateral teeth, crowns somewhat molarized, more strongly so in the caudal half of these columns; posterolateral teeth small, laterally compressed, crowded, and bicuspid; teeth in posterior row 36-42; in each median column 9-10; in each oblique row 7-8 (Ref. 119408). Lacrimal bone bearing four neuromasts and five lateral-line pores; lacrimal notch distinct (Ref. 119408). Gill rakers 13 on lower arch; slender, unbranched; a few widely spaced melanophores on each raker (Ref. 119408). Scales ctenoid; 34-35 in lateral line; lateral line discontinuous, upper section with downward kink one to four scales long; squamation extending onto caudal fin between fin rays, to near tips of upper and lower lobes and on basal one-half along middle rays; soft dorsal and anal fins with one to three small scales between bases of some rays; size transition gradual between larger abdominal and smaller thoracic scales (Ref. 119408).

Colouration: Colouration in life of males unknown; a young fish, possibly female, shows the head and body gray to creamy white; each flank scale has a yellow-orange basal spot; melanic markings comprise three prominent midlateral dark spots including a suprapectoral spot about three times as long as high, situated entirely below upper lateral line and separated from it; a supraanal spot about twice as long as high; and a precaudal spot at end of caudal peduncle; a row of three small dark spots above anterior part of upper lateral line, one at the level of hind edge of operculum and others just above lateral line over front and rear of suprapectoral spot; five small dorsal midline spots just below dorsal-fin base; about nine faint, narrow vertical bars below base of dorsal fin; a faint opercular spot; no distinct markings on snout, nape, or fins (Ref. 119408). This melanic pattern essentially identical to that of Otopharynx lithobates, O. brooksi, and O. ovatus; the yellowish scale spots and the dark markings on a larger individual are similar, however, the dorsal midline spots and the spots just above the upper lateral line are darker and more prominent, and indistinct dark marks are present between the midlateral spots; the dorsal fin has pale yellowish lappets and there are yellow oval maculae between the soft dorsal rays; between the caudal-fin rays the membrane is yellow; there appears to be a yellow eggspot in the soft anal fin (Ref. 119408). Colouration in preservative: head and body almost uniformly brown; suprapectoral spot 1-1.5 scales high, covering about seven consecutive scales, below and separated from upper lateral line by about half height of spot; supraanal spot slightly longer than high; precaudal spot at end of caudal peduncle, shaped like supraanal spot; three spots above anterior part of upper lateral line; five dorsal midline spots, evenly spaced, just below base of dorsal fin; traces of vertical bars, too faint to count accurately; head lacking bars or stripes, with an opercular spot; dorsal-fin lappets pale distally, brown proximally grading into poorly defined submarginal dark stripe, dorsal-fin membrane brown overall, with vague maculae between segmented rays; caudal, anal, and pelvic fins brown; anal fin without eggspots or other distinct markings; pectorals hyaline (Ref. 119408).