Diagnosis: A small, laterally spotted haplochromine recognizable by the following combination of characters: spots often indistinct, the suprapectoral spot, when discernible, vaguely rectangular, centered on subdorsal bar 3 or connecting bars 3 and 4, and covering four to five consecutive lateral-line scales, extending vertically from just above lateral midline to half a scale above upper lateral line; about seven vertical gray bars below dorsal-fin base; 34-35 scales in lateral line; 11-13 gill rakers on lower limb; 48-73 teeth in outer row of upper jaw; lower pharyngeal bone with a few posteromedian teeth enlarged, submolariform to molariform; lacrimal bone lacking a notch at base of lacrimal process (Ref. 119408). Otopharynx peridodeka is superficially most similar to O. panniculus, which also lacks a lacrimal notch, but O. peridodeka has more scales in the lateral line, 34-35 vs. 31-33, usually fewer lower gill rakers, 11-13 vs. 13-15, posteromedian pharyngeal teeth distinctly enlarged relatively to more lateral teeth vs. median and lateral teeth of nearly uniform size, averages fewer teeth in the posterior row of the lower pharyngeal bone, 37-44 vs. 42-48, and has a deeper lacrimal bone, 19.9-24.7% of head length vs. 18.1-19.9% (Ref. 119408). Compared to O. aletes, O. peridodeka has the hemijaws in ventral view posteriorly convergent, approximated vs. divergent, distant; and lower pharyngeal bone more lightly built, with narrower posterior horns, posteromedian teeth somewhat enlarged but laterally compressed, cuspidate vs. bone heavier, horns thickened, posterior teeth of median rows enlarged, crowns molarized, nearly hemispherical (Ref. 119408). Trematocranus brevirostris is somewhat similar, but in Otopharynx peridodeka the suprapectoral spot is rectangular, covering four to five longitudinal scales, and is located almost entirely below the upper lateral line vs. taller than long, covering three scales and, at least in the lectotype, placed more above than below the upper lateral line; the cephalic lateral-line system is not enlarged vs. pores and canals of the preorbital, nasal, dentary, and lacrimal bones inflated; and there are 48-73 outer upper-jaw teeth vs. about 43 (Ref. 119408).

Description: Moderately deep-bodied, body depth 30.7-35.0% of standard length (Ref. 119408). Dorsal profile of snout straight or slightly convex, head and nuchal profile nearly straight or variably convex, dorsum convexly curved to end of dorsal-fin base; premaxillary pedicels slightly prominent in head profile, their angle 44-57°, interorbital angle 31-40°, nuchal angle 19-25°; ventral profile almost a mirror image of dorsal profile (Ref. 119408). Jaws equal anteriorly, lower jaw slightly flattened dorsoventrally; lips thin and not lobate; gape inclination 26-36°; lower-jaw length-width ratio narrow, the hemijaws, as seen from below, converging toward the rear; lower-jaw underside angle 25-35°; snout acuteness 71-84°; eyes large, orbit length 34.7-38.2% of head length, slightly oval, vertical eye diameter 31.2-35.0% of head length; pupil somewhat pointed anteriorly, rounded posteriorly; eye nearly reaching dorsal head profile (Ref. 119408). Caudal peduncle 18.2-21.0% of standard length, its length 1.7-2.1 times its depth (Ref. 119408). Soft dorsal and anal fins produced, more so in males; caudal fin emarginate; pectoral fin 30.2-40.4% of standard length, reaching at least to the level of first anal-fin spine base and even as far as the base of second soft ray, the length apparently not correlated with sex; pelvic fin 18.6-30.1% of standard length, produced in males (Ref. 119408). Dental arcade rounded in each jaw; upper jaw with 48-73 teeth in outer row; outer teeth closely spaced, larger near symphysis; anterior to lateral teeth unequally bicuspid with long, acutely pointed major cusp, an occasional tricuspid tooth intermixed; about 10-12 posterior teeth unicuspid; outer lower-jaw teeth similar in form to those of upper jaw; those in anterolateral area angled somewhat outward whereas anterior and posterior teeth are more erectly implanted; lower-jaw outer tooth row of haplochromis type, with 41-63 teeth; inner teeth unequally tricuspid, in two to three rows (Ref. 119408). Lower pharyngeal bone subtriangular, somewhat lightly built; posterior contour emarginate, the halves meeting at an obtuse angle, horns moderately long and robust, widening distally; median suture straight to slightly sinuous; keel slightly descending, longer than deep, strongly convex below; bone of moderate depth in posterior view; several posteromedian teeth variably enlarged; lateral pharyngeal teeth small, bicuspid; teeth in posterior row 37-44; in each median column 7-12; in each oblique row 5-8 (Ref. 119408). Lacrimal bone bearing four neuromasts and five lateral-line pores; lacrimal notch obsolete (Ref. 119408). Gill rakers 11-13 on lower arch, rather short; few melanophores (Ref. 119408). Scales ctenoid; 34-35 in lateral line; lateral line discontinuous, upper section with downward kink three to five scales long, or kink lacking; squamation extending onto caudal fin between fin rays, to near tips of upper and lower lobes and on basal one-fourth along middle rays; soft dorsal and anal fins with two to three series of small scales between bases of some rays; larger scales of lower flanks transition gradually to smaller chest and belly scales between pectoral- and pelvic-fin bases (Ref. 119408).

Colouration: Colouration in life is unknown (Ref. 119408). However, a fresh male and female identified as Otopharynx "brevirostris deep", thought to belong to this species, are gray dorsally, silvery on flanks, white on belly, chest, and head below eye; six gray bars below dorsal-fin base; indistinct gray suprapectoral, , supraanal, and precaudal spots; unpaired fins of male yellowish, dorsal with black lappets and orange maculae between spines and rays; pelvics yellow, those of male with distinct black leading edges; pectorals hyaline (Ref. 119408). Colouration in preservative: brown on dorsum and upper head surfaces; lower flanks silvery, grading to white ventrally on belly and sides of chest; operculum silvery with dark spot; dark brown spot on upper part of lacrimal; lower jaw, gular region, and branchiostegal membrane dark brown; ventral chest surface light brown; seven narrow gray vertical bars below dorsal-fin base; two bars on caudal peduncle; suprapectoral spot brown, darker than vertical bars; supraanal and precaudal spots indistinct; no dorsal midline spots; dorsal fin with whitish lappets; submarginal fin area brown; anal fin pale brown with no markings evident; caudal fin brownish; pelvics and pectorals hyaline (Ref. 119408).