Diagnosis: A medium-sized, laterally spotted haplochromine distinguishable from all previously described Otopharynx species by its more elongate body, its depth 24.3-28.6% of standard length; the next-most-elongate species are Otopharynx decorus, depth 29.4-33.3% of standard length, and O. lithobates, depth 29.5-34.4% of standard length; all others have a body depth larger than 31% (Ref. 119408). Otopharynx styrax is further separated from O. decorus by its longer caudal peduncle, length/depth 2.0-2.3 vs. 1.5-1.6 in O. decorus, and its narrower lower pharyngeal bone, the lateral edges of the horns diverging at about 70° vs. 79-87° in O. decorus; it is further distinguished from O. lithobates by the absence of dark spots on the dorsum below the dorsal-fin base vs. 4-6 distinct dorsal midline spots in O. lithobates, and longer caudal peduncle, length/depth 2.0-2.3 vs. 1.3-1.7 in O. lithobates (Ref. 119408).

Description: Body elongate, its depth 24.3-28.6% of standard length (Ref. 119408). Head sharply pointed in lateral view and narrowly rounded in dorsal view; dorsal profile evenly convex from tip of snout to end of dorsal-fin base, except snout profile nearly straight in some individuals; premaxillary pedicels not prominent, their angle 34-50°, interorbital angle 27-38°, nuchal angle 15-25°; ventral profile varying from a virtual mirror image of the dorsal profile, to less convex and with an almost straight lower head and chest profile (Ref. 119408). Jaws equal anteriorly or lower jaw slightly projecting, lower jaw somewhat dorsoventrally flattened; lips not thickened or lobate; gape inclination 10-30°; lower-jaw length-width ratio narrow, the hemijaws, as seen from below, converging toward the rear and nearly touching posteriorly; lower-jaw underside angle 10-30°; snout acuteness 65-76°; eyes large, elliptical, orbit length 34-38% of head length, about 25% longer than vertical eye diameter; pupil pointed anteriorly, rounded posteriorly, eye reaching dorsal head profile, or nearly so (Ref. 119408). Caudal peduncle 18.6-20.9% of standard length, its length 2.0-2.3 times its depth (Ref. 119408). Soft dorsal and anal fins pointed but short posteriorly; fin spines slender, delicate, flexible; caudal crescentically emarginate; upper and lower lobes acutely pointed, subequal; pectoral fins short, 26.2-30.9% of standard length, acute, reaching level of anus; pelvic fins shorter than pectorals, 20.6-22.1% of standard length (Ref. 119408). Dental arcade narrowly arched in each jaw; upper jaw with 49-64 teeth in outer row; anterior teeth subequally bicuspid, lateral to posterolateral teeth mostly unequally bicuspid, a few posterior teeth unicuspid; outer row of lower jaw of haplochromis type, with 46-57 teeth; anterolateral teeth angled outward, procumbent, anterior teeth with shafts angled toward dentary symphysis; with jaws closed, anterior and anterolateral teeth of lower jaw lie outside upper-jaw teeth, but lateral and posterior teeth are inside those of upper jaw; inner teeth of both jaws unequally tricuspid with middle cusp longest, acute, crowns lightly or not pigmented, arranged in two to three rows (Ref. 119408). Lower pharyngeal bone Y-shaped, narrow, rather lightly built; posterior contour deeply emarginate, each half slightly convex, the halves meeting at an obtuse angle; horns moderately long, slender, of uniform diameter; median suture nearly straight; keel short, straight, moderately deep, convex below; bone moderately deep in posterior view; teeth in lateral fields small, closely set, laterally compressed and cuspidate, but six to nine posteromedian teeth enlarged, their crowns molarized but retaining a posterior cusp; teeth in posterior row 37-45; in each median column 9-10; in each oblique row 5-7 (Ref. 119408). Lacrimal bone bearing four neuromasts and five lateral-line pores; lacrimal notch distinct (Ref. 119408). Gill rakers 11-13 on lower outer arch; slender, unbranched; lacking melanophores (Ref. 119408). Scales ctenoid: 36-39 in lateral line; lateral line discontinuous, upper section with downward kink one to four scales long, or kink absent; caudal fin scaled to near tips of upper and lower lobes and on basal one-half or more along middle rays; soft dorsal and anal fins with a few small scales between bases of some rays; large scales on lower flanks abruptly transition to much smaller scales on chest along a line between pectoral- and pelvic-fin bases (Ref. 119408).

Colouration: Colouration in life of subadult and adult males: dark blue on dorsum and upper head surface, paler blue on sides of head and flanks, whitish on belly; longitudinally elongate, blackish suprapectoral and supraanal spots and nearly circular precaudal spot variably present, probably dependent on emotional state; no dorsal midline spots; seven or eight faint gray vertical bars visible below dorsal-fin base; dorsal-fin lappets white, fin otherwise blue with orange maculae in both spinous and soft sections; caudal fin blue with yellow or orange maculae; anal fin blue with narrow orange distal margin and one to three series of pale yellow eggspots, third row on distal fin margin apparently only in largest males; pelvic fins white to pale blue with white leading edge; pectorals hyaline (Ref. 119408). Females in life appear grayish tan on dorsum, silver on sides of head, silvery with bluish tinge on flanks, white on belly and underside of head; three lateral spots visible but indistinct; dorsal fin shows orangish oval maculae between all spines and soft rays; anal fin hyaline with faint orange flush distally; caudal fin plain yellowish; pelvics white flushed with orange; pectorals hyaline (Ref. 119408). Colouration in preservative: head and body light silvery brown, slightly darker on dorsum and upper head surfaces; no stripes or bars on head; lips yellowish; a vague opercular spot in some specimens; belly pale yellowish silver; lateral spots faint, brownish; suprapectoral spot generally more distinct than supraanal and precaudal spots; no dorsal midline spots; nape with indistinct brown spot above operculum; dorsal fin yellowish, marbled with gray posteriorly; anal fin yellowish with indistinct darker margin; caudal fin yellow with faint maculae; pelvics yellow, shading to brownish distally; pectorals yellow (Ref. 119408).