Diagnosis: Haplochromis antleter belongs to an assemblage of small sized (less than 9 cm standard length), relatively deep-bodied (body depth larger than 35% of standard length) micrognathic species with a moderately curved to straight dorsal head profile; the fish in this group have relatively small, mainly bicuspid, teeth in the oral jaws (Ref. 85523). It can be distinguished from Haplochromis cinctus, Haplochromis paropius and Haplochromis katunzii by live colouration of sexually active males: Haplochromis antleter is dusky coloured with no or faint vertical bars and it is the only species of this assemblage that has no or a faint lachrymal stripe; H. paropius has a red dorsum and a greenish flank with faint vertical bars; in contrast to the other three species H. paropius often has a mid-lateral band; H. cinctus has a red dorsum, an orange to yellowish flank and dark vertical bars; H. katunzii is sandy-brown and has, compared to H. antleter, more distinctive vertical bars (Ref. 85523). Haplochromis antleter has a shallower cheek depth, 16.1-21.1% of head length, than H. katunzii and H. paropius, 18.6-24.6% of head length and 18.1-24.2% respectively; and the interorbital width is smaller, 19.1-24.9% of head length, than in the type-specimens of H. cinctus, 24.3-27.2% of head length (Ref. 85523). Compared to H. katunzii, H. antleter has a less pronounced mental prominence on the lower jaw (Ref. 85523).

Description: Body relatively deep; dorsal head profile moderately curved, rarely straight; premaxillary pedicel not interrupting the profile (Ref. 85523). Mouth slightly oblique; lips not thickened; medial part of the premaxilla not expanded; caudal part of the maxilla not bullate; the vertical through the caudal tip of the maxilla runs through the ligamentous ring around the eye, sometimes it runs through the iris; lateral snout outline isognathous and obtuse; jaws equal anteriorly; mental prominence not pronounced; retro-articular processes of right and left mandible generally not touching each other, not interrupting the ventral body outline; eye approximately circular; a small aphakic aperture may be present; cephalic lateral line pores generally not enlarged (Ref. 85523). Cheek, gill cover, dorsal head surface, chest, greater part of dorsum and caudal fin base covered with cycloid scales, the remaining part of the body with ctenoid scales; a gradual size transition between scales of chest and flank; 4.5-6.5 scales between the upper lateral line and the dorsal fin origin, 4.5-7 between the pectoral and the pelvic fin bases (Ref. 85523). Pelvic fins reach the rostral-most point of the anal fin origin, in some specimens extending further; first soft rays of pelvic fins produced and filamentous in some specimens; anal fin just reaching caudal fin origin; caudal fin outline truncate to emarginate (Ref. 85523). The number of gill rakers on the lower part of the gill arch is 10; the lower one to three rakers are reduced; the next four to five rakers are short to normal in size; tip blunt to acutely pointed; the remaining rakers are blunt and diamond-shaped or weakly bifid; the rakers are generally not touching each other; the number of gill filaments ranges from 85 to 89 (Ref. 85523). Premaxillary dentigerous arm about as long as ascending arm; the angle between the two arms is 86° to 91°; a small symphyseal articulation facet can be present; lower jaw slightly elongated; the upper half of the dentary has a moderate to distinct outwardly directed flare; mental prominence slightly pronounced, which is not visible in intact specimens (Ref. 85523). Teeth in the rostral 2/3 of the dentigerous area of both jaws generally unequally bicuspid, occasionally with a few tricuspids or weakly bicuspids among them; caudally tricuspids, weakly bicuspids or blunt unicuspids can be found; the caudal-most two to three teeth of the premaxilla are stout, generally blunt unicuspids or weakly bicuspids, sometimes tricuspids; in bicuspid teeth, the major cusp is subequilateral, often slightly protracted; a small but distinct flange is present, which is less clearly visible in caudally positioned teeth; the cusp gap is wide, the minor cusp is distinct; in labial view, the neck is moderately slender to stout, the crown slightly expanded; in lateral view, the crown is compressed; the premaxillary outer row teeth are recurved, those of the lower jaw slightly recurved; the inner row teeth in both premaxilla and lower jaw are tricuspid; teeth are relatively small and slender (Ref. 85523). Dental arcade rounded and U-shaped; premaxilla generally two, occasionally three inner rows anteriorly, none posteriorly; lower jaw two inner rows anteriorly, none posteriorly; there are 45-57 teeth in the outer row of the upper jaw; premaxillary teeth closely to widely and regularly set, lower jaw teeth closely set; outer row teeth of premaxilla erect, inner row teeth recumbent; lower jaw outer row teeth slightly procumbent, inner row teeth erect (Ref. 85523). Lower pharyngeal element as long as it is broad, or slightly longer than broad; the dentigerous area is distinctly broader than long; the suture is straight; pharyngeal teeth 34-39 in the caudal-most transverse row, 11-12 in medial length rows; teeth in caudal-most transverse row hooked, major cusp only slightly incurved and blunt; other teeth pronounced or bevelled; all teeth are relatively fine and slender, medial teeth not coarser than other teeth (Ref. 85523). The total number of vertebrae is 28-30, comprising 12-13 abdominal and 16-17 caudal vertebrae (Ref. 85523).

Colouration: live colouration of males: snout, dorsal head surface, interoperculum, cheek and gill cover dusky with bluish sheen; the eye has a dark grey outer ring and a light yellowish inner ring; lips are greyish with an iridescent turquoise flush; lower jaw grey to dusky; rostral part of the dorsum and flank dusky, with a caudal increasing blue-turquoise to greenish iridescent sheen; belly, chest, and ventral side slightly lighter than dorsum and flank; the iridescent sheen on the body varies in intensity; nostril-, lachrymal-, supra-orbital stripe and nape band if present, faint; opercular blotch present; three to five faint vertical bars may be present on the flank; pectoral fins hyaline with dusky rays, pelvic fins black; anal fin with a black base, rostro-ventral part wine-red, dorsocaudal part hyaline with two yolk-yellow egg dummies surrounded by a dusky ring; caudal fin with a dusky base, the remaining part wine-red; dorsal fin dusky, with wine-red maculae on the caudal part; lappets rostral dusky, caudally some red zones (Ref. 85523). Preserved colouration of males: entire body dark brown, ventral side slightly lighter; pectoral fins brownish-hyaline, pelvic fins black; anal fin brownish with a dusky base and a more hyaline distal part; caudal fin brownish with a dark base and a dark medial part; dorsal fin and lappets dusky; no, or very faint vertical bars visible (Ref. 85523).