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Dorsal spines (total): 0-0; Dorsal soft rays (total): 9-10; Anal spines: 0-0; Anal soft rays: 18-20; Vertebrae: 33-35. Diagnosis: This species is distinguished from congeners by the possession of 21-24 scales in the longitudinal series vs. 28-42 scales, and from Brachypetersius altus by the possession of a short, abridged lateral line of 6 or 7 pored scales vs. a complete lateral line of 20-28 pored scales (Ref. 91757). Unique among related taxa in displaying marked sexual dichromatism, and dimorphism of the anal-fin skeleton; with medially expanded first anal-fin pterygiophores, markedly enlarged branched anal-ray segments, and strongly convex anal-fin profiles characterizing males; they also display a distinctive black blotch extending from just above midline behind the dorsal fin and passing ventrally over the anal fin (Ref. 91757).
Description: Small-sized species; relatively deep-bodied, particularly in mature males, body depth 32.0-37.6% of standard length, greatest depth at vertical through insertion of pelvic fin (Ref. 91757). Head length 26.4-29.9% of standard length; eye large, bony orbit diameter 36.1-39.9% of head length; dorsal head profile gently convex from upper lip to nape, steeply convex from that point to dorsal-fin origin; dorsal body profile slightly concave along dorsal-fin base, gently convex to caudal-fin base; ventral body profile convex between isthmus and anal-fin base; caudal peduncle usually slightly longer than deep (Ref. 91757). Mouth terminal, lower jaw prominent and slightly prognathous; premaxilla with 2 teeth in outer row, each bearing 3 cusps, positioned opposite interspaces between and alternating with, 4 inner row teeth, each bearing 5-7 cusps; dentary with 4 teeth in outer row, each bearing 8 cusps, 2 small, unicuspid inner row teeth situated at jaw symphysis (Ref. 91757). Dorsal fin with 2 unbranched and 7-8 branched rays, anal fin with 3 unbranched and 15-17 branched rays; origin of dorsal fin slightly in advance of vertical through pelvic-fin insertion (Ref. 91757). Body covered with large, regularly imbricate scales; pored scales of lateral line reduced to 6 or 7 anterior scales; 21-24 scales in longitudinal series to caudal flexion, 4.5 scale rows between lateral line and dorsal-fin insertion, 2.5 between lateral line and pelvic-fin insertion, 10 circumpeduncular scales (Ref. 91757). Thirteen or 14 elongate gill rakers arrayed along lower limb of first arch (Ref. 91757). Total vertebral count 33-35 (Ref. 91757).
Colouration: In alcohol base body colouration pale cream with brown basal crescents present at contact zones of contiguous scales, particularly evident on dorsum and along midline but extend over flanks in larger specimens of both sexes; dorsum of head dark brown; same as distal portion of adipose fin (Ref. 91757). In life, iridescent silver with greenish-copper reflections posterolaterally on flanks and caudal peduncle; in males black blotch evident only at base of anal fin and over body of fin; distal margin of anal fin strongly contrasted in white; in females black blotch visible only over caudal peduncle and along anal-fin base (Ref. 91757). |
