Homaloptera tateregani Popta, 1905

(Fig. 7)

Homaloptera Tate Reganii Popta, 1905: 180; Popta, 1906: 182, Pl. 10, figs. 40a–b. Homaloptera tate regani – Weber & de Beaufort, 1916: 19.

Homaloptera tate-regani – Hora, 1932: 283, Pl. 11, fig. 4.

Homaloptera tateregani – Kottelat et al., 1993: 53, figs. 135–136. Pseudohomaloptera tateregani – Silas, 1952: 205.

Holotype. RMNH 7632, 63.2 mm SL; East Kalimantan: Mahakam basin, Bo river; A. Nieuwenhuis, May–Aug 1900.

Diagnosis. Homaloptera tateregani differs from its congeners in having the following unique combination of characters: a pronounced groove at each corner of the mouth, just posterior to the maxillary barbel, here termed the postoral groove; eight principal and 12 secondary pectoral fin rays; posterior edge of pelvic fin extending to anal fin origin; scales absent from abdomen; anterior dorsal half of body scales with keel pattern, consisting of mainly one central keel, in some specimens with an additional small keel on either side (Fig. 10 B); 63 scales on the lateral line.

Description. General body shape and appearance as in Fig. 7. For meristics and morphometric data see Table 1. Head elongate, pointed (head width 17.0 % SL; head depth 9.3 % SL). Eye small (eye diameter 14.5 % HL), positioned nearer to opercle edge than to tip of snout, nostril positioned at midway between snout tip and opercle edge. Snout long (snout length 57.2 % HL). Mouth inferior, with three short and fleshy pairs of barbels, two rostral and one maxillary. A pronounced groove just posterior to position of maxillary barbel. Area at ventrum of head covered with many minute raised bumps. Body elongate, laterally compressed, deepest at dorsal-fin origin (body depth at dorsal-fin origin 10.4 % SL), slimmest at caudal peduncle (caudal peduncle depth 5.0 % SL). Body covered with scales, except for naked ventral area. Anus situated just anterior to anal fin origin. Body scales with central keel, sometimes with an additional smaller keel on either side (Fig. 10 B). Anterior and posterior margins of dorsal and anal fins concave. Pectoral and pelvic fins with rounded anterior margin, rounded posterior edge. Caudal fin deeply forked, with lower caudal lobe about 1.24 times that of upper caudal lobe. Vertebrae: 21 + 13, total = 34.

Colour in ethanol. See Fig. 7. The whole specimen appears to be stained reddish brown, probably due to age and/or as an artefact of preservation.

Dorsum and sides of head reddish brown, less pigmented towards ventral margin. Barbels cream. Body dorsally and laterally reddish brown. Dorsum of body with five faint cream narrow bars, marking the interspaces between the six saddle spots; two predorsal, two at dorsal fin base and two postdorsal. Lateral body without discernable body markings. Ventrum cream. Dorsal fin reddish brown, its posterior margin hyaline. Caudal fin cream, with darker brown base, two broad reddish brown bars on upper and lower caudal lobes and middle of fin without distinct bar. Anal fin reddish brown, with posterior margin hyaline. Pelvic and pectoral fins reddish brown, with posterior margins hyaline.

Remarks. See previous treatment for differences between H. tateregani and H. batek . Homaloptera tateregani can be further differentiated from H. stephensoni by the following characters: mouth inferior, with thick fleshy barbels (vs. mouth sub-inferior. with thin barbels); snout long, narrow, with nostril midway between snout tip and opercle edge (vs. snout relatively long, rounded, with nostril nearer snout tip); presence of postoral groove (vs. absence); anus situated just anterior to anal fin origin (vs. between pelvic and anal fin origins); pectoral and pelvic fins falcate (vs. rounded); lower caudal lobe 1.24 times upper caudal lobe (vs. 1.06–1.10); 63 lateral scales (vs. 43–50); more slender caudal peduncle (5.0 % SL, vs. 5.4–6.2); smaller eye (14.5 % HL, vs. 18.3–22.6); larger interorbital width (37.7 % HL, vs. 17.6–21.3).

Distribution. This species is known only from the upper Mahakam River basin in East Kalimantan (Fig. 11).