Homaloptera stephensoni Hora, 1932

Hui, Tan Heok, 2009, A new species of hill stream loach (Teleostei: Balitoridae) from Central Kalimantan, with redescriptions of Homaloptera tateregani Popta and Homaloptera stephensoni Hora, Zootaxa 2171, pp. 48-64 : 61-63

Homaloptera stephensoni Hora, 1932

( Figs. 8–9 )

Helgia modesta (non-Vinciguerra)– Popta, 1906: 186.

Homaloptera stephensoni Hora, 1932: 281 , Pl. 11, Fig. 1 ; Chin, 1990: SC-31, Fig. S31; Kottelat et al., 1993: 73, Pl. 24; Chin & Samat, 1995: 29; Martin-Smith & Tan, 1998: 587; Rachmatika et al., 2005: 28; Kottelat & Widjanarti, 2005: 156.

Homaloptera cf. stephensoni – Roberts, 1989: 90, Fig. 70; Parenti & Lim, 2005: 188.

Holotype. ( EAST KALIMANTAN) – RMNH 7633, holotype, 47.6 mm SL; Upper Mahakam basin; A. Nieuwenhuis, Sep–Dec 1896.

(CENTRAL KALIMANTAN) – ZRC 51741, 5 ex., 26.0– 60.8 mm SL; Katingan basin, Mendawai subbasin; stream at buffer zone of Bukit Raya-Bukit Baka National Park. – ZRC 51742, 12 ex., 46.2–68.6 mm SL; Katingan basin, Mendawai sub-basin; Sungei Baha’e, km 64 logging road at buffer zone of Bukit Raya- Bukit Baka National Park. – BMNH 2001.1.15:2671, 1 ex., 87.2 mm SL; Barito basin; Sungei Laung at Desa Maruwei.

( WEST KALIMANTAN) – ZRC 38834, 7 ex., 23.5–41.4 mm SL; Kapuas basin, Sungei Hulu Leboyan at Keluwin.

( SARAWAK) – ZRC 46986, 2 ex., 34.8–43.6 mm SL; Rejang basin, Kapit, Belakin area, Ulu Sungei Anap. – ZRC 39730, 2 ex., 38.4–38.7 mm SL; Tatau District, Bintulu, Sungei Sawi, Ayam tributary.

( SABAH) – ZRC 49169, 3 ex., 32.7–58.6 mm SL; Danum Valley, Sungei Palum Tambun, tributary of Sungei Segama. – ZRC 49170, 3 ex., 51.4–52.0 mm SL; Danum Valley, Sungei Bole Kechil tributary. – ZRC 49172, 5 ex., 41.4–56.5 mm SL; Danum Valley, stream at km 113 on main line west (logging road) after turnoff to Borneo Rainforest Lodge. – ZRC 49174, 2 ex., 45.4–61.7 mm SL; Danum Valley, Sungei Bilong at ca. km 83 on main line west after turnoff to Borneo Rainforest Lodge. – ZRC 49173, 3 ex., 36.5–50.0 mm SL; Danum Valley, stream at km 111 on main line west after turnoff to Borneo Rainforest Lodge. – ZRC 49171, 1 ex., 55.5 mm SL; Danum Valley, Sungei Bole Kechil, km 54 on road to Danum Valley Field Centre. – ZRC 49168, 2 ex., 47.3–54.4 mm SL; Danum Valley, Segama basin, Sepat Kalisun stream. – ZRC 49176, 1 ex., 58.5 mm SL; Danum Valley, Cabin stream right, km 50 on road to Danum Valley Field Centre. – ZRC 49175, 1 ex., 53.0 mm SL; Danum Valley, Sungei Taliwas, km 22 on road to Danum Valley Field Centre. – ZRC 49177, 2 ex., 47.2–56.7 mm SL; Danum Valley, stream at km 105 on main line west after turnoff to Borneo Rainforest Lodge. – ZRC 45487, 1 ex., 42.4 mm SL; Sabah: Segama River.

Diagnosis. Homaloptera stephensoni differs from congeners in the following unique combination of characters: mouth sub-inferior with thin barbels; five principle, 12–13 secondary pectoral fin rays (modally 12); scales absent from abdomen; scales on anterior dorsal half of body with keel pattern, consisting of only one central keel at posterior third of scale ( Fig. 10 C); and 43–50 scales on the lateral line.

Description. General body shape and appearance as in Figs. 8–9 . For meristic and morphometric data see Table 1 . Head elongate, rounded (head width 14.7–16.5 % SL; head depth 9.5–10.8 % SL). Eye relatively large (eye diameter 18.3–23.1 % HL), positioned about midway between snout tip and opercle edge, with nostril positioned nearer to snout tip. Snout relatively long (snout length 46.3–52.3 % HL). Mouth subinferior, with three short and slender pairs of barbels, two rostral and one maxillary. Absence of postoral groove. Area at ventrum of head without bumps or tubercles. Body elongate, laterally compressed, deepest at dorsal-fin origin (body depth at dorsal-fin origin 11.0–14.7 % SL), slimmest at caudal peduncle (caudal peduncle depth 5.4–6.2 % SL). Body covered with scales, except for naked ventrum area. Anus situated midway between pelvic fin origin and anal fin origin. Body scales with central keel at posterior third ( Fig. 10 C). Dorsal and anal fins with straight anterior and posterior margins. Pectoral and pelvic fins with rounded anterior margins, rounded posterior edges. Caudal fin forked, with lower caudal lobe about 1.06–1.10 times that of upper caudal lobe. Vertebrae: 20–21 + 11–12, total = 32–33 [32] (n = 9) (figure in brackets is for the holotype).

Colour in ethanol. See Figs. 8–9 . Dorsal and lateral of head cream, with dark brown blotches, cream or white towards ventral margin. Barbels cream. Dorsal and lateral of body cream. Dorsum of body with five to six dark brown rounded blotches; one to two predorsal, one at dorsal fin base and two postdorsal. Lateral with up to eight dark brown blotches along the lateral line, with larger blotches towards caudal. Ventrum cream or white. Dorsal fin whitish, with two indistinct brown bars. Caudal fin whitish, with cream caudal base, two broad dark brown bars on upper and lower caudal lobes. Anal fin whitish, with one indistinct brown bar. Pelvic and pectoral fins whitish, with two dark brown bars, distinct only at anterior second to third rays.

Remarks. See sections above differentiating H. stephensoni from H. batek and H. tateregani .

Distribution. The type locality of this species is from the upper Mahakam River basin in East Kalimantan; and has also been recorded from Sabah (Tenom – Chin, 1990; Danum Valley – Chin, 1990, Martin-Smith & Tan, 1998), Sarawak (Rejang basin, Ulu Katibas – Parenti & Lim, 2005; Tatau basin - ZRC), West Kalimantan (Sentarum Lakes – Kottelat & Widjanarti, 2005; and Sungai Pinoh – Roberts, 1989), Central Kalimantan (Katingan – present study, and Barito basins – BMNH) and East Kalimantan (Malinau – Rachmatika et al., 2005) ( Fig. 11 ).

Figures

FIGURE 1. Homaloptera batek. Dorsal, lateral and ventral views, ZRC 51743, 98.6 mm SL.

FIGURE 8. Homaloptera stephensoni. Dorsal, lateral, ventral and oral views, respectively, from top, RMNH 7633, holotype, 47.6 mm SL.

FIGURE 9. Homaloptera stephensoni. Dorsal, lateral and ventral views, respectively, from top, ZRC 51741, 58.5 mm SL.

FIGURE 10. Schematised drawings of anterior dorso-lateral body scales of: A, Homaloptera batek, ZRC 51743, 97.2 mm SL; B, H. tateregani, RMNH 7632, 63.2 mm SL; C, H. stephensoni, ZRC 51742, 68.6 mm SL (scale bar = 1 mm).

FIGURE 11. Map of Borneo showing distribution of Homaloptera batek (circle), H. tateregani (triangle) and H. stephensoni (square – solid: type locality, hollow: other locations).