Engkaria, Hui, 2021

Hui, Tan Heok, 2021, Hypergastromyzon revisited, with descriptions of a new genus and two new species (Teleostei: Gastromyzontidae), Raffles Bulletin of Zoology 69, pp. 336-363 : 352-353

Engkaria , new genus

Diagnosis. A gastromyzontine loach with head and body relatively wide and depressed (body depth at dorsal-fin origin 14.1–16.2% SL, body depth 11.2–13.1% SL, caudalpeduncle depth 7.3–8.5% SL); pectoral and pelvic fins greatly enlarged (pectoral-fin rays 21–25, pelvic-fin rays 19–23); pectoral-fin origin below posterior margin of eye; pelvic fins not completely fused, posterior third not fused; mouth small, about half of head width, with horny jaw sheaths strongly curved towards vent; four pairs of very short barbels, two rostral and two maxillary; rostral cap fused with upper jaw except around base of rostral barbels; lower lip with medial groove well developed posterolaterally but interrupted anteromedially; snout rounded in dorsal view, strongly acuminate from lateral view; gill opening angular and large, above middle of pectoral-fin base to anterior of pectoral-fin origin; subopercular groove absent; base of first pectoral-fin ray separated from head by a deep groove parallel to anterior edge of fin ray on ventral side of head and continuous dorsally to gill opening, dorsal surface of pectoral-fin base without scales; supra-pelvic flap originating immediately behind pectoral-fin base and continuing as a free flap above anterior third of pelvic-fin base; abdomen without scales except for area where the pelvic fins are not fused; pored lateral scale rows 50–75; very short anal-fin base (3.6–6.6% SL); first anal-fin pterygiophore bifurcated; total vertebral count 27–28. Mature male with densely packed tubercles on anterior 5–6 pectoral-fin rays, and many tubercle ridges on opercle submargin. For Engkaria , the opercular tubercles appear as ridges of tubercles along the opercle submargin ( Fig. 19 ), and some ridges form a continuous line of up to 30 tubercles, a character unique to this genus. Engkaria eubranchus can be differentiated from other Bornean gastromyzontines in having the unique combination of characters: small mouth width (around ⅓ to ¼ of head width), shared with Hypergastromyzon and Parhomaloptera ; other genera Gastromyzon , Glaniopsis , Katibasia , Neogastromyzon , and Protomyzon having a wider mouth (½ to ¾ head width). Incomplete fusion of pelvic fins with posterior portion free, vs. complete fusion in Gastromyzon , Hypergastromyzon , and Neogastromyzon ; separate pelvic fins in Glaniopsis , Katibasia , Parhomaloptera , and Protomyzon . Greatly enlarged pectoral and pelvic fins which overlap to form a suction structure with the belly, shared with Gastromyzon , Hypergastromyzon , and Neogastromyzon . Engkaria can be differentiated from Hypergastromyzon by the following characters: large angular opercular opening with anterior edge at pectoral-fin origin, vs. small lunate opening above pectoral-fin ray 6–7; fewer vertebrae (27–28, vs. 30–32); longer rostral barbels than maxillary barbels (vs. short rostral barbels and more elongate maxillary barbels); more pectoral-fin rays (19–23, vs. 17–19); more transverse scales (10.1.10–11, vs. 7–9.1.7–9); less vertebrae (27–28, vs. 30–32); more thickset body (body depth at anus 11.2–13.1% SL, vs. 8.4–10.6; caudal-peduncle depth 7.8–8.5% SL, vs. 5.2–8.0); smaller pectoral-fin length (33.4–38.3% SL, vs. 36.7–42.5); smaller eye (2.9–4.4% SL, vs. 3.4–5.9).

This genus is restricted to western Borneo, currently known only from the upstream area (Engkari branch) of Lupar River basin in Central Sarawak. It inhabits fast-flowing hill streams with well-oxygenated water running over rock and gravel base. As currently recognised, the genus is monotypic.

Etymology. Named for the Engkari River (Lupar River basin), a riparian stream system within the Lanjak Entimau Wildlife Sanctuary, which drains into the Batang Ai reservoir; and currently known only from Engkari River. Latinised and gender feminine.

Type species. Hypergastromyzon eubranchus Roberts, 1991 .

Figures

Fig. 19. Engkaria eubranchus, ZRC 46068, 39.0 mm SL, male. Top: lateral view of head region showing tuberculation pattern on opercle; bottom: close-up of dorsal view of left pectoral fin showing tuberculation pattern (not to scale).