Kapuasia, Kottelat & Hui, 2024

Kottelat, Maurice & Hui, Tan Heok, 2024, Kapuasia, a genus name for ‘ Nemacheilus’ maculiceps (Teleostei: Nemacheilidae), Raffles Bulletin of Zoology 72, pp. 105-109 : 105-108

Kapuasia , new genus

Type species. Nemacheilus maculiceps Roberts, 1989 .

Etymology. Name derived from the Kapuas River in West Kalimantan, where the type species was first collected. Gender feminine.

Diagnosis. Kapuasia is distinguished from all other genera of Nemacheilidae in the morphology of the mouth. The mouth is strongly arched, U-shaped ( Fig. 4a ). The upper lip is swollen and smooth, the posterior edge is entire, without median incision, with a deep groove between the lip and the rostral cap. The edge of the rostral cap between the anterior rostral barbels is slightly crenulated. The processus dentiformis is present. The lower lip is swollen, with a deep groove (postlabial) along the lateral parts; its anterior edge is continuous, with a narrow shallow median longitudinal groove (mental) extending from the mental area to the anterior edge of the lip. The median part of the lower lip has 8–10 ridges on each side of the mental groove ( Fig. 4b ), radiating from the anterior extremity of the postlabial groove, across the whole lip, resulting in a crenulated inner edge of the lip; in some specimens, there is a longitudinal row of black pigments along most ridges.

Kapuasia is also distinguished from all nemacheilid loaches known to us by the presence of a conspicuous suprapectoral flap above the pectoral fin ( Fig. 5 ). Additional characters useful to distinguish the genus (but none unique to it) are: a well-developed pelvic axillary lobe, extending along the complete base of the fin; a small ridge along both dorsal and ventral midlines on the posterior part of the caudal peduncle; the anus about midway between the base of the pelvic fin and the origin of the anal fin; the pelvic fin with 1 unbranched and 7 branched rays; the pectoral fin with 1 unbranched and 9 or 10 branched rays [Roberts, 1990: 108 reported 10–12 branched rays]; the anal fin with 3 unbranched and 5½ branched rays; the dorsal fin with 4 unbranched and 8½ branched rays, its distal margin straight to slightly concave; the caudal fin deeply forked, the tip of the lobes slightly rounded, with 9+8 branched rays; the body entirely covered by scales, including on the predorsal area and the throat; the scales are very small, embedded; the lateral line is complete, with the pored scales difficult to count, estimated around 120–130; the cephalic lateral line canals have 5 (or 3?) supratemporal, 6 supraorbital, 11+3 infraorbital, and 8–10 preoperculo-mandibular pores; the anterior nostril is on the anterior side of a flap-like tube; there are no enlarged scales along the caudal peduncle; the eye protrudes slightly above the dorsal profile of the head; and the interorbital area is concave.

There is no black spot at the base of the anterior dorsal-fin rays or on their lower part, no ocellus at the upper extremity of the base of the caudal fin. There is a large, roughly triangular, black mark at the base of each lobe of the caudal fin.

The examined specimens have features for which sexual dimorphism has been documented in various nemacheilid genera. The pectoral-fin rays are hard and rigid, not curled. The unbranched and the three anterior branched rays are thicker than the remaining rays. The first branched pectoral-fin ray is branched only once, the branches are thick and the space between them narrow. In the second and third branched rays, the anterior branch is unbranched and thicker than the posterior one, with a membrane between the two branches; the posterior branch is branched and these sub-branches are adjacent, without or with only very narrow membrane in between. In the remaining branched rays, both branches are branched and there are membranes between the sub-branches. In the 64.3 mm SL specimen, there is a short row of short, small tubercles on the dorsal side of each branch of the first branched ray ( Fig. 6 ) and much less developed tubercles on the second branched ray. There are no tubercles in the other specimens. No suborbital flap is present.

Remarks. In a number of nemacheilid genera, the presence of tubercles on the dorsal side of the anterior pectoral-fin rays of the males, the pattern of their distribution, their size etc. are diagnostic features (e.g., see Kottelat, 2018, 2019; Conway & Kottelat, 2023). However, in males of some species their presence and development apparently vary with age, season, and sexual activity (MK, pers. obs.). Therefore, at this stage, we do not want to use the presence and shape of tubercles in a single specimen of Kapuasia as a character usable to diagnose the genus. Also, sex has not been confirmed by dissection. In all nemacheilid genera in which the morphology of the pectoral fin has been observed or reported with enough details, in the female, all branched rays are similarly slender and the branches of branched rays are all separated by membranes. This was not observed in the examined specimens.

Material examined. Kapuasia maculiceps : All from Indonesia: Borneo: Kalimantan Barat: Kapuas drainage: ZRC 56404 , 1 , 69.7 mm SL; Bengkayang area (0°49′N 109°29′E); aquarium-fish trade. — ZRC 61464 , 2 , 56.2 – 64.3 mm SL; Kec. Banyuke, Ulu Landak , Lokasi Desa Kampet , Kampet River (flowing into Mempawah R.), near Mt. Marabukatan. — ZRC 65285 , 1 , 86.6 mm SL; Putussibau. — MZB 3543 , holotype, 78.9 mm SL (photograph only); BMNH 1982.3 .29.135, 1 paratype, 72.0 mm SL (photograph only); RMNH 28878 , 1 , 79.0 mm SL (photograph only); rocky channel in mainstream of Sungai Pinoh, 37 km south of Nangapinoh , 0°39.5′S 111°40′E; T. R. Roberts, 24 July 1976 .

Kottelat & Tan: Kapuasia , new genus

Figures

Fig. 4. Kapuasia maculiceps; a, ZRC 61464, 64.3 mm SL; mouth; b, ZRC 65285, 86.6 mm SL; close up of anterior part of lower lip. Arrow: mental groove.

Fig. 5. Kapuasia maculiceps, ZRC 61464, 64.3 mm SL; head, pectoral fin and suprapectoral flap (arrow).

Fig. 6.Kapuasia maculiceps, ZRC 61464, 56.2. mm SL; pectoral fin, dorsal view; note tubercles near tip of first and second branched rays.