Glyptothorax exodon, Ng & Rachmatika, 2005

Ng, Heok Hee & Rachmatika, Ike, 2005, Glyptothorax Exodon, A New Species Of Rheophilic Catfish From Borneo (Teleostei: Sisoridae), Raffles Bulletin of Zoology 53 (2), pp. 251-255 : 251-253

Glyptothorax exodon , new species

( Fig. 1 )

Bagarius bagarius (non Hamilton) Vaillant, 1902: 72.

Glyptothorax platypogonoides (non Bleeker) Roberts, 1989: 136, Fig. 104.

Glyptothorax aff. platypogonoides Ng & Rachmatika, 1999: 182 , Fig. 8B.

Material examined. – Holotype - MZB 9940 , 57.5 mm SL, Borneo: Kalimantan Barat, Sungai Tekelan, coll. I. Rachmatika, 5 Sep.1997.

Paratypes – BMNH 19823.29 .190 (1), 63.2 mm SL ; CAS 49419 (1), 59.0 mm SL , RMNH 28907 (1), 57.2 mm SL, Borneo: Kalimantan Barat, mainstream of Sungai Pinoh , 20–60 km upstream from Nangapinoh, coll . T. R. Roberts & S. Wirjoatmodjo, 22–26 Jul.1976 ; RMNH 7845 (1), 60.2 mm SL, Borneo: Kalimantan Barat, Nanga Raun , coll. J. Büttikofer, 1897 ; MZB 9412 (2), 55.1–60.0 mm SL, Borneo: Kalimantan Barat, Embaloh, Sungai Jaket , coll. I. Rachmatika et al., 19 Sep.1997 .

Diagnosis. – Glyptothorax exodon be distinguished from Sundaic congeners except G. platypogonides and G. siamensis in having a slender body (13.8–15.8% SL vs. 17.3–20.9). It differs from G. platypogonides in having a deeper caudal peduncle (6.8–7.3% SL vs. 5.7–6.7) and more exposed premaxillary teeth when the mouth is closed ( Fig. 2 ) and from G. siamensis in having a larger eye (10.4–13.2% HL vs. 7.5– 9.1) and a mottled color pattern lacking distinct pale stripes (vs. a uniform dark brown with distinct pale midlateral and mid-dorsal stripes).

Description. – Morphometric data in Table 1. Head depressed, body moderately compressed. Dorsal profile rising evenly from tip of snout to origin of dorsal fin, then sloping gently ventrally from there to end of caudal peduncle. Ventral profile flat to anal-fin base, then sloping gently dorsally from there to end of caudal peduncle. Anus and urogenital openings located at vertical through middle of adpressed pelvic fin. Skin prominently tuberculate, with ovoid tubercles particularly visible on sides of body. Lateral line complete and midlateral. Vertebrae 17+18=35 (1), 17+19=36 (2), 18+18=36 (2) or 18+19=37 (2).

Head depressed and narrow, triangular when viewed laterally and with acute snout margin when viewed from above. Snout prominent. Anterior and posterior nares large and separated only by base of nasal barbel. Gill openings broad, extending from immediately ventral to posttemporal to isthmus. Bony elements of dorsal surface of head covered with thick, tuberculate skin. Eye ovoid, horizontal axis longest; located entirely in dorsal half of head. Orbit with free margin.

Barbels in four pairs. Maxillary barbel long and slender, extending to middle of pectoral-fin base. Nasal barbel slender, extending to midway between its base and anterior orbital margin. Inner mandibular-barbel origin close to midline, extending to two thirds of distance between its base and that of pectoral spine. Outer mandibular barbel originating posterolateral of inner mandibular barbel, extending to base of pectoral spine.

Mouth inferior, premaxillary tooth band almost wholly exposed when mouth is closed. Oral teeth small and villiform, in irregular rows on all tooth-bearing surfaces. Premaxillary teeth in single broad semilunate band. Dentary teeth in two narrow crescentic bands separated at midline.

Dorsal fin located above anterior third of body, with I,6 (7) rays; fin margin convex; spine short and gently curved. Adipose fin with anterior margin concave and posterior margin angular. Caudal fin strongly forked, with equal upper and lower lobes and i,7,8,i (7) principal rays. Procurrent rays symmetrical and extending only slightly anterior to fin base. Anal-fin base ventral to adipose-fin origin. Anal fin with straight anterior margin and straight or slightly concave posterior margin; with iv,8 (2) or iv,9 (5) rays. Pelvic-fin origin immediately posterior to vertical through posterior end of dorsal-fin base. Pelvic fin with slightly convex margin and i,5 (7) rays; tip of adpressed fin not reaching anal-fin origin. Pectoral fin with I,8 (7) rays; posterior fin margin slightly concave; anterior spine margin smooth, posterior margin with 10–12 serrations. Thoracic adhesive apparatus present, located on belly and consisting of logitudinal pleats of skin in narrow elliptical field. Adhesive apparatus with median depression on posterior half and extending from just behind gill opening to level of base of posteriormost pectoralfin ray.

Coloration. – In 70% ethanol: Dorsal and lateral surfaces of head, and body brown to brownish gray, fading to beige on ventral surfaces. A dark, diffuse midlateral stripe running along lateral line; lateral line without such pigmentation in some individuals, causing it to show up as paler stripe within darker stripe. Body with several long, elliptical pale spots: first above lateral line and spanning region between dorsal and adipose fins, second on anterior half of caudal peduncle above lateral line and third on anterior half of caudal peduncle below lateral line. Dorsal fin with brown base and broad subdistal triangular brown mark. Pectoral fins hyaline, with brown melanophores forming a diffuse broad, transverse band subdistally. Pelvic fin hyaline, with faint transverse brown band in middle. Anal fin with brown base and brown melanophores forming V-shaped subdistal mark on anterior half of fin; rest of fin hyaline. Adipose fin brown to brownish gray, with hyaline distal margin. Caudal fin brown to brownish gray, tips and posterior margins of lobes hyaline. Maxillary barbels brown to brownish gray dorsally, beige ventrally.

Distribution. – Known from the Kapuas River drainage in western Borneo ( Fig. 3).

Etymology. – From the Greek exo- (out) and odontos (tooth), in reference to the exposed premaxillary teeth.

Habitat. – Glyptothorax exodon is found in swift, clear streams with a substrate consisting of gravel, cobbles or large rocks ( Roberts, 1989). Other fish found in this habitat include Barbonymus collingwoodi , Crossocheilus spp., Cyclocheilichthys repasson , Epalzeorhynchos kalopterus , Garra borneensis , Paracrossocheilus spp., Puntius spp., Rasbora spp., Schismatorhynchos heterorhynchus , Tor tambroides , Gastromyzon contractus , Nemacheilus kapuasensis , Glyptothorax major , Hemibagrus cf. nemurus , Doryichthys martensii , Mastacembelus spp. and Auriglobus amabilis .

Figures

Fig. 1. Glyptothorax exodon, paratype, RMNH 28907, 57.2 mm SL; Borneo: Sungai Pinoh. Dorsal, lateral and ventral views.

Fig. 2. Ventral views of heads of: a. Glyptothorax exodon, RMNH 28907, paratype, 57.2 mm SL; b. G. platypogonides, ZRC 41588, 56.0 mm SL. Scale bar represents 5 mm.