Kryptopterus platypogon, Heok Hee Ng, 2004

Heok Hee Ng, 2004, Kryptopterus platypogon, a new silurid catfish (Teleostei: Siluridae) from Borneo., Zootaxa 398, pp. 1-8 : 2-6

Kryptopterus platypogon sp. nov. (Figs. 1 & 2a)

Type material. Holotype: ZRC 45838 , male, 176.3 mm SL; Borneo : Sarawak, Rajang River drainage, market at Sibu , 2º17'18.6"N 111º49'49.2"E; H. H. Tan & Y. Y. Goh, 3-4 March 1998.

Diagnosis. Kryptopterus platypogon , K. hexapterus and K. cheveyi can be distinguished from congeners by a combination of the absence of a dorsal fin, a strongly-arched dorsal profile with a distinct nuchal concavity and vomerine teeth in a single ovoid patch. The key distinguishing characters among the three species are discussed below and in Table 1.

Kryptopterus platypogon differs from K. hexapterus in having a more strongly-projecting lower jaw (Fig. 2), larger eye (14.1% HL vs. 8.0-12.6), longer maxillary (135.6% HL vs. 40.0-120.4) and mandibular (119.3% HL vs. 32.3-80.0) barbels that are flattened and ribbon-like (vs. flattened, but ovoid in cross section), and more ventrally-placed eyes (about one quarter of the orbital margin visible when the head is viewed ventrally vs. orbital margin barely visible; Fig. 3). It is further distinguished from K. cheveyi in having a strongly projecting lower jaw (vs. upper and lower jaws of equal length), more anal-fin rays (83 vs. 66-71), narrower head (8.6% SL vs. 9.7-12.3) and smaller eye (14.1% HL vs. 18.9-22.7).

Description. Morphometric data in Table 2. Body laterally compressed; maximum body depth located at pelvic-fin origin; head as broad as body and moderately depressed. Dorsal profile of body strongly arched, with a pronounced nuchal concavity.

Snout rounded when viewed from above. Anterior pair of nostrils tubular and anteromedial to maxillary barbel base. Posterior pair of nostrils bordered by fleshy dorsal and ventral membranes and posteromedial to maxillary barbel base (at level of vertical through anterior orbital margin). Lower jaw strongly projecting forwards.

Mouth terminal; gape oblique, moderate and extending two-thirds of way between maxillary barbel base and anterior orbital margin. Well-developed rictal lobes present, subtended by deep submandibular groove; upper rictal lobe possessing skin fold with free dorsal edge extending from mouth corner to base of maxillary barbel. Thin, broad supralabial fold extending from below orbit to point two thirds of way between maxillary barbel base and anterior orbital margin.

Jaw teeth depressible and villiform. Premaxillary teeth in 4-5 irregular rows in narrow, gently curved rectangular bands. Dentary teeth in similar, slightly narrower bands narrowing posterolaterally, reaching from symphysis almost to mouth corners. First row of dentary teeth slightly visible when mouth is closed. Vomerine teeth in 2-3 rows in single ovoid patch straddling midline.

Two pairs of barbels, flattened and ribbon-like for entire length. Maxillary barbels reaching to middle of pectoral fin. Mandibular barbels (only outer pair present) reaching to middle of pectoral fin. Eyes small, subcutaneous (without free orbital margin); located at approximately anterior third of head and immediately behind supralabial fold. Dorsal orbital margin just visible dorsally; ventral quarter of orbital margin visible ventrally.

Gill membranes separate and overlapping, free from isthmus; gular fold well-developed and v-shaped. Branchiostegal rays 14. Gill rakers long and thin, without odontodes; anteriormost rakers on lower first arch widely spaced; 6+21.

Dorsal fin absent. Depressed pectoral fin reaching beyond origin of anal fin; distal margin broadly convex, with rounded tip. Fourth branched pectoral ray longest and fin with 13 rays. Proximal two-thirds of first pectoral-fin element co-ossified into a slender spine. Spine with shallow oblique striae on dorsal and ventral surfaces and with 5 serrations on posterior edge spanning the distal end of the ossified and proximal end of the flexible distal tip. Axillary pore small, located just above pectoral spine base. Depressed pelvic fin reaching to second or third anal-fin ray; distal margin convex with i,7 rays. Distal margin of anal fin straight, with 83 rays; separate from caudal fin. Integument over anal fin thickened proximally for two thirds of ray lengths; fin-ray erector muscles attaching to base of fin rays, ventralmost extent of muscles defined by area of thickened integument. Caudal peduncle slender. Caudal fin deeply forked, lobes elongate and with rounded tips; upper lobe slightly longer; principal rays i,7,8,i. Lateral line complete, extending to middle of caudal-fin base, with short branches along flanks directed posteroventrally. Urogenital papilla located immediately posterior to insertion of pelvic fin. Vertebrae 11+50=61.

Coloration. In 70% ethanol: Body and head pinkish cream and diffusely pigmented. Light powdering of melanophores on dorsal surface of head and on flanks above lateral line. Thin, diffuse band of melanophores along dorsal midline. Ventral surfaces immaculate and lacking pigmentation. All fins hyaline. Barbels unpigmented.

Distribution. Known from the Rajang River drainage in northern Borneo (Fig. 4).

Etymology. From the Greek platys, meaning flat, and pogon, meaning beard; in reference to the flat ribbon-like barbels of this species. Used as a noun.

Discussion

Bornbusch (1995) diagnosed the K. hexapterus species group as possessing the following synapomorphies: premaxilla with a slender toothless process extending posteriorly from the lateral corner of the premaxilla and nearly reaching the anterior margin of the metapterygoid, scaphium lacking an ascending process, and the first vertebral centrum lacking a pair of ventral crests. The group includes the following nominal species: K. hexapterus (Bleeker , 1851), K. cheveyi (Durand , 1940) and K. moorei Smith , 1945, with K. moorei considered a junior synonym of K. cheveyi (see Kottelat, 1998).

Superficially, members of the K. hexapterus group are easily distinguished from congeners in having a combination of the absence of a dorsal fin, a strongly-arched dorsal profile with a distinct nuchal concavity and vomerine teeth in a single ovoid patch. Kryptopterus schilbeides is the only other congener lacking a dorsal fin and with a strongly arched dorsal profile and distinct nuchal concavity, but it can be distinguished from the members of the K. hexapterus group in having the vomerine teeth in two elliptical patches (vs. in a single ovoid patch).

It is possible that the differences observed between K. hexapterus and K. platypogon are due to sexual dimorphism, but examination of the series of K. hexapterus collected together with the sole specimen of K. platypogon shows that this is not the case. Both males (easily distinguished by their strongly serrated pectoral spines) and females of K. hexapterus occur in the series, and sexual dimorphism in barbel, snout and eye morphology was not evident in this species. These differences are also not due to allometry, as a bivariate scatterplot of eye diameter and maxillary barbel length against SL (Fig. 5) indicates (it was not possible to plot mandibular barbel length against SL due to the fact that the mandibular barbels were broken off in many of the specimens).