Clarias insolitus , Heok Hee Ng, 2003
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Type material. Holotype: MZB 6112, 122.5 mm SL; Borneo : Kalimantan Tengah, Barito River drainage ; small stream flowing into Sungai Rekut (tributary of Sungai Busang) about 1.5 km upstream from the Project Barito Ulu base camp on Sungai Busang ; D. Siebert, O. Crimmen & A. Tjakrawidjaja, 5 February 1991.
Paratypes: BMNH 2001.1.15.98-103, 7 ex., 53.5-139.7 mm SL; data as for holotype.
Diagnosis. Clarias insolitus ZBK differs from other Southeast Asian Clarias ZBK [[in having]] hypertrophied sensory canal pores on the head and body easily visible to the naked eye (vs. sensory canal pores indistinct and not visible without magnification) and (except for C.batrachus ) in having a long and thin (“knife-shaped” of Teugels, 1986) anterior fontanel [all other Asian species have a short and squat (“sole-shaped” of Teugels, 1986) anterior fontanel]. Clarias insolitus ZBK can be further distinguished from all other Southeast Asian Clarias ZBK (except for C. intermedius ZBK , C, meladerma ZBK , C. olivaceus , and C. planiceps ZBK ) in having prominent serrations on the anterior edge of the pectoral spine (vs. anterior edge smooth or with low, indistinct asperities forming a rugose edge) and (except for C. olivaceus and C. planiceps ZBK ) in lacking white spots on the body. Clarias insolitus ZBK further differs from C. intermedius ZBK and C. meladerma ZBK in having a longer distance between the tip of the occipital process and the base of the first dorsal-fin ray (10.3-12.4% SL vs. 3.1-5.6) and a more slender body (9.9-11.5% SL vs. 13.7-16.6), from C. olivaceus in having a more slender body (9.9-11.5% SL vs. 12.5-15.2) and narrower head (14.0-15.6% SL vs. 16.0-18.7 and from C. planiceps ZBK in having a longer snout (32.5-37.7% HL vs. 20.6-28.7) and smaller interorbital distance (39.4-43.6% HL vs. 46.4-49.9).
Description. Head depressed; dorsal profile slightly convex and ventral profile almost straight. Bony elements of dorsal surface of head covered with thick skin; bones not readily visible, but sutures sometimes evident. Anterior fontanel long and thin (“knifeshaped ” of Teugels, 1986); anterior tip reaching just beyond line through anterior orbital margins. Occipital process acutely rounded. Eye ovoid, horizontal axis longest, subcutaneous; located dorsolaterally on head. Gill openings narrow, extending from dorsal-most point of pectoral-fin base to isthmus. Gill membranes free from isthmus but united to each other with 7 (n=6) or 8 (n=2) branchiostegal rays. First branchial arch with 2+10 (n=2) or 2+12 (n=6) gill rakers.
Mouth subterminal, with fleshy, plicate lips. Oral teeth small and in irregular rows on all tooth-bearing surfaces. Premaxillary tooth band rectangular, with median notch on posterior edge. Dentary tooth band much narrower than premaxillary tooth band at symphysis, tapering laterally. Vomerine tooth band unpaired, continuous across midline, crescentic and smoothly arched along anterior margin, posterior margin with a median process. Premaxillary and dentary teeth viliform; vomerine teeth subgranular.
Barbels in four pairs; long and slender with thick fleshy bases. Maxillary barbel extending nearly to base of first dorsal-fin ray. Nasal barbel, extending nearly to tip of occipital process. Inner mandibular-barbel origin close to midline; barbel thicker and longer than nasal barbel and extending to base of pectoral spine. Outer mandibular barbel originates posterolateral of inner mandibular barbel, extending to tip of pectoral fin. Body cylindrical, becoming compressed towards caudal peduncle. Dorsal profile rising very gently from tip of snout to origin of dorsal fin and thereafter almost horizontal to end of caudal peduncle. Ventral profile slightly convex to middle of head and thereafter almost horizontal to end of caudal peduncle.
Skin smooth. Lateral line complete and midlateral in position. Vertebrae 19+42=61 (n=1), 18+44=62 (n=1), 20+42=62 (n=3), 21+41=62 (n=1), or 20+43=63 (n=2).
Dorsal fin with long base, spanning posterior three-quarters of body; with 67 (n=2), 68 (n=1), 71 (n=2), 72 (n=1), 75 (n=1) or 76 (n=1) rays covered by thick layer of skin and without spine. Dorsal-fin margin straight, parallel to dorsal edge of body.
Pectoral fin with small spine, sharply pointed at tip, and 8 (n=8) rays. Proximal threequarters of anterior spine margin with large serrations; distal quarter of anterior spine margin and posterior spine margin smooth. Pectoral-fin margin straight anteriorly, convex posteriorly.
Pelvic-fin origin at anterior third of body, with i,5 (n=8) rays and convex margin; tip of adpressed fin reaching base of first few anal-fin rays. Anus and urogenital openings located at vertical through middle of adpressed pelvic fin.
Anal fin with long base and 53 (n=1), 55 (n=2), 56 (n=2), 58 (n=2) or 63 (n=1) rays covered by thick layer of skin; margin straight and parallel to ventral edge of body. Caudal peduncle very short. Caudal fin rounded, with i,6,6,i (n=8) principal rays.
Morphometric data as in Table 1.
Color. Dorsal and lateral surfaces of head and body violet-gray, fading to pale gray on ventral surfaces. Dorsal, anal and caudal fins violet-gray with very thin hyaline distal margin. Pectoral-fin rays violet-gray, with hyaline interradial membranes. Pelvic fins hyaline. Barbels and pectoral spines violet-gray dorsally and light grey ventrally.
Distribution. Known from the upper Barito River drainage in southern Borneo (Fig. 3).
Etymology. From the Latin insolitus, meaning strange; in reference to the combination of hypertrophied sensory canal pores and a knife-shaped anterior fontanel, which is not seen in other Southeast Asian Clarias ZBK . Used as a noun in apposition.
Recent taxonomic studies on Southeast Asian Clarias ZBK have divided them into three species groups based on the distance between the tip of the occipital process and the base of the first dorsal ray and the relative length of the body as expressed by the number of dorsal- and anal-fin rays and vertebrae (Ng, 1999). Until a detailed phylogenetic study can be undertaken to ascertain if the species groups are indeed natural, this approach is not utilized here, largely because the characters that diagnose Clarias insolitus ZBK are highly distinctive and not seen in other Southeast Asian taxa.
The color pattern of C. insolitus ZBK is also distinct in lacking white spots on the body. A color pattern consisting either of a uniform color or one with small, indistinct white spots is shared with only two other species of Southeast Asian Clarias ZBK , viz. C. batu ZBK and C. planiceps ZBK . However, C. insolitus ZBK can be distinguished from C. planiceps ZBK by the characters mentioned in the diagnosis and from C. batu ZBK by the number of vertebrae (61-63 vs. 67- 71).
Among other Southeast Asian Clarias ZBK , a long and thin anterior fontanel is only found in C. batrachus (Teugels et al., 1999), which can be easily distinguished from C. insolitus ZBK in having a smaller distance between the tip of the supraoccipital and the base of the first dorsal-fin ray (5.8-8.2% SL vs. 10.3-12.4), as well as the characters already mentioned in the diagnosis, i.e. indistinct (vs. hypertrophied) sensory canal pores on the head and body, presence (vs. absence) of white spots on the body, and anterior edge of the pectoral spine smooth or with low asperities (vs. with prominent serrations).
United Kingdom, London, The Natural History Museum [formerly British Museum (Natural History)]
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