Chaca serica, a new species of frogmouth catfish (Teleostei: Siluriformes) from southern Borneo Author Ng, Heok Hee Author Kottelat, Maurice text Zootaxa 2012 3258 37 45 journal article 10.5281/zenodo.280697 fb03e531-451f-42b1-a9eb-cb615e4c07ae 1175-5326 280697 Chaca serica new species ( Figs. 2 , 3 a) Chaca bankanensis (non Bleeker) —Bleeker, 1855 : 165 ; 1858: 323 (in part); 1863: 96 (in part). Type material. Holotype : MZB 17202 , 137.6 mm SL ; Borneo: Kalimantan Tengah, Kahayan River drainage, Danau Tahai; H. H. Tan & M. Kottelat, 4 March 2008 . FIGURE 2. Chaca serica , MZB 17202, holotype, 137.6 mm SL; Borneo: Kalimantan Tengah, Danau Tahai. Paratypes : ZRC 53190 (1), 109.6 mm SL ; Borneo: Kalimantan Tengah, Kapuas River drainage, Bargugus, blackwater stream ca. 47 km after bridge over Kahayan River at Palangkaraya, 1°56'18.1"S 114°4'21.1"E ; H. H. Tan & M. Kottelat, 7 March 2008 . MZB 17202 (3), 77.7–133.2 mm SL ; ZRC 53192 (8), 76.5–145.3 mm SL ; CMK 20319 (12), 64.1–136.0 mm SL ; data as for holotype . ZRC 51240 (7), 94.5–143.2 mm SL ; Borneo: Kalimantan Tengah, Rungan River drainage; P. Yap, December 2003 . ZRC 53193 (2), 102.5–111.8 mm SL ; Borneo: Kalimantan Tengah, Tahai, junction of Sungai Tahai with Danau Tahai, 2°1'27.9"S 113°46'37.4"E ; H. H. Tan et al., 21 August 2009 . ZRC 53191 (1), 127.0 mm SL ; Borneo: Kalimantan Tengah, Kahayan River drainage, Sungai Tahai, flowing into Rungan River ca. 30 km outside Palangkaraya, 2°1'40.4"S 113°45'50.9"E ; H. H. Tan et al., 16 August 2009 . ZRC 53189 (2), 127.0– 131.8 mm SL ; CMK 20368 (1), 123.2 mm SL ; Borneo: Kalimantan Tengah, Kahayan River drainage, Rungan River at Nyaru Menteng; H. H. Tan & M. Kottelat, 5 March 2008 . ZRC 53188 (1), 77.0 mm SL ; CMK 20350 (1), 59.9 mm SL ; Borneo: Kalimantan Tengah, Kahayan River drainage, Sungai Panta, blackwater river draining into Rungan River and its confluence, connected to Nyaru Menteng, 2°2'1.0"S 113°47'5.5"E ; H. H. Tan & M. Kottelat, 5 March 2008 . CAS 96987 (2), 44.0– 50.4 mm SL ; Borneo: Kalimantan Tengah, Mentaya River drainage, Sungai Ramban, 22 km west of Sampit on road to Pembuanghulu; T. R. Roberts, 11 June 1992 . Non-type: BMNH 1863.12.4.117 (1), 108.5 mm SL ; Borneo: Kalimantan Selatan, Barito River drainage, Banjarmasin; C. Helfrich, ca. October 1854 ( Kottelat, 2011: 58 ). Diagnosis. Chaca serica is distinguished from C. bankanensis in lacking (vs. having) a series of rugose ridges on the oral margin of the lower lip ( Fig. 3 ), and generally longer dorsal and ventral procurrent caudal-ray bases (32.8–37.3% SL vs. 29.4–32.8 and 16.0–19.2% SL vs. 13.6–16.3 respectively), and from both C. burmensis and C. chaca in having (vs. lacking) nasal barbels, four (vs. five) pectoral-fin rays, and lacking (vs. having) a row of fimbriate skin flaps on the body dorsal to (and sometimes ventral to) the lateral line. It additionally differs from C. burmensis in having (vs. lacking) papillae around the eyes, a temporal fossa extending (vs. not extending) to the supraoccipital, and fewer serrae on the anterior edge of the pectoral spine (7–8 vs. 11–19). FIGURE 3. Dorsal view of heads of: a. Chaca serica , ZRC 53192, paratype, 145.3 mm SL; b. C. bankanensis , ZRC 53194, 151.2 mm SL, showing differences in the morphology of the oral margin of the lower lip. Description. Head and anterior half of body to region between pelvic- and anal-fin bases strongly depressed; body posterior to region between pelvic- and anal-fin bases compressed. Head appearing square in dorsal view, with snout truncate or slightly convex. Anterior naris located on anterior margin of snout; naris tubular and directed anteriorly. Posterior naris ovoid and subtended anterolaterally by small nasal barbel. Maxilla strongly developed and prominent as convex lobe at lateral margin of upper jaw. Dorsal surface of neurocranium covered with thick, tuberculate skin. Small, fimbriate skin flaps covering parts of dorsal and lateral surfaces of head, particularly in buccal region and along lateral margins. Supraoccipital process relatively short, contacting anterior nuchal plate element. Eye small and ovoid, horizontal axis longest; dorsally directed and located at about anterior third of head. Gill openings narrow, extending from posttemporal to just ventral to base of pectoral spine. Mouth superior; lower jaw slightly longer than upper. Oral margin of lower lip relatively smooth, lacking rugose ridges. Oral teeth small, villiform, in irregular rows on all tooth-bearing surfaces. Premaxillary and dentary tooth bands broad, curved, slightly narrower at symphysis and laterally. Palatal (vomerine) teeth absent. Gill arches without rakers. Branchiostegal rays 6 (15). Barbels short, in four pairs. Maxillary barbel short, slender, extending for distance approximately equal to width of maxilla. Nasal barbel much shorter than maxillary barbel and slender, extending for approximately onefifth of distance between orbit and posterior naris. Inner mandibular-barbel origin close to midline; barbel thicker and longer than nasal barbel, extending for approximately one-sixth distance between its base and base of pectoral spine. Outer mandibular barbel originating posterolateral of inner mandibular barbel, extending for approximately one-third of distance between its base and base of pectoral spine. TABLE 1. Biometric data for Chaca serica (n=15).

Standard length (mm) %SL	Holotype MZB 17202 137.6	Range 76.5–145.3	Mean±SD
Predorsal length Preanal length Prepelvic length	37.6 69.1 50.6	37.6–40.8 67.0–71.1 45.3–51.3	38.8±1.13 69.1±1.51 49.6±2.09
Prepectoral length Dorsal-fin base length	33.0 9.3	33.0–35.8 8.6–10.8	34.6±0.96 9.5±0.84
Dorsal-spine length Anal-fin base length Pelvic-fin length Pectoral-fin length	7.9 9.9 16.4 12.1	5.6–9.7 9.4–12.6 16.1–20.9 11.9–16.0	7.2±1.23 10.6±1.09 17.9±1.52 14.1±1.50
Pectoral spine length Caudal-fin length	10.6 17.6	9.1–13.4 16.4–20.9	11.4±1.62 18.5±1.71
Dorsal procurrent caudal-ray base length Ventral procurrent caudal-ray base length Dorsal to adipose distance Head length	34.1 17.2 6.9 37.1	32.8–37.3 16.0–19.2 5.9–8.6 37.1–41.2	34.7±1.35 17.1±0.88 7.2±0.80 39.0±1.21
Head width Head depth	29.7 14.5	29.7–35.7 14.2–18.6	31.9±1.99 16.0±1.57
%HL
Snout length Interorbital distance Eye diameter Nasal barbel length Maxillary barbel length	30.0 46.7 4.5 2.2 10.8	28.2–32.8 45.6–53.9 3.1–5.5 2.2–5.7 10.8–19.8	30.5±1.46 48.8±2.80 4.3±0.79 3.4±0.96 14.6±3.16
Inner mandibular barbel length Outer mandibular barbel length	15.5 22.0	12.8–18.2 9.8–22.0	15.5±2.02 17.2±3.43

Body depressed for anterior half and compressed for posterior half. Dorsal profile gently and almost evenly sloping from tip of snout to base of dorsal spine; sloping gently ventrally from origin of dorsal fin to end of caudal peduncle. Ventral profile of body almost horizontal to anal-fin base, then curving dorsally to end of caudal peduncle. Lateral line incomplete, extending to level of anal-fin origin. Vertebral column with 15+18=33* (1), 16+17=33 (1), 17+16=33 (1), 15+19=34 (1), 16+18=34 (11), 16+19=35 (4) or 17+18=35 (1) vertebrae and 4 ribs. Skin of dorsal and dorsolateral surfaces of head and body covered with numerous small tubercles, with larger conical papillae arranged loosely in longitudinal series along dorsal and dorsolateral surface of body in region between base of last dorsal-fin ray and first dorsal procurrent caudal-fin ray. Dorsal fin with spinelet, spine, and 4 (15) rays. Origin of dorsal fin at about two-fifths length of body. Distal margin of dorsal-fin convex, with all branches of fin rays of approximately equal length. First and second soft dorsal-fin rays longer than third and fourth rays. Dorsal-fin spine straight, short, stout, its anterior and posterior edges smooth. Anterior nuchal plate element narrow, elongate, pyriform. Pectoral fin with broad, somewhat depressed spine, sharply pointed at tip, and 4 (15) rays. Anterior margin of spine with 7–8 serrae; posterior margin of spine curved, smooth, with broad, flange-like expansion. First soft pectoral-fin ray longest, posterior rays becoming progressively shorter. Pectoral-fin margin straight anteriorly, convex posteriorly. Pelvic-fin origin posterior to vertical through posterior end of dorsal-fin base, with 6 (15) rays and broadly convex distal margin; tip of adpressed fin not reaching anal-fin origin. Anus and urogenital openings located at vertical through middle of adpressed pelvic fin. Adipose ridge short, spanning about one-sixth of SL. Ridge extending from immediately posterior to base of last dorsal-fin ray to first dorsal procurrent caudal-fin ray. Anal fin origin located approximately at middle of SL; anal-fin base short. Anal-fin margin straight anteriorly, convex posteriorly; with ii,4 (1), ii,4,i (1), ii,5,i (2), ii,6* (2), iii,3,ii (1), iii,4,i (1), iii,5 (3), iv,3,i (1), iv,4 (1) or iii,6 (2) fin rays. Last ray free from caudal peduncle. Caudal peduncle slender, narrowing posteriorly. Caudal fin rounded; fin with ii,4,5 (1), i,5,5* (8), 5,5,i (3), 6,4,i (1), 5,4,ii (1) or 5,6 (1) principal rays. Procurrent rays greatly enlarged and extending considerably anterior to fin base, extending for three-fifths of postdorsal distance dorsally and reaching almost to base of last anal-fin ray ventrally. Caudal fin with 22 (1), 23 (1), 24 (5), 25* (4), 26 (3) or 27 (1) dorsal procurrent rays and 11 (1), 12* (10), 13 (3) or 14 (1) ventral procurrent rays. FIGURE 4. Map showing distribution of species of Chaca in Southeast Asia. Solid symbols indicate records based on specimens examined, open symbols indicate records from the literature (Weber & de Beaufort, 1913; de Beaufort, 1939; Roberts, 1989). Each point may represent more than one locality. Coloration. In 70% ethanol and in life: Base color of head and body chestnut brown in most individuals examined; some individuals with dark-brown base color. Color becoming paler, less uniform and more blotchy towards ventrolateral and ventral surfaces of head and body, becoming a blotchy light brown ventrally. Individuals with chestnut-brown base color typically with large, ovoid, dark-brown blotches of varying size on dorsal and lateral surfaces of head and body. All fins chestnut or dark brown, with narrow hyaline margin, and hyaline regions frequently present at bases. Fin rays of pectoral, pelvic, anal and caudal fins frequently with mottled coloration. Dark-brown spots as on body sometimes present on dorsal fins of some individuals. Distribution. Chaca serica is known from the Barito, Kahayan, Kapuas (not to be confused with the larger river with an identical name in western Borneo) and the Mentaya river drainages in southern Borneo ( Fig. 4 ). Etymology. The specific epithet comes from the Latin adjective sericus meaning made of silk, or silken, in allusion to the smooth oral margin of the lower lip when compared to C. bankanensis , the congener that it superficially resembles most.