Silurichthys ligneolus, Ng, Heok Hee & Tan, Heok Hui, 2011

Ng, Heok Hee & Tan, Heok Hui, 2011, Silurichthys ligneolus, a new catfish (Teleostei: Siluridae) from southern Borneo, Indonesia, Zootaxa 2793, pp. 56-62 : 57-59

Silurichthys ligneolus sp. nov.

( Fig. 1 )

Type material. Holotype: MZB 17184, 55.3 mm SL; Indonesia, Borneo: Kalimantan Tengah, Kahayan River drainage, Rungan River sub-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; M. Kottelat & H. H. Tan, 5 March 2008.

Paratypes: CMK 21943 (1), 27.5 mm SL; ZRC 52048 (2), 25.0–43.0 mm SL; Indonesia, Borneo: Kalimantan Tengah, Sebangau River drainage, Sebangau River, blackwater canal draining from forest, 2°17'56.7"S 113°52'22.4"E; M. Kottelat & H. H. Tan, 6 March 2008.

Diagnosis. Silurichthys ligneolus can be distinguished from all congeners except for S. sanguineus in having 3–4 (vs. 5–7) principal rays on the lower caudal-fin lobe. It differs from S. sanguineus in having (vs. lacking) pelvic fins, fewer anal-fin rays (44–45 vs. 60) and vertebrae (46–48 vs. 57). The following combination of characters additionally distinguishes it from congeners: body depth at anus 9.1–11.0% SL, caudal peduncle depth 4.7–5.5% SL, eye diameter 6.7–9.8% HL, lower lobe of caudal fin indistinct, one gill raker on first branchial arch, and uniformly brown body.

Description. Biometric data are given in Table 1 . Body laterally compressed. Head somewhat depressed. Dorsal profile straight, descending gradually from dorsal-fin origin to snout tip. Anterior profile of snout rounded. Anterior pair of nostrils tubular and anteromedial to maxillary-barbel base. Posterior pair of nostrils bordered by fleshy dorsal and ventral membranes, situated posteromedial to maxillary-barbel base. Eyes small, subcutaneous; located in anterior half of head; visible dorsally, not visible ventrally.

Mouth subterminal; gape horizontal or very slightly oblique. Well-developed rictal fold present, consisting of large and fleshy upper lobe joined at corner of mouth with lower lobe; lower lobe subtended by short submandibular groove.

Teeth villiform. Dentary teeth in slightly curved, elongate bands narrowing posteriorly, reaching from symphysis almost to mouth corners; premaxillary teeth in broader, slightly curved rectangular bands; vomerine teeth in a single crescent-shaped band.

Maxillary barbels slightly flattened, reaching to anterior third of anal fin. One pair of mandibular barbels present; located slightly anterolateral to gular fold; barbels flattened for most of proximal length, reaching to middle of pectoral-fin base.

Gill membranes separate, overlapping, free from isthmus. Branchiostegal rays 9 (4). Gill rakers short, small; 0+1* (2).

Distal margin of dorsal fin pointed, with i,2 (4) rays; segments of first ray not co-ossified to form spine. Distal margin of pectoral fin broadly convex, with 7,i (2) or 8* (2) rays. Segments of the proximal two-thirds of first pectoral-fin element co-ossified, forming spine. Pectoral spine and articulated segments sexually dimorphic in mature individuals. Spine in males broad, somewhat flattened dorsoventrally, with 5–7 serrations on posterior edge, increasing in size distally; proximal articulated segments with 0–4 serrations on posterior edge. Spine in females and juveniles slender, without serrations on posterior edge of spine proper and proximal articulated segments. Distal margin of pelvic fin convex, with i,5,i (4) rays. Distal margin of anal fin straight, with 44 (2) or 45* (2) rays; joined to caudal fin for length of last anal-fin ray. Integument over anal fin thickened proximally for slightly more than half of ray lengths; fin-ray erector muscles extending along anterior edges of anal-fin rays, ventralmost extent of muscles that of thickened integument. Caudal fin very obliquely truncate, lower lobe not markedly distinct from upper lobe; principal rays i,6,3* (3) or i,6,3,i (1).

Vertebrae 11+35=46* (1), 11+36=47 (1) or 11+37=48 (2).

Coloration. In 70% ethanol: flanks and thickened integument over anal fin chestnut brown. Dorsal surface and sides of head uniformly chestnut brown, fading to dark yellow on ventral surfaces of head, breast and belly. Maxillary and mandibular barbels brown, fading to yellow distally. Dorsal, pectoral, pelvic and anal fins hyaline; anal fin with scattering of melanophores along fin rays imparting very diffuse brown color. Caudal fin largely hyaline, with scattered melanophores imparting diffuse brownish color at its base.

Distribution. This species is known only from blackwater habitats in the Kahayan and Sebangau river drainages in southern Borneo ( Fig. 2 ).

Etymology. The specific epithet comes from the Latin ligneolus , the diminutive form of the Latin noun ligneus, meaning wood. This name is used in allusion to the slender, uniformly brown body of this species (resembling a small piece of wood).

Figures

FIGURE 1. Silurichthys ligneolus, holotype, MZB 17184, 55.3 mm SL; Borneo: Kahayan River drainage.

FIGURE 2. Map showing collecting localities of Silurichthys ligneolus.

Tables

TABLE 1. Morphometric data for Silurichthys ligneolus (n = 4).

	Holotype	Range	Mean±SD
% SL
Predorsal length	26.8	26.8–28.7	27.7±0.87
Preanal length	30.6	30.6–34.8	32.8±1.73
Prepelvic length	26.9	26.9–30.2	28.6±1.74
Prepectoral length	16.6	16.6–20.4	18.9±1.64
Length of dorsal-fin base	1.8	1.5–1.8	1.7±0.13
Anal-fin length	68.7	64.7–68.7	66.9±1.65
Pelvic-fin length	7.5	6.8–7.5	7.1±0.33
Pectoral-fin length	14.5	13.8–15.1	14.5±0.53
Pectoral-spine length	8.1	6.0–8.1	7.4±0.97
Caudal-fin length	30.9	25.1–30.9	28.2±2.56
Body depth at anus	11.0	9.1–11.0	10.2±0.88
Caudal peduncle depth	4.7	4.7–5.5	4.9±0.39
Head length	16.3	16.3–21.8	19.2±2.44
Head width	12.8	11.0–13.2	12.4±0.97
Head depth	9.4	8.2–11.2	9.7±1.24
% HL
Snout length	34.4	33.3–37.3	34.9±1.71
Interorbital distance	37.8	36.9–40.0	38.5±1.39
Eye diameter	6.7	6.7–9.8	8.0±1.39
Maxillary barbel length	243.3	146.7–243.3	201.3±54.21
Mandibular barbel length	111.1	102.0–118.3	112.0±7.36