Pseudomystus moeschii (Boulenger, 1890)

Heok Hee Ng & Kelvin K. P. Lim, 2005, The identity of Pseudomystus moeschii (Boulenger, 1890), with the description of two new species of bagrid catfishes from Southeast Asia (Teleostei: Bagridae)., Zootaxa 851, pp. 1-18 : 2-7

Pseudomystus moeschii (Boulenger, 1890)

Fig. 1

Liocassis moeschii Boulenger, 1890 : 39 (type locality: Deli River, Sumatra); Volz, 1907: 167.

Leiocassis moeschi - Weber & de Beaufort, 1913: 364.

Leiocassis moeschii - Kottelat et al., 1993: 64, pl. 31.

Material examined. BMNH 1889.11.12.66, lectotype, female, 71.0 mm SL; Sumatra: Deli. UMMZ 243700 (1), male, 66.9 mm SL; Sumatra: Sumatera Selatan, Sungai Merdak in the vicinity of Sukajaya, 1°55'54.1"N 103°44'23.7"E.

Diagnosis. Pseudomystus moeschii can be distinguished from congeners, except for P. carnosus and P. fumosus , in having an enlarged and prominent process of the post-temporal(the supraclavicular process of previous authors), which is almost as long as (vs. less than one third the length of) the postcleithral process, the presence (vs. absence) of long hair-like epithelial projections on the skin and long tubular extensions of the sensory pores. Pseudomystus moeschii can be distinguished from P. carnosus and P. fumosus in having a more slender body (13.0-14.5% SL vs. 14.9-16.7) and possessing (vs. lacking) lighter colored patches on the body. It further differs from P. carnosus in having a rounded (vs. pointed) tip of the nuchal shield (Fig. 2), and from P. fumosus in having less developed procurrent caudal rays that are evenly sloping along the anterior edges (vs. well developed procurrent caudal rays that curve sinuously along the edges; Fig. 3).

Description. Biometric data as in Table 1. Head depressed; dorsal profile slightly convex and ventral profile almost straight; snout broadly rounded when viewed dorsally. Bony elements of dorsal surface of head covered with thin skin; bones visible, especially on posterior half of neurocranium, and ornamented with numerous fine, radial grooves. Midline of cranium with fontanelle extending from behind snout to just beyond level of posterior orbital margin. Supraoccipital process moderately broad, with gently converging sides and blunt tip; extending to nuchal plate. Supratemporal with long posterior process, almost as long as cleithral process. Eye ovoid, horizontal axis longest, with free margin; located entirely in dorsal half of head. Gill openings wide, extending from post-temporal to beyond isthmus. Gill membranes free from isthmus, with 7 (2) branchiostegal rays. First branchial arch with 3+9 (1) gill rakers.

Mouth subterminal. Oral teeth small and viliform, in irregular rows on all tooth-bearing surfaces. Premaxillary tooth band rounded, of equal width throughout. Dentary tooth band much narrower than premaxillary tooth band at symphysis, tapering laterally. Vomerine tooth band unpaired, continuous across midline; smoothly arched along anterior margin, tapering laterally to point extending posteriorly past level of premaxillary band; band width narrower than premaxillary band at midline, widening laterally and then tapering to a sharp point postero-laterally.

Barbels in four pairs. Maxillary barbel slender, extending for three quarters of head length. Nasal barbel slender, extending to one third of distance between posterior orbital margin and dorsal-most extent of gill opening. Inner mandibular-barbel origin close to midline, thicker and longer than nasal barbel and extending for half of head length. Outer mandibular barbel originates postero-lateral of inner mandibular barbel, extending for three quarters of head length.

Body slightly compressed, becoming more so toward caudal peduncle. Dorsal profile rising evenly but not steeply from tip of snout to origin of dorsal fin and sloping gently ventrally from origin of dorsal fin to end of caudal peduncle. Ventral profile slightly convex to anal-fin base, then sloping slightly dorsally to end of caudal peduncle. Skin smooth, with long hair-like epithelial projections; projections especially prominent on head and dorsal third of body. Lateral line complete and mid-lateral in position, sensory pores of lateral line with long, tubular extensions. Vertebrae 17+24=41 (1).

Dorsal fin with spinelet, spine, and 7 (2) rays. Origin of dorsal fin anterior to midbody, about two-fifths of body. Dorsal fin margin convex, usually with anterior branch of fin rays longer than other branches. Dorsal fin spine short, straight and slender, posterior edge without serrations. Nuchal shield moderately broad, with rounded tip anteriorly.

Pectoral fin with stout spine, sharply pointed at tip, and 8 (2) rays. Anterior spine margin smooth; posterior spine margin with 13 large serrations along entire length (serrations fewer in smaller specimens). Pectoral fin margin straight anteriorly, convex posteriorly. Cleithral process moderately broad, with slightly convex dorsal margin and extending for two thirds of pectoral-spine length.

Pelvic fin origin at vertical through posterior end of dorsal-fin base, with i,5 (2) rays and slightly convex margin; tip of adpressed fin not reaching anal fin origin. Anus and urogenital openings located at vertical through middle of adpressed pelvic fin. Males with a conical genital papilla reaching to base of first anal-fin ray.

Adipose fin with convex margin for entire length, with deeply-incised posterior portion and origin in contact with base of last dorsal-fin ray; fin-base long, spanning twothirds of post-dorsal distance. Anal fin base just posterior to vertical through origin of adipose fin, with v,10 (2) rays and curved posterior margin.

Caudal peduncle moderately deep. Caudal fin deeply forked, with i,7,8,i (2) principal rays; upper lobe slender and lanceolate, lower lobe pointed. Procurrent rays extend anterior to fin base, with evenly-sloping anterior margins.

Coloration. In 70% ethanol: dorsal and lateral surfaces of head and body dark purplish brown, fading to brown on ventral surfaces of head and body. Lateral line with thin, pale stripe. Lateral surfaces of body with pairs of irregular brown patches located dorsal and ventral to lateral line: one at region between dorsal and adipose fins, another at middle of adipose fin base. Fifth pale spot at base of first few anal-fin rays. Adipose fin dark purplish gray. Dorsal, caudal and all paired fins with purplish gray fin rays and hyaline distal margin, inter-radial membranes of all fins with scattered melanophores. Barbels purplish gray dorsally, light gray ventrally.

Distribution. Known from eastern Sumatra (in the Deli and the Banjuasin River drainages; Fig. 4).