Mystus falcarius, Prosanta Chakrabarty & Heok Hee Ng, 2005

Prosanta Chakrabarty & Heok Hee Ng, 2005, The identity of catfishes identified as Mystus cavasius (Hamilton, 1822) (Teleostei: Bagridae), with a description of a new species from Myanmar., Zootaxa 1093, pp. 1-24 : 13-17

Mystus falcarius sp. nov.

(Fig. 7)

Bagrus cavasius (non Hamilton, 1822) Blyth, 1858: 284; Blyth, 1860: 149.

Macrones cavasius (non Hamilton) Day, 1877: 447, Pl. C Fig. 1 (in part); Day, 1889: 155 (in part); Vinciguerra, 1890: 28 (in part); Jenkins, 1910: 137; Chaudhuri, 1911: 20; Kyaw Win, 1971: 52, Fig. 20 (5).

Aoria cavasius (non Hamilton) Prashad & Mukerji, 1929: 179; Mukerji, 1933: 815.

Mystus (Mystus) cavasius (non Hamilton) Jayaram, 1954: 532, Fig. 2 (in part); Misra, 1976: 87, Fig. 18 (in part).

Mystus cavasius (non Hamilton) Tint Hlaing, 1971: 513; Jayaram, 1981: 196, Fig. 92A (in part); Dutt et al., 1982: 27 (in part); Sharma & Dutt, 1983: 334 (in part); Talwar & Jhingran, 1991: 559, Fig. 184 (in part); Roberts, 1994: 248, Fig. 3 (in part); Jayaram, 1999: 235, Fig. 118C (in part); Menon, 1999: 200 (in part); Jayaram & Anuradha Sanyal, 2003: 46, Fig. 5 (in part).

Mystus near cavasius #1 Roberts, 1989: 124.

Type material. Holotype: CAS 89001, 170.2 mm SL; Myanmar: Kachin State, Myitkyina market; C.J. Ferraris, 21- 22 April 1996.

Paratypes: BMNH 1891.11.30.210-219 (13), 96.0-139.6 mm SL; Myanmar: Sittaung River and adjacent streams from Taungoo to about 240 km S; E.W. Oates, date unknown. CAS 79033 (2), 118.8-124.8 mm SL; Myanmar: Yangon market; T.R. Roberts, 5- 12 March 1985. CAS 89000 (4), 92.2-125.8 mm SL ; USNM 344668 (6), 74.8-99.0 mm SL; Myanmar: Sagaing Division, Pinda River in vicinity of Pinda Village, 23°10'59"N 94°5'37"E; C.J. Ferraris et al., 24 April 1996. CAS 92932 (1), 101.6 mm SL; Myanmar: Taninthayi Division, Tenasserim River backwater, midway between Htee-tah & Baowashung; T.R. Roberts, 12 March 1992. CAS 96569 (1), 190.4 mm SL; Myanmar: Taninthayi Division, Tenasserim River and tributaries midway between Htee-tah & Baowashung; T.R. Roberts, March 1992. USNM 343550 (1), 80.1 mm SL; Myanmar: Bago Division, Sittaung River at Taungoo; C.J. Ferraris & D. Catania, 7 April 1996.

Diagnosis. Mystus falcarius differs from other congeners with a long-based adipose fin (except M. cavasius and M. seengtee ) in having a combination of a black spot in front of the dorsal-spine base, a dark humeral mark, a body without distinct midlateral stripes, very long maxillary barbels reaching to caudal-fin base, dorsal spine short and feebly serrate, tall dorsal fin, and 22-29 rakers on the first gill arch. It can be distinguished from M. cavasius and M. seengtee in having a very prominent (vs. faint) dark spot at the base of the dorsal spine, a crescentic (vs. ovoid) dark humeral mark, and a dorsal fin with very elongate first and second rays and a markedly concave dorsoposterior margin (vs. with moderately elongate first and second rays and a straight or weakly concave dorsoposterior margin; Fig. 3). The black spot in front of the dorsal-spine base is also more prominent in preserved material of M. falcarius than in either M. cavasius or M. seengtee . Mystus falcarius further differs from M. cavasius in having more gill rakers (22-29 vs. 13-22; Table 1).

Description. Biometric data are given in Table 4. Head depressed; dorsal profile evenly sloping, and ventral profile almost straight. Bony elements of dorsal surface of head covered with thin skin; bones readily visible, especially on posterior half of neurocranium, and ornamented with numerous fine, radial grooves. Anterior cranial fontanelle extending from behind snout to line through posterior orbital margins, separated from posterior fontanelle by narrow epiphyseal bar. Posterior fontanelle extending to base of supraoccipital spine. Supraoccipital spine elongate, slender and with blunt tip; extending to anterior nuchal plate. Eye ovoid, horizontal axis longest; located entirely in dorsal half of head. Gill openings wide, extending from exposed surface of posttemporal to beyond isthmus at line through mouth corners. Gill membranes free from isthmus. First branchial arch with 22-29 long, slender gill rakers.

Mouth subterminal, fleshy upper lip extending anteriorly beyond upper jaw. Oral teeth small and villiform, 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 well past level of premaxillary band; band width narrower than premaxillary band at midline, widening laterally and then tapering to a sharp point posterolaterally.

Barbels in four pairs. Maxillary barbel long and slender, extending beyond caudal-fin base. Nasal barbel slender, extending to vertical through base of pectoral spine. Inner mandibular-barbel origin close to midline; thicker and longer than nasal barbel and extending to base of posteriormost pectoral-fin ray. Outer mandibular barbel originating posterolateral of inner mandibular barbel, extending to vertical through middle of dorsalfin base.

Body moderately compressed. 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. Lateral line complete and midlateral in position. Vertebrae 22+18=40 (1), 22+19=41 (2), 22+20=42 (11), 23+19=42 (8), 23+20=43 (5) or 23+21=44 (2).

Dorsal fin with spinelet, spine, and 7 (29) rays. Origin of dorsal fin anterior to midbody, about one-third of body. Dorsal fin margin markedly concave, with first two fin rays longer than others. Dorsal fin spine moderately long, straight and slender, posterior edge with 3-8 indistinct serrations. Serrations fewer, lower and less distinct in smaller specimens. Anterior nuchal plate acutely triangular.

Pectoral fin with stout spine, sharply pointed at tip, and 7 (6), 8 (10), 9 (10) or 10 (3) rays. Anterior spine margin smooth; posterior spine margin with 12-22 serrations along entire length (serrations fewer in smaller specimens). Pectoral fin margin straight anteriorly, convex posteriorly. Postcleithral (humeral) process short and slender, with concave dorsal edge and extending to anterior tip of anterior nuchal plate.

Pelvic fin origin at vertical through posterior end of dorsal-fin base, with i,5 (29) 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 short genital papilla reaching to base of first anal-fin ray.

Adipose fin with very long base and deeply-incised posterior portion, spanning almost all of postdorsal distance. Anal fin origin located at approximately middle third of adipose fin, fin with iv,6 (5), iv,7 (11), iv,8 (12) or iv,9 (1) rays and curved posterior margin.

Caudal peduncle moderately deep. Caudal fin deeply forked, with i,7,7,i (5), i,7,8,i (13), i,7,9,i (10) or i,8,9,i (1) principal rays; upper lobe slender and lanceolate, lower lobe pointed. Procurrent rays extending only slightly anterior to fin base.

Coloration. In 70% ethanol: dorsal surface of head and body uniform brownish gray. Very distinct dark spot in front of base of dorsal spine. Crescentic dark mark on humeral region, indistinct in some specimens. Ventral surfaces of head and body dirty white; adipose fin brownish gray. All fins hyaline, with melanophores on fin membranes on some individuals, usually more densely aggregated along margins with fin rays. Dorsal half of barbels gray dorsally, gradually turning to dirty white on ventral half and tips.

Distribution. Known from the Irrawaddy and Salween river drainages in Myanmar, as well as the shorter drainages in southern Myanmar (in the Tenasserim region; Fig. 4).

Etymology. From the Latin falx, meaning sickle, in reference to both the markedly concave dorsoposterior margin of the dorsal fin in this species and the crescent shaped humeral mark. Used as an adjective.