Mystus irulu, Vijayakrishnan & Praveenraj, 2022

Vijayakrishnan, Balaji & Praveenraj, Jayasimhan, 2022, Mystus irulu, a new species of bagrid catfish from the Western Ghats of Karnataka India (Teleostei: Bagridae), Zootaxa 5120 (3), pp. 443-448 : 444-446

Mystus irulu , new species

( Fig. 1 , 2 , 3 )

Holotype. ZSI/ MBRC /F- 2486, 120 mm SL; India, Karnataka, Netravathi River near Uppinangady Town; 12°50.57’ N, 75°18.29’ E; 28 m asl.; Thiyagaraja and team, 27 January 2021.

Paratype. ZSI/ MBRC /F- 2487, 116 mm SL; CIARI /FF- 85, 128 mm SL, cleared and stained. Collection data same as holotype .

Diagnosis. Mystus irulu can be distinguished from all its South Asian congeners except M. leucophasis by possessing a uniformly black colour pattern. Mystus irulu can be readily distinguished from M. leucophasis in having a longer adipose-fin base (reaching base of the last dorsal-fin ray anteriorly vs. not reaching), a longer cranial fontanel reaching the base of the occipital process (vs. not reaching), lacking (vs. having) a filamentous extension of the upper principal-ray of the caudal fin and a shorter dorsal-fin spine (17.5–18.7% SL vs. 21.7–26.1).

Additional characters distinguishing it from related South Asian congeners are provided in the discussion.

Description. Head depressed, dorsal profile slightly convex up to level of posterior fontanel, then evenly sloping at angle of 20–25° to horizontal. Ventral profile slightly convex up to pelvic fin origin, almost straight after it. Bony elements of dorsal surface of head covered with thin skin; bones readily visible, especially on posterior half of neurocranium, ornamented with numerous fine, radial grooves. Midline of cranium with elongate fontanel extending from behind snout to base of supraoccipital spine. Anterior fontanel short with shallow cavity, posterior fontanel elongated. Supraoccipital process elongate, with gently converging sides, its tip blunt; extending to anterior nuchal plate. Eye ovoid, horizontal axis longest, its margin free; located entirely in dorsal half of head. Gill openings wide, extending from posttemporal to beyond isthmus. Gill membranes free from isthmus. Six branchiostegal rays. First branchial arch with 6+18 (1) gill rakers. Mouth subterminal, upper lip fleshy, upper lip extending anteriorly beyond upper jaw. Oral teeth small, villiform, in irregular rows on all tooth-bearing surfaces. Premaxillary teeth irregularly arranged in 2–3 rows, tooth band curved. Dentary tooth band narrower than premaxillary tooth band at symphysis, tapering laterally. Barbels in four pairs. Maxillary barbel long, moderately thick, extending to vertical through posterior of anal-fin base. Nasal barbel slender, extending to midway between posterior orbital margin and dorsal-most point of gill opening. Inner mandibular-barbel origin close to midline; barbel slender, extending to level of pectoral-fin origin. Outer mandibular barbel originating posterolateral of inner mandibular barbel, extending to midway between base of last pectoral-fin ray and pelvic-fin origin.

Body slightly compressed, becoming more so toward caudal peduncle. Dorsal profile rising evenly from tip of snout to origin of dorsal fin, sloping gently ventrad from origin of dorsal fin to end of caudal peduncle. Ventral profile slightly convex to anal-fin base, then sloping slightly dorsad to end of caudal peduncle. Caudal peduncle moderately deep. Skin smooth. Lateral line complete, midlateral in position. Vertebrae 23+18=41(1). Dorsal fin with one spine, 7 (3) rays. Dorsal-fin margin convex, anterior branch of fin rays longer than other branches. Dorsalfin spine short, straight, slender, posterior edge smooth. Pectoral fin with stout spine, sharply pointed at tip, 8 (2) or 9* (1) rays. Anterior spine margin smooth; posterior spine margin with 10–11* large serrations along entire length. Pectoral-fin margin straight anteriorly, convex posteriorly. Pelvic-fin with origin at vertical through mid-way of dorsal-fin base, with i, 5 (3) rays, 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 genital papilla reaching almost to base of first anal-fin ray. Adipose fin with convex margin for entire length, posterior portion deeply incised, origin in contact with base of last dorsal-fin ray; base long, extending most of postdorsal distance. Anal-fin base ventral to posterior half of adipose fin, with ii, 8 (3) rays, its posterior margin curved.

Caudal fin deeply forked, with i, 8+9, i (3) principal rays; dorsal lobe slightly pointed at tip, ventral lobe pointed at tip; procurrent rays extending slightly anterior to fin base.

Colouration. In life ( Fig. 2 ). Overall body colour black, except belly, with few silvery tinges. In preservative ( Fig. 1 ): Body blackish-grey, fading to lighter grey or brown on ventral surfaces. All fins greyish. Barbels dark grey.

Distribution and Ecology. Mystus irulu is presently known only from the Netravathi River system in Karnataka. The river at the type locality was deep and slow flowing with moderately clear water; the river bed consisted of sand, mud and pebbles. Other species encountered in the type locality were Etroplus canarensis , Garra sp. , Hypselobarbus jerdoni, Barilius sp. and Dawkinsia sp.

Etymology. The specific name irulu is derived from Kannada (the official language of the state of Karnataka), meaning dark, in reference to the uniformly black colouration of this species. Used as an adjective.

Figures

FIGURE 1. Mystus irulu, A. holotype, ZSI/MBRC/F-2486, 120 mm SL; lateral, dorsal and ventral views, B. Paratype, ZSI/ MBRC/F-2487, 116 mm SL, lateral view.

FIGURE 2. Mystus irulu, paratype, ZSI/MBRC-2487, 116 mm SL, colouration prior to preservation. Photo by Pranav Joshi.

FIGURE 3. Dorsal-fin profile of A. Mystus irulu, paratype, ZSI/MBRC/F-2487, 116 mm SL, B. M. cavasius, CIARI/FF-87, 159 mm SL, C. M. seengtee, CIARI/FF-88, 94.7 mm SL. (Dotted line showing the shape of the dorsal fin.)