Glyptothorax heokheei Singh & Chowdhury & Gurumayum & Kosygin 2023, new species

Glyptothorax heokheei, new species

(Figs. 1, 2a)

Type materials. Holotype, ZSI FF 9555, 152.0 mm SL, India: Arunachal Pradesh: East Siang District: Siku stream near Mebo, a tributary of the Siang River (Brahmaputra River drainage); 28°9’14″N, 95°22’ 47″E, S.D. Gurumayum, 25 Feb. 2020.

Paratypes. ZSI FF 9556, 4 ex., 102.4–124.1 mm SL, same data as holotype.

Diagnosis. Glyptothorax heokheei is diagnosed from all congeners in having a unique combination of the following characters: a chevron-shaped thoracic adhesive apparatus extending anteriorly onto gular region with more or less pointed anterior apex at isthmus, unculiferous striae prominent anteriorly from tip of median depression (Fig 2); body depth at anus 12.8–14.1% SL; head length 25.1–28.8 % SL; interorbital width 12.0–20.0 % HL; post-adipose distance 16.0–18.4 % SL; posterior margin of pectoral-fin spine with 14–18 serrae; nasal barbel not reaching anterior margin of eye; arrow-shaped anterior nuchal plate element; ventral surface of pectoral spine and first pelvic-fin ray non-plaited; 9–10 branched anal-fin rays; vertical through pelvic-fin origin posterior to base of last dorsal-fin ray, head and body mottled with dark brown spots and smooth skin.

Description. Morphometric data presented in Table 1. Body elongate. Head depressed with almost conical snout when viewed dorsally. Dorsal profile rising evenly from tip of snout to dorsal fin origin, then sloping gently to end of caudal peduncle. Occipital process not in contact with anterior nuchal plate. Anterior nuchal plate broad, arrow-shaped extensions when viewed dorsally. Ventral profile almost flat up to posterior end of pelvic-fin base, then slightly convex to end of caudal-fin base. Caudal peduncle moderately shallow. Mouth inferior, lips papillate, teeth on upper jaw as a continuous band, its anterior margin almost rounded; teeth on lower jaw in two patches, separated by wide partition. Eyes small, round, located on dorsal surface of head. Anus and urogenital opening located at vertical through posterior half of adpressed pelvic-fin. Skin smooth. Lateral line complete and mid-lateral. Gills on first branchial arch long, bearing 4+8 or 5+8 rakers.

Thoracic adhesive apparatus consisting of unculiferous ridges present over chevron-shaped field and pointed anteriorly at isthmus. Unculiferous striae orientated longitudinally, except for posteriormost lateral ridge, which is slightly tilted towards midline of body, prominent anteriorly from tip of central median depression transversely. Median longitudinal striae extending anteriorly along ventral midline of body to cover gular region (Fig. 2a). Median depression poorly developed, without unculiferous striae.

Barbels in four pairs. Maxillary barbel shorter than head length, slender, extending to middle of pectoral-fin base. Outer mandibular barbel longer than inner, extending to anterior margin of pectoral fin base. Nasal barbel slender, not reaching anterior margin of orbit when adpressed, extending to half distance between its base and anterior orbital margin.

Dorsal-fin located equidistant between snout tip and adipose fin origin, with ii, 6 (5) rays; its height greater than body depth at dorsal-fin origin. Dorsal-fin spine strong, almost straight, strongly rugose posteriorly with 11–17 ridges, and smaller than depth of body at its origin. Adipose-fin low, with anterior margin straight and posterior margin slightly convex, deeply incised with the dorsoposterior margin uniformly convex and attached to body. Pectoral fin shorter than head, with i, 8 (2) or i, 9 (2) or 10 (1) rays; its posterior margin concave. Pectoral-fin spine broad, long; its anterior margin smooth, and its posterior margin with 14–18 serrae. Pelvic-fin with i, 5 (4) or i, 6 (1) rays, its tip not reaching anal-fin origin when adpressed. Vertical through pelvic-fin origin posterior to vertical through posterior end of dorsal-fin base. Ventral surface of pectoral-fin spine and first pelvic-fin ray not plaited. Anal fin long, with iv, 9 (4), or iv, 10 (1) rays; its origin almost vertically opposite to adipose-fin origin. Caudal fin deeply forked, with 8 + 9 (5) branched rays.

Coloration. In 70% alcohol, dorsal surface of head and body yellowish brown; lateral surface light brown, fading to yellowish cream ventrally. Dorsal and lateral surfaces of head and body are mottled with dark brown spots. Anterior nuchal plate element is visible as a distinct yellowish arrow when viewed dorsally. Adipose fin pale yellow with dark brown base. Dorsal fin with an indistinct black band on distal half. Pectoral, pelvic, anal and caudal fins are dusky or mottled with dark brown spots.

Distribution. Glyptothorax heokheei is presently known only from the type locality, Siku stream near Mebo, a tributary of the Siang River, Brahmaputra drainage, East Siang District, Arunachal Pradesh, India (Fig. 3).

Etymology. The species is named after Heok Hee Ng of the Lee Kong Chian Natural History Museum, National University of Singapore (NUS), honouring his valuable contributions to the taxonomy and systematics of Asian catfishes.