Glyptothorax distichus, Kosygin & Singh & Gurumayum, 2020

Kosygin, Laishram, Singh, Pratima & Gurumayum, S. D., 2020, Glyptothorax distichus, a New Species of Catfish (Teleostei: Sisoridae) from Mizoram, North-Eastern India, Records of the Zoological Survey of India 120 (1), pp. 25-32 : 26-27

Glyptothorax distichus sp.nov.

( Figure 1 )

of adhesive apparatus not extending anteriorly onto gular region; absence of plicate on ventral surfaces first pectoral and pelvic fins rays, smooth skin on head and body; presence of two broad pale cream longitudinal stripes on body; and 20 + 17 Vertebrae.

Description: Morphometric data as in Table 1 Body elongate. Head depressed with almost conical snout when viewed dorsally. Dorsal profile rising evenly from tip of snout to origin of dorsal fin, then sloping gently from there to end of caudal peduncle. Occipital process not in contact with anterior nuchal plate elements. Ventral profile flat till posterior end of pectoral fin base, then slightly convex till anterior end of pelvic fin base, and then rising gently from anterior end of pelvic fin base to end of caudal fin base. Caudal peduncle moderately deep. Mouth inferior, lips papillate, teeth on upper jaw as one continuous band with anterior margin almost truncate; those on lower jaw in two patches, separated by a narrow partition. Eyes small and round, located on dorsal surface of head.

Thoracic adhesive apparatus chevron-shaped, slightly longer than broad, extending from isthmus to middle of pectoral fin base with poorly developed chevron-shaped median depression that is widely opened posteriorly by skin ridges ( Figure 2 ). Striae of thoracic adhesive apparatus uninterrupted, medial striae oriented anteriorly, lateral ones anterolaterally. Anus and urogenital openings located at vertical through posterior end of adpressed pelvic fin. Skin on head and body almost smooth. Lateral line complete and midlateral. First branchial arch bearing 2+9 (1) or 3+8 (1) gill rakers. Vertebrae 20 + 17 = 37 (2).

Material examined: Holotype: ZSI FF 5390, 101.1 mm SL; India: Mizoram: Aizawl district: Tlwang River near Sairang (Barak-Meghna-Surma drainage), 23°48'26" N 92°38'45"E; Coll. L. Kosygin, 24-ix-2007 . Paratypes: ZSI FF 5391, 1, 78.0 mm SL; same data as holotype .

Diagnosis: Glyptothorax distichus is diagnosed from congeners in the Indian subcontinent in having a combination of the following characters: a chevron-shaped thoracic adhesive apparatus, with poorly developed median depression that is widely opened posteriorly by skin ridges; short dorsal fin spine (10.4, 12.4% SL); deep body (depth at anus 12.7, 13.2% SL); short caudal peduncle (17.6, 16.3% SL vs. 21.4–23.9); slender caudal peduncle (7.8, 7.9% SL); short predorsal length (32.7, 34.2% SL) unculiferous ridges Barbels in four pairs. Maxillary barbel long and slender, reaching ends of pectoral fin base. Outer mandibular barbel longer than inner, slightly exceeding base of pectoral fin spine base. Inner mandibular barbel not reaching operculum. Nasal barbel short, not reaching anterior margin of eye when adpressed, extending halfway to orbital margin.

brown with pale creamish posterior edge. Pectoral, pelvic, anal and caudal fins dusky with hyaline margins.

Distribution: Presently known only from the type locality, the Tlawng River near Sairang, Aizawl District, Mizoram (Barak-Meghna-Surma drainage), India ( Figure 4 ).

Dorsal fin located halfway between snout tip and adipose-fin origin, with I, 6 rays. Dorsal fin spine strong, gently curved, serrated posteriorly, shorter than depth of body immediately ventral. Adipose-fin short, anterior margin straight, posterior margin convex. Pectoral fin slightly shorter than head, with I, 9, i rays. Pectoral fin spine broad, anterior margin smooth, posterior margin with 10–12 serrae without furrow at approximate juncture of anterior and posterior portions of each fin-spine element ( Figure 3 ). Pelvic fin with I, 5 rays, not reaching the origin of anal fin when adpressed. Ventral surface of paired-fins not pleated. Anal fin long, with II, 8, i rays, originating at vertical slightly posterior to adipose-fin origin. Caudal fin forked, with 17 or 15 rays.

Etymology: The species name comes from the Latin 'distichus' meaning having two longitudinal rows of grain or lines, in allusion to the two broad longitudinal stripeson the body. An adjective.

Coloration: In 70% alcohol: Dorsal and lateral surfaces of head and body dark brown, fading to pale cream ventrally. Two broad pale cream longitudinal stripes: one mid-dorsal, originating from end of dorsal fin base and another midlateral (width 17.1, 22.1% body depth at anus) originating from operculum to the caudal fin base on either side of body. Dorsal fin with a distinct broad blackish brown band at distal half. Adipose-fin dark

Figures

Figure 1. Glyptothorax distichus, ZSI FF 5390, holotype, 101.1 mm SL; India: Mizoram: Tlawng River; dorsal, lateral and ventral views.

Figure 2. Thoracic adhesive apparatus of Glyptothorax distichus, ZSI FF 5390, holotype, 101.1 mm SL.

Figure 3. Ventral surface of pectoral fin spine of Glyptothorax distichus, ZSI FF 5391, paratype, 78.0 mm SL.

Figure 4. Tlwang River at Sairang, Mizoram, type locality of Glyptothorax distichus.