Pseudecheneis nagalandensis, Shangningam & Kosygin, 2020

Shangningam, Bungdon & Kosygin, Laishram, 2020, A novel species of sisorid catfish, Pseudecheneis nagalandensis sp. nov., (Teleostei: Sisoridae) from the Chindwin Basin of Nagaland, India, Records of the Zoological Survey of India 120 (2), pp. 105-111 : 106-108

Pseudecheneis nagalandensis sp. nov. ( Figure 1 )

Material examined: Holotype: 58.7 mm SL, India, Nagaland, Phek District, Tizu River at Sohomi ( Chindwin River basin), 25º45'N 94º29'E, 793m above sea level, 24- iii-2018, coll. BD Shangningam (ZSI FF 7679).

Paratypes. 7 specimens, 30.8−42.0 mm SL, same data as holotype one paratype (38.5 mm SL) dissected for osteology (ZSI FF 7680).

Diagnosis: Pseudecheneis nagalandensis sp. nov. is separated from its congeners in possessing the following blend of characters: 13−14 transverse ridges on the thoracic adhesive apparatus that separated by grooves; teeth on outer edge of both tooth bands exposed when mouth closed; pelvic fin extending to the anal-fin origin, 14 branched pectoral-fin rays; eye diameter 9.1−11.9% HL; snout length 46.4−59.5% HL; anal-fin length

18.3−21.7% SL; 36 total vertebrae.

Description: Morphometric data presented in Table 1. Dorsal profile rises steeply from snout tip to dorsal-fin origin, slightly straight till adipose-fin base then gently sloping ventrally to end of caudal peduncle. Ventral profile remains horizontal till anal-fin base then sloping gradually to end of caudal-fin origin. Caudal peduncle long and moderately elongated. Anus and urogenital openings located anterior to anal-fin origin, skin smooth, tuberculated sparsely on head, opercular and predorsal region, lateral line complete and mid-lateral,total vertebrae 36 comprising of 18 abdominal and 18 post-abdominal vertebrae, gill rakers on first branchial arch 10 (1).

Mouth inferior, with thin papillated lips gill opening moderate, extends from post temporal to slightly beyond base of pectoral fin.Head acutely triangle when viewed from above, ventral surface covered with unculiferous collar on distal margin of branchiostegeal membrane just anterior to thoracic adhesive apparatus. Thoracic adhesive apparatus comprised of 13−14 transverse ridges or laminae separated by grooves or sulcae; last 2−3 ridges not joining at midline of adhesive apparatus ( Figure 2 ). Adhesive apparatus extends from posterior of distal margin of branchiostegeal membrane to middle of last pectoral-fin ray.

Barbels flattened, four pairs. Major portion of maxillary barbel joins snout through a flap of skin, ventral surface with papillae, distal tip nearly reaching to level of anterior rim of eye. Nasal barbel not reaching midway between posterior nare and anterior margin of eye,base covered with a diminutive flap of skin. Inner mandibular barbel short, distal tip not reaching end of branchiostegal membrane outer mandibular barbel extends to level of anterior margin of eye, its origin postero-lateral to inner mandibular barbel; eye minute, subcutaneous, located on dorsum of head.

Teeth arranged in irregular rows, embedded in skin with tips exposed, prominent at their outer edges. Outer teeth shovel shaped and inner teeth conical. Premaxillary tooth band semi-circular with two spatulate and one to four incisiform teeth along its outer edge. Dentary tooth band crescentic with three large teeth along its outer edge. Teeth on outer edge of both tooth bands exposed when mouth closed.

Dorsal fin with i, 6(8) rays, origin located at point through anterior third of body, margin straight. Adipose-fin base long, 17.7−21.0 % of standard length, longer than anal-fin base, situated closer to dorsal-fin origin than to caudal-fin base. Pectoral fin with i, 14(8) rays long, almost reaching end of pelvic-fin base. First undivided ray not ossified, ventral surface with regular striae. Pelvic fin with i, 5(8) rays, origin opposite to base of fifth branched dorsal-fin ray. Pelvic fin separated by a short gap, as wide as 1.0−1.6 eye diameter. First unbranched ray of pelvic fin broadened, ventral surface covered with 18−32 prominent regular plicae ( Figure 3 ). Anal fin with iii, 8(8) rays, outer rays longer, extending to level of posterior of adipose fin. Caudal fin deeply forked with i,7, 8, i(8) principal rays, tip of lobes pointed, lower lobe slightly longer.

Sexual dimorphism: In both sex, urogenital papillae located immediately posterior to anus. Males with a squarish shaped papilla, its apex pointing posteriorly ( Figure 4a ). Females with flat, comparatively smaller papillae, bilobed and a small rounded mid-ventral posteriorly projecting lobe ( Figure 4b ).

Coloration: In preservative, body dark brown on dorsal and lateral surface. Ventral part of body and head slightly creamish yellow. Body with distinct sequence of pale yellowish saddles or patches: first small patches located on dorsal-fin origin, second saddle across end of dorsal-fin base; third saddle with three patches across adipose-fin origin and fourth saddle at end of adipose fin. Adipose - fin brown, distal margin yellowish. Dorsal surface of paired fins brown with yellowish band on inner half and distal margin hyaline. Median fins with pale yellow band at middle, and hyaline distal margin. Caudal fin brown, middle and distal tip of both lobes tinged yellow.

Distribution: Pseudecheneis nagalandensis is currently known to have distributed only in the type locality, Tizu River, Nagaland, India.

Habitat: Tizu River ( Figure 5 ), the type locality of Pseudecheneis nagalandensis has predominantly riffle habitat with rocky substratum and cool water. The species was found attached to bottom of stone when collected. Some other fish species belonging to the genera Psilorhynchus , Glyptothorax, Garra and Schistura are found in the same locality.

Etymology: The species is christened after Nagaland state, its type locality.

Figures

Figure 1. Pseudecheneis nagalandensis sp. nov., holotype, ZSI FF 7679, 58.7 mm SL; a. dorsal, b. lateral and c. ventral view.

Figure 2. Thoracic adhesive apparatus of Pseudecheneis nagalandensis sp. nov., showing laminae and sulcae.

Figure 3. Pelvic fin of Pseudecheneis nagalandensis sp. nov., showing presence of plicae.

Figure 4. Genital papilla of Pseudecheneis nagalandensis sp. nov., a. male, ZSI FF 7679, 58.7 mm SL; b. female ZSI FF 7680, 36.1 mm SL.

Figure 5. Tizu River, type locality of Pseudecheneis nagalandensis.