Exostoma dhritiae, Singh & Kosygin & Gurumayum & Rath, 2022

Singh, Pratima, Kosygin, Laishram, Gurumayum, Shantabala Devi & Rath, Shibananda, 2022, Exostoma dhritiae, a new sisorid catfish (Teleostei: Sisoridae) from the Brahmaputra River drainage, Arunachal Pradesh, India, Zootaxa 5219 (2), pp. 165-174 : 167-169

Exostoma dhritiae , new species

( Fig. 1 )

Type materials. Holotype. ZSI FF 9119, 52.8 mm SL, India: Arunachal Pradesh: Upper Siang District: Siking stream a tributary of Siang River near Yingkiong ( Brahmaputra River drainage), 28° 39' N; 95° 0' E, L Kosygin et al., 21 Nov 2021.

Paratypes. ZSI FF 9120, 6, 46.3-51 mm SL, same data as holotype.

Diagnosis. Exostoma dhritiae is distinguished from congeners in having a combination of the following characters: the presence of conical tubercles on the dorsal surface of the head, paired fin rays and anterior margin of dorsal fin spine; adipose-fin base distinctly separate from upper procurrent caudal-fin rays, its posterior extremity distinctly incised (dorsoposterior margin sharply angular); anterolateral surfaces of the lip with 3 to 4 parallel anastomosing plicae followed by numerous irregular rounded plaques; body depth at anus 13.4−17.6 % SL; adipose fin base length 23.1−34.3 % SL; caudal-peduncle length 16.5−21.0 % SL; caudal-peduncle depth 6.6−9.3% SL; tip of maxillary barbel reaching to base of fifth pectoral-fin ray; nasal barbel extending to posterior margin of eye; 10−11 branched pectoral-fin rays.

Description. Biometric data are in Table 1 . Head and body broad, strongly depressed. Rostral margin slightly truncate dorsally. Dorsal profile rising gently from internarial region to base of dorsal fin then elevating gently towards adipose fin, and sloping ventrally to base of caudal fin. Ventral profile flat to anal-fin base, then sloping gently dorsally to base of caudal fin. Mid-lateral region from pectoral-fin base to anal-fin base slightly depressed with swollen muscular margins. Anus and urogenital openings located midway between posterior end of pelvic fin and anal-fin origin.

Mouth inferior with broad, fleshy, papillate lips. Tooth patches on both jaws separated in midline. Most of premaxillary tooth patches exposed in closed mouth. Teeth in jaws distally flattened, oar-shaped deeply embedded in the skin. Teeth on lower jaw situated in two well-separated, roughly triangular patches. Palate edentulous. Lower lip with prominent labial fold, notched at insertions of inner mandibular barbels ( Fig. 2 ). Barbels four pairs, maxillary barbel dorso-ventrally flattened, with broad base and pointed tip extending to base of the fifth pectoral-fin ray, its ventral surface with adhesive pad consisting of 10−15 elongate plicae followed by series of small, roundedplicae. Nasal barbel long extending to posterior margin of eye, basally wide, dermal flap slender. Inner mandibular barbel short, originating at labial flap, originating from notch between median and lateral lobes of lower lip; outer mandibular barbel slightly flattened with pointed tip, not reaching to the pectoral fin origin. Maxillary and nasal barbel with numerous prominent conical tubercles. Anterolateral surfaces of lip with 3 to 4 parallel anastomosing plicae followed by numerous irregular rounded plaques ( Fig. 2 ). Eyes small, dorso-laterally situated, subcutaneous. Gill openings narrow, extending from base of first pectoral-fin ray to above dorsal much higher than the level of last pectoral-fin base. Dorsal and lateral side of head with numerous backwardly pointed conical tubercles ( Fig. 3 ).

Dorsal fin with i, 5 (1) or 6* (7) rays. Adipose-fin base long; its posterior margin distinctly separate from upper procurrent rays of caudal fin, and distinctly incised with the dorsoposterior margin sharply angular ( Fig. 4 ). Pectoral fin enlarged, without spine and with i,10 (5) or i,11 (2) rays; first ray greatly flattened, with numerous parallel striae on ventral surface, dorsal surface of fin with tubercles. Pelvic fin enlarged, with convex distal margin and i,5 (7) rays; first ray greatly flattened, with numerous parallel striae on ventral surface, its tip reaching anus when adpressed; dorsal surfaces of fin with tubercles. Anal fin with i,4 (3) or i, 5 (4) rays, dorsal surface of fin with tubercles. Caudal fin deeply emarginated with i,6,7,i (2) or i,8, 7, i*(5) rays, lower lobe slightly longer. Vertebrae 39.

Coloration. In 70 % ethanol, the dorsolateral surfaces of the head and body are brown, with pale cream on the ventral surfaces and the dorsal surface of the head with a distinct dark blotch near the occiput. The distal half of dorsal, pectoral, pelvic and anal fins hyaline, yellowish brown basally.Adipose fin yellowish, distally lighter. Caudal fin hyaline medially, pale brown basally and distally. Maxillary and nasal barbels are brownish and creamish-grey ventrally.

Distribution and habitat. Exostoma dhritiae is known only from the type locality Siking stream, a tributary of Siang River near Yingkiong (Brahmaputra River drainage), Upper Siang District, Arunachal Pradesh, India ( Fig. 5 & 6 ). The Siking stream is shallow, cold and swiftly flowing, with a substrate of cobbles and pebbles. The associated species include Garra spp. , Glyptothorax spp. , Pseudecheneis spp. , Schistura spp. , and Schizothorax spp.

Etymology. The new species is named after Dr Dhriti Banerjee, Director of the Zoological Survey of India, to honour her contribution to knowledge of the fauna of India.

Figures

FIGURE 1. Exostoma dhritiae, ZSI FF 9119, holotype, 52.8 mm SL: a, dorsal; b, lateral; and c, ventral aspects.

FIGURE 2.Ventral view of head showing oromandibular structure of Exostoma dhritiae, ZSI FF 9119, holotype, 52.8mm SL.

FIGURE 3. Lateral view of head of Exostoma dhritiae, ZSI FF 9119, holotype, 52.8mm SL, showing the conical tubercles.

FIGURE 4. Lateral view of posterior part of adipose fin of Exostoma dhritiae, ZSI FF 9119, holotype, showing separation from procurrent caudal fin rays and incised with sharply angular dorsoposterior margin.

FIGURE 5. Siking stream a tributary of Siang River near Yingkiong (Brahmaputra River drainage), the type locality of Exostoma dhritiae.

FIGURE 6. Map showing type locality of Exostoma dhritiae.

Tables

TABLE 1. Morphometric data for holotype (ZSI FF 9119) and 6 paratypes (ZSI FF 9120) of Exostoma dhritiae (ranges include holotype data).

	Holotype	Range	Mean	Sd
In % of standard length
Head length	22.2	22.0−26.3	23.0	1.5
Body depth at dorsal-fin origin	15.0	15.0−17.6	16.7	1.4
Body depth at anus	13.4	13.4−17.6	14.8	1.5
Predorsal length	39.2	38.5−42.0	40.4	1.3
Prepectoral length	17.8	17.8−19.7	18.7	0.6
Prepelvic length	48.5	45.4−48.5	47.4	1.2
Preanal length	76.1	64.4−76.1	71.8	3.7
Dorsal-fin height	19.9	16.0−19.9	17.8	1.8
Length of dorsal-fin base	10.0	9.7−12	10.6	0.7
Dorsal-to-adipose distance	8.7	8.7−14.3	12.2	1.9
Post-adipose distance	5.5	4.6−5.8	5.2	0.4
Length of adipose-fin base	34.3	23.1−34.3	28.2	4.7
Pectoral-fin length	23.1	20.3−23.3	22.4	1.1
Pelvic-fin length	19.7	16.8−20.1	18.6	1.3
Anal-fin length	14.0	12.8−14.3	13.4	0.8
Length of anal-fin base	6.1	5.8−7.7	6.3	0.8
Pectoral-pelvic distance	22.9	17.1−22.9	17.9	5.0
Length of caudal-peduncle	20.3	16.5−21.0	19.0	1.5
Depth of caudal-peduncle	7.4	6.6−9.3	8.0	0.8
Caudal-fin length	21.6	18.4−21.6	20.8	1.6
In % of head length
Head depth	54	46−54	52	3.1

......Continued on the next page