Pangio pathala, Arjun & Sidharthan & Dahanukar & Raghavan, 2022

Arjun, C. P., Sidharthan, Arya, Dahanukar, Neelesh & Raghavan, Rajeev, 2022, A new diminutive subterranean eel loach species of the genus Pangio (Teleostei: Cobitidae) from Southern India, Zootaxa 5138 (1), pp. 89-97 : 90-93

Pangio pathala , new species

( Fig. 1 )

Holotype. KUFOS.FT.2020.1, 32.1 mm SL; India: Kerala: Thiruvanvandoor (9°20’23.09”N, 76°34’48.54”E), 7 m asl., coll. R. Sundar, A. Sidharthan & C. P. Arjun, 25 October 2020.

Paratype. KUFOS.FT.2020.2 (c&s), 18.9 mm SL; same data as holotype ; KUFOS.FT.2020.3, 22.3 mm SL; India: Kerala: Thiruvanvandoor (9°20’23.09”N, 76°34’48.54”E), 7 m asl., coll . R. Sundar, A. Sidharthan & C. P. Arjun, 11 November 2020 .

Diagnosis. Pangio pathala is distinguished from all other species of Pangio (except P. bhujia ) by the absence of the dorsal fin (vs. presence), presence of four pectoral-fin rays (including an unbranched rudimentary ray) (vs. 5–11), 13 segmented (both branched and unbranched) caudal-fin rays (vs. 14–16), and a unique count of 27 caudal vertebrae (vs. 11–20), the highest among the known members of the genus. Pangio pathala is further distinguished from all other species of Pangio except P. bhujia , P. fusca , P. apoda , P. pulla and P. lidi by the absence of pelvic fins. Pangio pathala differs from its only subterranean congener, P. bhujia , in having four pectoral-fin rays (vs. three); five anal-fin rays (vs. six); greater number of vertebrae (67 vs. 62–63); and a raw genetic distance of 8.1–8.7% in the mitochondrial co1 gene.

Description. Morphometric and meristic data are presented in Table 1 . Body elongate, oval in cross section, strongly compressed laterally in caudal region.Standard length 14.2–18.2 times body depth; body depth 1.1–1.8 times body width. Caudal peduncle laterally compressed, long, its length 3.6–5.4 times its depth, its depth 2.4–4.4 times its width. Precaudal adipose keels well-developed, deep, long; dorsal adipose keel originating anterior to vertical from anal-fin origin; adipose keel of ventral profile originating immediately posterior to anal-fin base. Scales absent.

Head rounded, small, about 10.5–13.1% SL. Eyes small, 4.8–6.5% HL. Mouth subterminal; with three pairs of elongated barbels. Two pairs of maxillary barbels, outer maxillary barbel reaching beyond posterior border of eye; inner maxillary barbel reaching between eye and nare. One pair of mandibular barbels, reaching anterior border of eye. Posterior margin of anterior naris developed into a long (47.53–58.61% HL), pointed flap, referred to as nasal barbel.

Pectoral fin narrow, long, thread-like, with four rays including an unbranched rudimentary ray. Anal fin short with rounded margin, with one rudimentary ray followed by four unbranched rays. Pelvic fin and girdle absent. Dorsal fin and dorsal-fin pterygiophores absent. Caudal fin pointed, with both segmented and unsegmented, but unbranched rays: 4 dorsal unsegmented +6 dorsal segmented + 7 ventral segmented + 2 ventral unsegmented rays. Ribs on vertebrae 5–40. Total vertebrae 67 = 40 abdominal + 27 caudal vertebrae.

Colouration. In life, body pinkish-red to light pink when freshly collected, becomes brownish pink in captivity, slightly darker on dorsal profile, ventral profile translucent. Eye a tiny small black spot. Caudal region translucent, rendering caudal vertebrae visible. Pectoral, anal, and caudal fins hyaline ( Fig. 1a ). In preservative, body pale yellowish-white with tiny black eye. Dorsal side of head and body with scattered minute melanophores only visible at 20× magnification.

Distribution and habitat. Currently, Pangio pathala is known only from its type locality, Thiruvanvandoor, near the town of Chengannur, Kerala State, India ( Fig. 2 ). Specimens were collected from an overhead water-storage tank connected to an old dug-out well using an electric water pump. The well is approximately 17 feet deep, and drawn water was used for drinking and household activities ( Fig. 3 ).

Etymology. The species name is based on the Sanskrit word pâtâla, which means ‘below the feet’, denoting the subterranean realms of the universe—which are located under the earth’s surface. A noun in apposition.

Genetic analysis. In the maximum likelihood analysis based on the co1 gene, Pangio pathala and P. bhujia are sister species and form a clade with the other Western Ghats congeners ( Fig. 4 ). Pangio pathala differs from P. bhujia by a raw genetic distance of 8.1–8.7%, and from all its other congeners for which genetic data (mitochondrial co1) are available, by a raw genetic distance of 14.4–19.5% ( Table 2 ).

New distribution record for Pangio bhujia . We also take this opportunity to record two specimens of P. bhujia from Indianoor (10°58’56.20”N, 76°2’32.51”E, 37 m. asl) near the town of Kottakkal. The two fish were collected from a shallow channel (<0.1 m depth) originating in a nearby pond (<2 m depth) used for irrigation. The substrate of the channel comprised of laterite soil covered by fallen, decayed leaves. The habitat is similar to the type locality of P. bhujia , which is located around 40 km north. Detailed morphological examination of the specimens, and comparison of its co1 gene sequence, confirmed its conspecificity with P. bhujia ( Table 1 and Fig. 4 ). Co-occurring species in the channel and pond include Lepidocephalichthys thermalis , Pseudosphromenus cupanus , Rasbora dandia , Aplocheilus lineatus , and Puntius vittatus .

Figures

FIGURE 1. Pangio pathala holotype (KUFOS.FT.2020.1, 32.1 mm SL) (A) in life, and (B–F) in preservative.

FIGURE 2. Distribution map of subterranean Pangio species in Kerala, India

FIGURE 3. Habitat of Pangio pathala—an old dug-out well at Thiruvanvandoor, Kerala, India

FIGURE 4. Maximum likelihood phylogenetic tree of the genus Pangio based on mitochondrial co1 gene. Lepidocephalichthys thermalis is used as outgroup. Values along the nodes are percentage bootstraps based on 1000 iterations.