A new diminutive subterranean eel loach species of the genus Pangio (Teleostei: Cobitidae) from Southern India Author Arjun, C. P. Author Sidharthan, Arya 0000-0002-4398-1895 Faculty of Ocean Science and Technology, Kerala University of Fisheries and Ocean Studies (KUFOS), Kochi, India arya @ kufos. ac. in; https: // orcid. org / 0000 - 0002 - 4398 - 1895 & Zoo Outreach Organization (ZOO), Coimbatore, India arya@kufos.ac.in Author Dahanukar, Neelesh 0000-0001-7162-9023 Department of Life Sciences, School of Natural Sciences, Shiv Nadar University, Delhi-NCR, India. neelesh. dahanukar @ snu. edu. in; https: // orcid. org / 0000 - 0001 - 7162 - 9023 neelesh.dahanukar@snu.edu.in Author Raghavan, Rajeev Department of Fisheries Resource Management, Kerala University of Fisheries and Ocean Studies (KUFOS), Kochi, India Malabar Awareness and Rescue Centre for Wildlife (MARC), Kannur, India text Zootaxa 2022 2022-05-16 5138 1 89 97 journal article 110547 10.11646/zootaxa.5138.1.9 c97c0dee-3c05-42bb-a6c6-dc6c28dcc55f 1175-5326 6552241 EB44E1E7-AC37-445B-A0EB-D89219180C6F 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. TABLE 1. Morphometric data of Pangio pathala type series, and additional material of P. bhujia from the new locality

Characters	Pangio pathala		Pangio bhujia
Holotype	Paratype	Additional population		Type material
( Anoop et al . 2019 )
KUFOS. FT.2020.1	KUFOS. FT.2020.2	KUFOS. FT.2020.3	KUFOS FC.2020.1	KUFOS FC.2020.2	Mean (SD)	Range
Total length (mm)	34.4	20.7	23.5	22.2	24.5	27.8 (1.2)	26.5–29.7
Standard length (SL, mm)	32.1	18.9	22.3	19.7	22.3	25.0 (0.9)	23.6–26.4
% SL
Head length (HL)	10.5	13.1	11.3	12.9	13.1	11.9 (0.6)	10.8–12.6
Pre-anal length	70.2	71.9	70.8	67.6	69.3	71.3 (2.6)	67.8–75.8
Body depth	5.5	6.1	7.1	8.3	7.6	8.3 (0.6)	7.5–9.3
Body width	4.0	5.7	4.0	4.7	4.4	5.1 (0.6)	3.9–5.8
Caudal-peduncle depth	7.0	5.9	4.4	6.8	7.1	7.3 (1.1)	5.8–8.8
Caudal-peduncle length	26.1	23.7	23.7	27.9	25.4	25.8 (1.7)	23.5–28.5
Caudal-peduncle width	1.6	2.4	1.8	1.8	2.5	1.8 (0.1)	1.6–2.0
Pectoral-fin length	7.3	7.5	7.3	7.3	8.7	8.4 (1.0)	7.0–9.7
Snout length	3.5	4.8	3.8	4.3	4.4	4.6 (0.5)	4.1–5.5
Eye diameter	0.5	0.9	0.6	0.7	0.8	0.7 (0.1)	0.6–0.8
% HL
Snout length	34.3	36.4	34.0	33.6	36.3	38.5 (4.4)	34.4–45.5
Eye diameter	4.8	6.5	5.6	5.2	6.8	6.2 (0.6)	5.2–7.3

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. FIGURE 1. Pangio pathala holotype (KUFOS.FT.2020.1, 32.1 mm SL) (A) in life, and (B–F) in preservative. 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 ). FIGURE 2. Distribution map of subterranean Pangio species in Kerala, India TABLE 2. Percentage raw genetic distances (co1 gene) of members of the genus Pangio . Diagonal values in bold are intra-specific distances.

Species	[1]	[2]	[3]	[4]	[5]	[6]	[7]	[8]
Pangio pathala	[1]	0.0
Pangio bhujia	[2]	8.1–8.7	0.2–2.0
Pangio ammophila	[3]	14.4	15.4–15.7	0.0
Pangio anguillaris	[4]	16.0–16.4	15.5–16.7	16.7–17.3	3.0
Pangio kuhlii	[5]	18.9–19.0	17.6–18.7	17.1–17.3	15.3–15.7	0.2
Pangio cuneovirgata	[6]	18.1	17.8–18.0	17.6	14.2–16.5	7.7	0.0
Pangio oblonga	[7]	19.2	18.8–19.1	20.7	15.0–15.4	10.5–10.6	9.3–9.4	0.0
Pangio pangia	[8]	18.8–19.5	18.4–19.8	17.6–18.6	13.0–15.6	10.2–11.4	7.9–9.1	9.0–10.1	0.3–2.8

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 .