Apterichtus kanniyakumari, Rasheeq & Kodeeswaran & Kathirvelpandian & Ajith Kumar, 2025

Rasheeq, Ahamed, Kodeeswaran, Paramasivam, Kathirvelpandian, Ayyathurai & Ajith Kumar, T. T., 2025, Apterichtus kanniyakumari, a new species of finless snake eel (Anguilliformes: Ophichthidae) from the Arabian Sea, Zootaxa 5696 (2), pp. 260-268 : 261-266

Apterichtus kanniyakumari sp. nov.

( Figures 1 , 2 , 3 Table 1)

LSIDurn:lsid:zoobank.org:act: BE7D652A-3D02-4F56-8630-99CFAF3D44E1

Holotype: NBFGR / OPHAKAN, 365 mm TL, unsexed, Colachel , Arabian Sea , depth 100 m, collected by Ahamed Rasheeq. A, 17 August 2024.

Paratype: NBFGR / OPHAKAN. 1, 367 mm TL, unsexed, taken along with the holotype .

Diagnosis. A moderate sized new species of Apterichtus is distinguished from its congeners by having the following combination of characters: head length 9.6–9.7, tail length 1.8–1.9, body depth at gill opening 42.1–54.8 in TL; anterior eye margin at tip of lower jaw, 3 preopercular and 9 supratemporal pores, 5+7 on infraorbital; teeth conical, uniserial in jaw, 1 vomerine tooth; body golden yellowish colour when fresh; mean vertebral formula 52- 131.

Description. Comprehensive counts and measurements are given in Table 1. In the text below, the asterisk denotes the holotype value. Body elongate ( Fig. 1 ), cylindrical, pointed at both ends, body depth at gill opening 42.1* (54.8) times in TL. Head length 9.6* (9.7) in TL, 13.6* (13.4) in trunk length. Snout tip sharply pointed, eye diameter 1.7* (1.4) in snout length; short median groove centrally on tip of underside of snout; slope of dorsal surface of snout approximately 30° relative to ventral side of snout. Anterior nostril with short tubular flap; posterior nostril oval shaped positioned before anteroventral margin of eye. Eyes moderate in size, 3.5* (3.2) in upper jaw and 9.9* (8.8) in HL. Rictus well behind posterior eye margin. Branchial opening high reaching mid quarter of body parallel to posterior eye margin, ventral, anterior margins converging but not connected.

Head pores ( Fig. 4 ) minute; 1+6 on supra-orbital, 5+7 on infra-orbital, 7 on lower jaw, 3 on preopercle, 9 on supra-temporal. Lateral-line pores small and evident before anus ( Table 1).

Teeth small, uniserial, conical and slightly recurved; larger intermaxillary teeth arranged in chevron of 5–8 teeth partially evident when mouth closed. Vomerine with single tooth on anterior most. Lower jaw with 19–24 teeth in each side and upper jaw with 20 teeth in each side, paratype with 17–26 teeth in each side and lower jaw with 23–25 teeth in each side ( Fig. 5 ).

Measurements (in mm) of the holotype. Total length (TL) 365; head length (HL) 38.0; trunk 130.3; tail 196; body depth at gill openings 8.7; body width at gill openings 5.8; body depth at anus 5.6; body width at anus 5.8; head depth at branchial basket 8.5; head width at branchial basket 5.8; snout length 6.4; tip of snout to rictus 13.3; tip of snout to lower jaw 2.2; eye diameter 3.8; interorbital distance 3.1; gill opening length 6.2; isthmus width 0.98.

Colouration. In life. Golden yellowish colour with minute melanophores along body, three black patches along lateral side of head surrounded by greyish white colour blotch immediately behind eye covering few infraorbital pores along upper jaw followed by second blotch along rictus origin of upper and lower jaw followed by first blotch behind lower jaw visible in both ventral and lateral side followed with a yellowish line running along lower jaw tip. Head with melanophore-less area on snout and lower jaw. Lower jaw white coloured ( Fig. 1 , 2 ).

In formalin. Body turned darker, faded and brown, black blotches still intact ( Fig. 3 ).

Distribution. Indian Ocean: known only from off Colachel, Tamil Nadu, Arabian Sea.

Etymology. The species is named “kanniyakumari ” (a noun in apposition), referring to the Kanniyakumari region of Tamil Nadu, India, which includes Colachel - the type locality and collection site of the holotype. The name honors the region’s historical, cultural, linguistic and geographical significance, as it was part of ancient Tamilakam, which flourished during the Sangam era.

Molecular analyses. Since the availability of sequences for this group is rare due to difficulty and rare in collections. The present molecular analyses encompass a few sequences ( Fig. 6 ) based on partial mitochondrial CO1 gene sequences analyzed using K2P model, Apterichtus kanniyakumari shows a genetic divergence of 12.1% from its sympatric species A. nanjilnaduensis (sequence generated in the present study), 13.4% from A. nariculus , 14.6% from Apterichtus flavicaudus ( Snyder, 1904) , and 21% from A. klazingai .

Remarks. The total numbers of preopercular and supratemporal pores are the key diagnostic characteristics of the genus Apterichtus ( McCosker & Hibino 2015) . The new species shares similar preopercular pore counts with Apterichtus jeffwilliamsi McCosker & Hibino, 2015 . However, it distinctly differs by possessing a fewer total vertebrae count (130–131 vs. 138–142 in A. jeffwilliamsi ); fewer preopercular pores (3 vs. 4); body colouration (golden yellowish to greenish body without spots vs. body pinkish white with numerous spots) ( McCosker & Hibino 2015).

The species differs from its Indian water congener A. nanjilnaduensis by having more supratemporal pores (9 vs. 5 in nanjilnaduensis ) and fewer preanal and total vertebrae (51–52 vs. 60–64 and 130–131 vs. 140–143) and fewer lateral-line pores before anus (56–59 vs. 58–61); further differs in having golden yellowish to greenish body (vs. golden reddish to pink body). Apterichtus kanniyakumari differs from its Indian ocean congener A. klazingai Hibino, Shibata & Kimura, 2014 in having more supratemporal pores (9 vs. 5 in A. klazingai ), vomerine teeth present (vs. absent) ( McCosker & Hibino 2015).

Further, the new species shares similar preanal and total vertebrae count with Apterichtus gracilis ( Kaup, 1856) , Apterichtus caecus ( Linnaeus, 1758) , Apterichtus orientalis Machida & Ohta, 1994 , Apterichtus succinus ( Hibino, McCosker & Kimura, 2016) (54-130). However, it can be easily distinguished from the above-mentioned species by having fewer preopercular pores (3 vs. 4) and more supratemporal pores (9 vs. 5) ( McCosker & Hibino 2015).

Apterichtus kanniyakumari differs from other congeners in having fewer preopercular pores, i.e., 3 vs. 4 in Apterichtus ansp ( Böhlke, 1968) , and Apterichtus hatookai Hibino, Shibata & Kimura, 2014 , and having more supratemporal pores: i.e., 9 vs. 5 in Apterichtus dunalailai McCosker & Hibino, 2015 , Apterichtus malabar McCosker & Hibino 2015 , Apterichtus nariculus McCosker & Hibino, 2015 , and Apterichtus soyoae Hibino, 2018 ; 5 or 6 in Apterichtus moseri ( Jordan & Snyder, 1901); 7 in Apterichtus monodi ( Roux, 1966) , and Apterichtus hatookai Hibino, Shibata & Kimura, 2014 ( McCosker & Hibino 2015; Hibino et al. 2016; Hibino 2018). Further, the new species differs from species such as Apterichtus anguiformis ( Peters, 1877) , Apterichtus australis McCosker & Randall, 2005 , A. dunalailai , Apterichtus equatorialis ( Myers & Wade, 1941) , A. flavicaudus , A. hatookai , Apterichtus kendalli ( Gilbert, 1891) , A. malabar , A. monodi , A. moseri , Apterichtus mysi McCosker & Hibino, 2015 , A. nariculus by having fewer total vertebrae (130–131 vs. 150–157 in A. anguiformis , 162–167 in A. australis , 160 in A. dunalailai , 132–146 in A. equatorialis , 154–166 in A. flavicaudus , 137–140 in A. hatookai , 137–145 in A. kendalli , 155–162 in A. malabar , 147–151 in A. monodi , 141–145 in A. moseri , 146–153 in A. mysi , 137 in A. nariculus ) ( McCosker & Hibino 2015).

Figures

FIGURE 1. Apterichtus kanniyakumari sp. nov. NBFGR/OPHAKAN, holotype, 365 mm TL, collected off Colachel, Arabian Sea.

FIGURE 2. Apterichtus kanniyakumari sp. nov. NBFGR/OPHAKAN, holotype, 365 mm TL, collected off Colachel, Arabian Sea. Head in fresh condition A) lateral view, B) ventral view (Scale bar = 5mm).

FIGURE 3. Preserved colouration Apterichtus kanniyakumari sp. nov. NBFGR/OPHAKAN, holotype, 365 mm TL, A) Lateral body, B) lateral view of head, C) dorsal view of head, D) ventral view of head.

FIGURE 4. Line drawing showing the lateral view of head pores of Apterichtus kanniyakumari sp. nov. M mandibular, PO preopercular, IO infraorbital, SO supraorbital, ST supratemporal.

FIGURE 5. A) Dentition of upper jaw, B) Dentition of lower jaw of Apterichtus kanniyakumari sp. nov. NBFGR/OPHAKAN, holotype, 365 mm TL.

FIGURE 6. The maximum likelihood tree of Apterichtus kanniyakumari sp. nov., and the related species were plotted with the model of BIC: TPM2+G4 with 1000 bootstrap replicates, based on mitochondrial CO1 gene sequences (bp). Each node represents branch support values.