Ariosoma kannani Kodeeswaran, Kathirvelpandian, Ray, Kumar, Mohapatra & Sarkar, 2024

Kodeeswaran, Paramasivam, Kathirvelpandian, Ayyathurai, Ray, Dipanjan, Mohapatra, Anil, Kumar, Thipramalai Thangappan Ajith, Raghunathan, Chelladurai & Kumar Sarkar, Uttam, 2024, Two new species of the congrid eel genus Ariosoma (Anguilliformes, Congridae, Bathymyrinae) from Indian waters, Zoosystematics and Evolution 100 (1), pp. 119-128 : 119

Ariosoma kannani Kodeeswaran, Kathirvelpandian, Ray, Kumar, Mohapatra & Sarkar sp. nov.

Figs 1b , 2b , 5

Type material.

Holotype. NBFGR/CONAKAN (171 mm TL), Rameshwaram Fish Landing Centre, Tamil Nadu, Gulf of Mannar, east coast of India, Bay of Bengal (9°16'N, 79°18'E), Coll. P. Kodeeswaran and A. Kathirvelpandian, 4 February 2022.

Paratype. EBRC/ZSI/F15710 (157 mm TL) taken with holotype, EBRC/ZSI/F15711 (201 mm TL), Shankarpur Fish Landing Centre, West Bengal, Coll. Dipanjan Ray, 10 November, 2021.

Diagnosis.

A small-sized slender eel species of Ariosoma distinguished from all other species by the following combination of the characters: dorsal-fin origin behind pectoral-fin insertion, pre-anal length 46.0-47.2% of TL, smaller eye, 20.7-21.1% HL, smaller interorbital distance, 8.9-10.7% HL, no distinct bands on head, pre-opercle whitish, teeth on jaw small, pointed, intermaxillary and vomerine teeth continuous, short vomerine tooth patch; SO canal with 6 pores; 3 pores on ST canal; pre-dorsal vertebrae 10 (10); pre-anal vertebrae 45 (45); total vertebrae 116 (118).

Description.

Body stout, anterior portion cylindrical, laterally compressed in tail region; caudal fin tip rounded; anus positioned at mid-point of body, pre-anal length 46.0-47.2% of TL; dorsal-fin origin behind pectoral-fin insertion, above tenth to eleventh lateral-line pores. Pectoral-fin developed, with a narrow base and round or blunt distally. Gill opening small, smaller than eye diameter, interbranchial width larger than gill opening and smaller than eye diameter.

Head moderately large 6.0 (5.5) in TL, snout short, anteriorly pointed in dorsal view, its length 1.1 times eye diameter, projecting beyond lower jaw; snout length shorter than lower jaw; fleshy portion of snout projecting anteriorly beyond the end of intermaxillary tooth patch; rictus positioned just behind middle length of eye. Tubular anterior nostril moderate in size at snout tip and posterior nostril relatively large elliptical pore, in front of mid-eye orbit diameter. Upper and lower jaw with reduced flange.

Lateral-line pores complete; first pore commences at level of supratemporal canal and terminates well before base of caudal fin; 10-11 pre-dorsal pores; 45-47 pre-anal pores and 110-111 total pores.

Head pores medium or small. SO canal pores 6; first pore (ethmoidal) smaller, on snout tip; second pore medium, just before anterior nostril; third pore enlarged, on dorsal surface of snout just behind anterior nostril; fourth pore moderate, behind posterior nostril; fifth pore smaller, at anterior interorbital space; sixth pore small at posterior interorbital space. IO canal pores 8 (4+4), first pore moderate, behind anterior nostril; second pore below posterior nostril; third pore below just before orbit eye-orbit margin; fourth pore at slightly before rictus, fifth pore behind rictus and 3 pores at infraorbital canal behind eye. POM pores 10; mandibular section with 7, pre-opercular section with 3 pores in a longitudinal row. ST pores 3, 1 median pore and 1 lateral pore on each side just behind median pore (Fig. 1b ).

Teeth on jaws small, pointed; continuous maxillary and intermaxillary teeth; intermaxillary and vomerine teeth continuous; vomerine teeth pointed anteriorly and blunt posteriorly, reach beyond mid-maxillary teeth row (Fig. 2b ).

Pre-dorsal vertebrae 10, pre-anal vertebrae 45-48; total vertebrae 116-118.

Colouration.

Dorsal body pale brownish; ventral half above anus whitish; dorsal fin margin black; anal fin clear; pre-opercle whitish; head brownish; interorbital region black; pectoral-fin translucent; ventral surface of lower jaw whitish without any black pigmentation (Fig. 5 ).

Distribution.

Indian Ocean: Gulf of Mannar, Bay of Bengal probably widespread in the east coast of India, but rare in catch.

Etymology.

The species was named after the late Prof. Dr. L. Kannan, Former Director, CAS in Marine Biology, Annamalai University and Former Vice Chancellor, Thiruvalluvar University for his contribution in Marine Science.

Comparison.

Ariosoma kannani is closely related to Ariosoma megalops from China, Taiwan and Vietnam waters in having the dorsal-fin origin behind the pectoral-fin insertion and similar vertebral counts, but the new species readily differs by having smaller interorbital distance (8.9-10.7% HL vs. 12.1-18.4% HL in A. megalops ) and smaller mean eye diameter (20.9% HL vs. 22.8-22.9% HL) and the new species show 10.8% genetic divergence from A. megalops from the Taiwan waters. The new species shares similar vertebral counts with Ariosoma scheelei , a widely distributed species in Indo-West Pacific, but A. kannani can be easily distinguished from A. scheelei by having fewer POM pores (10 vs. 12 in A. scheelei ) ( Smith et al. 2018) and shows 19.4% genetic differences. Further, A. kannani differs from all the Indian water congeners by having fewer total vertebrae (116-118 vs. 121-164 in others) and dorsal-fin origin behind pectoral-fin insertion ( Kodeeswaran et al. 2021, 2022a, 2022b, 2023; Ray et al. 2022).

Molecular analyses

Out of 548 bp studied, conserved and variable sites were found to be 348 bp, 200 bp long, respectively. Amongst variable sites, parsimony informative sites constitute 190 bp, wherein a singleton with 10 bp. The nucleotide composition was found to be A = 26.1%; T = 30%; C = 25.2%; G = 18.7. The transition and transversion bias (R) was documented using substitution patterns and rates were ascertained using the Kimura 2 Parameter model. The obtained R value of 7.48, clearly indicate the sequences of the species used for analyses are delineated in a proper manner. The R value supports the findings of genetic divergence values and phylogenetic tree analyses.

The Maximum Likelihood tree (Fig. 6 ), obtained using the sequences generated for the new species Ariosoma kannani along with other sister species, confirms the species identification as the new species forms a separate cluster and is closely related to the sequences of Ariosoma megalops from the Taiwan waters with 10.8% genetic divergence. Further, the new species A. kannani exhibits 16.3% distance with the sequences of Ariosoma kapala , 17.6% with A. bowersi , 18.9% with A. shiroanago , 19.2% with A. balearicum and 19.3% with A. anago .

Figures

Figure 1. Image showing the head pores and anterior lateral-line pores. a. Ariosoma gracile sp. nov., NBFGR / CONACOM, holotype (241 mm TL); b. Ariosoma kannani sp. nov., NBFGR / CONAKAN, holotype, (171 mm TL).

Figure 2. Dentition of upper jaw. a. Ariosoma gracile sp. nov., NBFGR / CONACOM, holotype (241 mm TL); b. Ariosoma kannani sp. nov., NBFGR / CONAKAN, holotype, (171 mm TL).

Figure 5. Ariosoma kannani sp. nov., NBFGR / CONAKAN, holotype, (171 mm TL). a. Lateral view; b. Lateral; c. Dorsal; d. Ventral view of anterior portion of head.

Figure 6. Maximum Likelihood phylogeny tree of the genus Ariosoma from analysis of cytochrome c oxidase subunit I gene, including new species, Ariosoma kannani collected from the south Indian coast, based on the IQ-Tree. The ML tree was plotted with the HKY + F + I + G 4 model using ModelFinder (Kalyaanamoorthy et al. 2017). Each node is labelled with a GenBank accession number and support values (bootstrap probability) are indicated along branches.