Ariosoma bengalense sp. nov.

Proposed common name: Bengal conger

(Figures1–5, Table 1)

Holotype. EBRC / ZSI / F 12898, 304 mm TL, Petua Ghat, West Bengal, India, 29.11.2019. Paratype. EBRC / ZSI / F 12899, 216 mm TL, same data as holotype

Diagnosis. A medium sized conger eel with dorsal-fin origin above the gill-opening margin and above the 9 th lateral-line pore, comparatively large circular eyes, mouth cleft below middle of eye, no supratemporal pore, lateralline pores 135–136. Teeth multiserial, moderately large, blunt and granular. Two pale bands cross dorsal surface of head, the first located at the posterior edge of eyes and second on the supratemporal canal. Teeth unequal in size, bluntly pointed teeth interspersed with granular ones on maxilla and vomer. Vomerine tooth patch extends posteriorly to the level of anterior margin of orbit. Vertebral count, 9–10 predorsal; 46–49 preanal; 146–149 total.

Description. Morphometric measurements in proportion with TL and HL of the holotype are documented. Data for paratype in parentheses. Body stout and elongate, compressed at tail region, caudal tip stiff. Anus located anterior to midpoint of body, preanal length 41.1% (40.7%) TL. Anal-fin origin just behind anus; anal opening small and oval-shaped. Head length 18.3% (16.7%) TL. Dorsal-fin origin of both holotype and paratype located above the 9 th lateral-line pore and above gill opening margin. Pectoral fin well-developed, tip pointed, with 16 (15) rays, 41.2% (31.9%) HL. Gill opening moderately large, greater than eye diameter. Anterior nostril tubular at tip of upper lip. Posterior nostril elliptical in front of eye at lower level of pupil but not in contact. Eyes relatively large, almost circular, 8.6 (7.3) in HL. Rictus below middle of eye. Snout pointed. Upper jaw 1.2 (1.5) times longer than lower jaw. Head pores small with some slightly enlarged pores. Supraorbital canal with 4 pores; first small ethmoidal pore present at ventral tip of snout, second small pore at immediate above of anterior nostril, third slightly enlarged pore just behind anterior nostril, fourth enlarged pore closer to anterior edge posterior nostril, on level with upper eye. Infraorbital canal with 7 (4+3) pores, first between the nostrils, second just behind posterior nostril, third on mid-eye level, fourth just behind the rictus; three pores present just behind eye. Mandibular pores 9; preopercular pores 3; supratemporal pores absent; predorsal lateral-line pores 9 (Fig.2), preanal lateral-line pores 46–49, total lateral-line pores 135–136.

Each series of teeth moderately large, blunt and granular. Maxilla and inter maxillary teeth are continuous (Fig 3). Intermaxillary teeth with 3–4 rows of teeth mixed with both blunted and granular teeth. Maxilla with 1–4 rows of teeth mixed with blunt and granular teeth.. Teeth unequal in size; and blunted teeth are variable in size. Vomer with 1–3 rows in patch that extends posteriorly to mid–eye with blunt teeth from snout tip to middle of vomerine patch and granular teeth towards posterior end; maxillary and intermaxillary teeth patches continuous (Fig.3), without gap or suture between patches. Myorhabdoi absent. Vertebrae: 9–10 predorsal; 46–49 preanal; 61–66 precaudal; 146–149 total.

Colouration (in preservative). Body brown, dorsal and anal fins with thin black margins; eye pupil black; two pale bands cross dorsally on head, the first located at posterior end of orbit and second on the supratemporal region. Pectoral fin pale.

Distribution. This species is currently known from the northern part of the Bay of Bengal (West Bengal), India, 197 km away from the Deshpran fishing harbor, at a depth of 168 m (21047.752’N, 87052.869’E), within the Exclusive Economic Zone of India.

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TABLE 1. (Continued)

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TABLE 1. (Continued)

Note: The upper jaw measurement of A. gnanadossi (Holotype), A. indicum (Non types) and A. majus (from Indian waters) were done by authors.

Etymology. The new species is named after the type locality (Bay of Bengal).

Comparison. Among all the 35 species reported worldwide, seven Ariosoma species are reported from India to date: A. anago, A. dolichopterum, A. gnanadossi, A. indicum, A. majus, A. maurostigma and A. melanospilos (Kodeeswaran et al. 2021; Roy et al. 2021; Kodeeswaran et al. 2022a, b). However, records of A. anago and A. dolichopterum need to be revisited as the identity of both the species from Indian waters is doubtful. The new species differs significantly from the remaining five species. The new species possesses significantly less preanal vertebrae counts than A. anago (46–49 vs. 54–56) (Smith et al. 2018). The new species differs from A. dolichopterum by substantially higher total vertebrae count (146–149 vs. 127–134) (Karmovskaya, 2015). In the new species the snout length is longer than eye diameter, but in A. gnanadossi, the snout length is almost equal to the eye diameter (11.7–13.7% vs. 18.8–23.6 HL). In addition, in the new species the interorbital space is lesser than A. gnanadossi (7.5–9.8% vs. 18.2% HL) and the trunk length is longer than A. gnanadossi (23.6–24.2% vs. 22.3% TL) (Talwar & Mukherjee 1977, Kodeeswaran et al. 2021). The new species differs from A. indicum by the absence of supratemporal pores (3 in A. indicum) also the new species has comparatively smaller eye diameter than A. indicum (11.7–13.7% vs. 15.3–17.6% in HL in A. indicum) (Kodeeswaran et al. 2022b). The new species differs from A. majus by the absence of supratemporal pores (vs. 3 in A. majus), dorsal-fin origin (dorsal-fin origin above the gill opening in the new species vs. well before gill opening in A. majus) and fewer preanal vertebrae (46–49 vs. 51–55 in A. majus) (Smith et al. 2018, Roy et al. 2021). The new species differs from Ariosoma maurostigma by less preanal length in comparison to percentage of total length 40.7–41.1% vs. 44.0–48.8% in TL (Kodeeswaran et al. 2022a). The new species lacks black coloration near eye and mid dorsal temporal region, whereas Ariosoma melanospilos has two black patches at the posterior margin of the eye and two black spots on each side of mid-dorsal temporal region, for which the new spcies can be easily differentiated from A. melanospilos (Kodeeswaran et al. 2021). Additionally, the preanal vertebrae are fewer in the new species in comparison to A. melanospilos (46–49 vs. 55–56). From remaining 28 species of world seven species: A. balearicum (Delaroche,1809), A. emmae Smith & Ho, 2018, A. gilberti (Ogilby, 1898), A. megalops (Fowler, 1938) A. obud Herre, 1923, A. scheelei (Strömman, 1896) and A. sokotranum Karmovskaya, 1991 have significantly fewer vertebrae than the new species (114–141 vs. 146–149 in the new species) (Castle 1968, Karmovskaya 1991, Karmovskaya 2018, Smith et al. 2018). Seven species, namely A. coquettei Smith & Kanazawa, 1977, A. fasciatum, A. multivertebratum Karmovskaya, 2004, A. nigrimanum, A. sereti Karmovskaya, 2004 A. shiroanago (Asano, 1958) and A. selenops, Reid, 1934, have significantly more vertebrae than the new species (154–172 vs. 146–149) (Smith et al. 2018, Smith & Kanazawa 1977, Karmovskaya, 2004, Castle, 1968). Two species of Ariosoma, namely A. anale (Poey, 1860) A. meeki (Jordan & Snyder, 1900), possess significantly more preanal vertebrae than the new species (52–66 vs. 46–49 in the new species), (Karmovskaya 2018, Smith et al. 2018).

Among the remaining 12 species, six species: A. anagoides (Bleeker, 1853), A. bauchotae (Karrer, 1983), A. howensis (McCulloch & Waite, 1916) A. kapala (Castle, 1990), A. mauritianum (Pappenheim, 1914) and A. sazonovi Karmovskaya, 2004, have an overlapping vertebral count with new species. Ariosoma anagoides, A. howensis and A. sazonovi differ from new species in having three supratemporal pores (vs. absent in the new species) (Karmovskaya 2004, Karmovskaya 2018). Ariosoma anagoides possesses more preanal lateral line pores than the new species (54 vs. 46–49). Ariosoma bauchotae differs from the new species in having larger eyes (17.0–18.6% vs. 11.7–13.7% HL) (Karrer 1983). Ariosoma kapala has a lower lateral-line pore count (139) than the new species (135–136), higher precaudal vertebrae count 74 vs. 61–66 in new species and has supratemporal pores (absent in the new species) (Castle 1990).

The new species also differs significantly from the remaining eight species. Ariosoma bowersi (Jenkins, 1903) can be distinguished by having a larger eye diameter (4.0 vs. 7.3–8.6 in HL), more preanal length (1.25 vs. 2.4–2.5 in TL), small and sharp teeth (Jenkins 1903) vs. conical and granular teeth in the new species. Ariosoma hemiaspidus (Wade, 1946) possesses significantly fewer lateral-line pores (116 vs. 135–136 in new species) and more preanal lateral-line pores (51 vs. 46–49) (Wade 1946). Ariosoma mellissii (Günther, 1870) has a short snout compared to eye diameter, equal in length to the eye, but in the new species, snout length is 1.42–2.02 longer than the eye diameter. In addition, the eye diameter of Ariosoma mellissii is 0.2 times of head vs. 0.12–0.13 times in the new species and A. mellissii has villiform teeth on jaws vs. blunt and granular teeth in new species (Günther 1870). Ariosoma ophidiophthalmus Karmovskaya, 1991 has more preanal lateral-line pores (54–57) than the new species (46–49); teeth arranged in 7–8 rows on both jaws (vs. 1–4 rows on jaws) and 6–7 rows of vomerine teeth (vs. 1–3 rows in the new species) (Karmovskaya 1991). Ariosoma opistophthalmum (Ranzani, 1839) differs from new species in having a dark brown pectoral fin with black edge (vs. pale pectoral fin without black edge) (Ranzani 1839). Ariosoma sanzoi is described from leptocephali with myomere count of 123 (D’Ancona 1928), far fewer than 146–149 vertebrae of the new species. Ariosoma vomerina Myers & Wade, 1941 differs from the new species in having a very small vomerine tooth patch and the maxillary teeth having similar shape and size to mandibular teeth vs. comparatively long vomerine tooth patch and larger maxillary teeth than mandibular teeth (Myers & Wade 1941).

Comparative material: Ariosoma majus — 2 specimens (EBRC / ZSI /F 11528, 225– 291 mm TL), Ariosoma gnanadossi — Holotype (ZSI F 7146 / 2, 283 mm TL), A. maurostigma – Paratypes — 4 specimens (EBRC / ZSI /F12905, 206– 273 mm) and A. indicum — Paratypes: 2 specimens (EBRC / ZSI /F13597) and 7 specimens non types ((EBRC / ZSI /F13604)