Ariosoma gracile Kodeeswaran, Kathirvelpandian, Mohapatra, Kumar & 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

publication ID	https://dx.doi.org/10.3897/zse.100.116611
publication LSID	lsid:zoobank.org:pub:FD307F80-4B3E-41E1-9283-E5C93C17C399
persistent identifier	https://treatment.plazi.org/id/757F2921-E865-4B92-B363-F7C90DB2E241
taxon LSID	lsid:zoobank.org:act:757F2921-E865-4B92-B363-F7C90DB2E241
treatment provided by	Zoosystematics and Evolution by Pensoft
scientific name	Ariosoma gracile Kodeeswaran, Kathirvelpandian, Mohapatra, Kumar & Sarkar
status	sp. nov.

Treatment

Ariosoma gracile Kodeeswaran, Kathirvelpandian, Mohapatra, Kumar & Sarkar sp. nov.

Figs 1a View Figure 1 , 2a View Figure 2 , 3 View Figure 3 , 4 View Figure 4

Type material.

Holotype. NBFGR/CONACOM, 241 mm TL, collected from deep-sea trawl by-catch, Kalamukku Fishing Harbour, off Kerala coast, Arabian Sea, 9°59'N, 76°14'E, P. Kodeeswaran, 19 February 2021.

Paratypes. NBFGR/CONACOM.1-2, (2:197-199 mm TL) and EBRC/ZSI/F15709 (2: 206-221 mm TL) taken with holotype.

Diagnosis.

A medium-sized slender eel species of Ariosoma distinguished from all other species by the following combination of characters: position of anus well-before middle of total length, pre-anal length 43.7% (41.3-44.7%) of TL; tail longer, 55.3-58.7% TL; dorsal-fin above pectoral-fin base; no dark or whitish bands on dorsal surface of head, ventral extremities and mid-portion of lower jaw with minute dark pigmentation patch; short vomerine teeth patch with three or four rows of pointed teeth in anterior portion, intermaxillary teeth patch curved, slightly upturned at anterior end, clearly visible when mouth closed, separated from vomerine and maxillary teeth by a definite gap; SO canal with 4 pores; 0 or 3 pores on ST canal; pre-dorsal vertebrae 9 (9); pre-anal vertebrae 48 (49-54); total vertebrae 141 (140-142).

Description

(dimensions in mm). Morphometric and meristic data are provided in Table 1 View Table 1 . HL 5.9 (5.5-5.7) in TL; pre-anal length 2.3 (2.2); pre-dorsal length 5.7 (5.6-5.8); trunk length 4.9 (4.1-4.6); tail length 1.7 (1.8); and depth at gill opening 18.2 (18.1-23.4). Snout length 5.1 (4.7-5.3) in HL; eye diameter 5.8 (5.4-6.4); interorbital width 9.9 (8.5-14.9); upper jaw 3.4 (3.1-3.6); gill opening width 5.8 (5.6-9.6); interbranchial width 8.8 (8.0-11.3); and pectoral fin 2.9 (2.7-3.7).

Body slender, cylindrical anterior portion, followed by more laterally compressed caudal portion; tip of caudal fin stiff and blunt or conical; anus positioned well-before mid-point of total length, pre-anal length 43.7% (41.3-44.7%) of TL; dorsal-fin origin above pectoral-fin base, above ninth lateral-line pores, confluent with caudal and anal fin. Origin of anal fin just after anus. Pectoral fin developed, with narrow base and pointed distally. Gill opening medium, slightly larger or equal to eye diameter, its upper origin reaching nearly upper half of pectoral-fin base; interbranchial width smaller than gill opening and eye diameter.

Head fairly large 5.9 (5.5-5.7) in TL, snout very short, anteriorly pointed in dorsal view, its length 1.1 (1.1-1.2) times eye diameter, projecting beyond lower jaw; length of snout relatively shorter than lower jaw; fleshy portion of snout projecting anteriorly beyond the end of intermaxillary tooth patch; rictus positioned just before middle length of eye. Fairly large tubular anterior nostril at tip of snout and relatively large elliptical pore of posterior nostril in front of mid-eye orbit diameter. Upper and lower jaw with slightly reduced flange. Tongue short and narrow; anterior portion free from mouth with conical or blunt tip.

Lateral-line pores complete; first pore commences moderately at level of supratemporal canal and terminating well before caudal-fin base; 9 (9) pre-dorsal pores; 43 (43-46) pre-anal pores and 132 (132-138) total pores.

Head pores moderate, few pores rather small. SO canal with 4 pores; first (ethmoidal) relatively small, on ventral side of snout tip; second pore medium-sized, in front of anterior nostril; third pore enlarged, on dorsal surface of snout just behind anterior nostril; fourth pore circular and enlarged, no pores in interorbital portion. IO canal with 8 (4+4) pores, first pore large, behind anterior nostril; second pore below posterior end of posterior nostril; third pore below anterior eye-orbit margin; fourth pore at above or slightly before rictus, below mid-eye; fifth pore behind rictus, at posterior margin of eye and 3 pores at infraorbital canal behind eye. POM pores 10; 7 in mandibular section, 6 before rictus and 1 behind rictus; pre-opercular section with 3 pores in a longitudinal row. Small-sized ST pores 0 or 3, (holotype and one paratype does not possess ST pores, 2 specimens with 3 pores and one specimen with 2 pores) (Fig. 3 View Figure 3 ).

Pre-dorsal vertebrae 9 (9); pre-anal vertebrae 48 (49-54); total vertebrae 141 (140-142).

Teeth larger, conical or pointed (no blunt teeth) (Fig. 2a View Figure 2 ). Curved intermaxillary teeth patch with three or four transverse rows, clearly visible when mouth closed, anterior portion fairly upturned, separated from vomerine and maxillary teeth by a definite gap. Maxillary and mandibular teeth continuous in bands; anterior part of maxillary teeth narrow with three rows, middle portion with two rows, innermost and outermost teeth pointed or conical, followed by uniserial pointed teeth posteriorly. Mandibular teeth wider anteriorly and narrower posteriorly. Vomerine teeth form a short patch, reaching in front of posterior nostril, three or four rows with pointed teeth in anterior portion, followed by four irregular triserial pointed teeth and two conical teeth in a series posteriorly.

Colour

(in fresh specimens). Body often bicolour, dark brownish to paler, upper half almost darker and paler ventrally; very minute dark pigmentations irregularly spread over body. Dorsal and anal fin creamy-white with thin black margin; caudal fin dull white with black upper and lower margins (Fig. 1 View Figure 1 ). Head same as body, dorsal surface of head without any dark or whitish bands, extremities of lower jaw under surface and mid-portion with minute dark pigmentation patch (Fig. 4b, c View Figure 4 ). Eyes bright with dark pupil, surrounded by thick pale golden-yellowish ring. Pectoral fin goldish-yellow (Fig. 4a View Figure 4 ). Colour in formalin slightly darker than fresh material or almost beige; pectoral fin translucent. Dark pigmentation patch remains on the ventral head.

Distribution.

Known from five specimens collected from trawl by-catches landings at Kalamukku Fishing Harbour, off Kerala, south-western Indian coast, Arabian Sea, western Indian Ocean.

Etymology.

From the Latin word, ' gracilis - gracile ' meaning slender, which denotes the slender-bodied eel.

Comparisons.

Ariosoma gracile differs from all the congeners but shares similar morphological characters and overlapping pre-anal vertebrae counts with Ariosoma dolichopterum Karmovskaya, 2015 from the South China Sea, off Vietnam and Taiwan and Ariosoma emmae Smith & Ho, 2018 from Taiwan waters. Ariosoma gracile differs from these congeners by having: 132-135 total pores (vs. 121-129 in A. dolichopterum , 123-126 in A. emmae ); 43-46 pre-anal pores (vs. 47-51 in A. dolichopterum , 50-53 in A. emmae ); 9 pre-dorsal pores (vs. 5-9 in A. dolichopterum , 4-6 in A. emmae ); more total vertebrae (140-142 vs. 129-134 in A. dolichopterum , 127-133 in A. emmae ); trunk 38.5-42.6% TL (vs. 26.6-29.8% TL in A. dolichopterum , 28.9-32.7% TL in A. emmae ); short vomerine tooth patch (vs. long in A. dolichopterum and A. emmae ) ( Karmovskaya 2015; Smith et al. 2018).

Ariosoma gracile differs from the Indian water congeners, such as Ariosoma gnanadossi Talwar & Mukherjee, 1977, Ariosoma melanospilos Kodeeswaran, Jayakumar, Akash, Kumar & Lal, 2021, Ariosoma albimaculatum Kodeeswaran, Dhas, Kumar & Lal, 2022 and Ariosoma sp. nov. Kodeeswaran et al. (in press) in having fewer total vertebrae (140-142 vs. 161-164 in A. albimaculatum ; 146 in A. gnanadossi ; 144-153 in A. melanospilos ; 162-163 in Ariosoma sp. nov.); fewer total pores (132-135 vs. 145 in A. gnanadossi ; 136-144 in A. melanospilos ; 148-155 in Ariosoma sp. nov.). The new species shares similar vertebral counts with Ariosoma maurostigma Kodeeswaran, Mohapatra, Dhinakaran, Kumar & Lal, 2022, but readily differs from the latter by the absence of a dark spot on posterior-dorsal margins of eye orbit (vs. present in A. maurostigma ); tail longer (55.3-58.7% TL vs. 47.8-54.6% TL); shorter pre-anal length (41.3-44.7% TL vs. 44.0-48.8% SL); fewer SO pores (4 vs. 6). Further, the new species differs from Ariosoma majus (Asano, 1958) in having more pre-dorsal pores (9 vs. 6-7 in A. majus ); fewer pre-anal pores (43-46 vs. 50-53); fewer total pores (132-135 vs. 139-142); smaller depth at gill opening (4.3-5.5% TL vs. 6.7-7.3% TL); fewer SO pores (4 vs. 6). Further, the new species shares overlapping vertebral counts with newly-described sympatric species Ariosoma indicum Kodeeswaran, Kathirvelpandian, Acharya, Mohanty, Mohapatra, Kumar & Lal, 2022, but the new species differs from the latter in having shorter pectoral fin (26.8-36.9% HL vs. 37.5-46.7% HL in A. indicum ); smaller interorbital width (6.7-11.8% HL vs. 11.8-15.7% HL); fewer SO pores (4 vs. 5); ST pores (0 vs. 3); pectoral fin grey (vs. blackish or bicoloured).