Eleotris sahanaensis, Mennesson & Keith, 2020

Mennesson, Marion I. & Keith, Philippe, 2020, Eleotris (Teleostei: Eleotridae) of the Indian Ocean: an overview with the description of three new species, Cybium 44 (3), pp. 185-203 : 196-197

Eleotris sahanaensis sp. nov. Mennesson, Keith & Feunteun

( Figs 1B , 2, 5; Tabs III-V)

Material examined

One male and one juvenile collected from Madagascar with a size range of 26-44 mm SL .

Holotype. – MNHN-IC-2020-0078, male (44 mm SL), Sahana River , Madagascar; July 2008; Diamsoi coll.; tag 13003.

Paratype. – MNHN-IC-2020-0077, juv. (26 mm SL), Andrepona River , Madagascar; 4 Jul. 2008; Diamsoi coll.; tag 7278 .

Diagnosis

The species is distinguished by: second and fourth suborbital free neuromast rows on cheek extending ventrally past horizontal row d (‘2.4’ pattern), row os not connected with row oi at ventro-posterior margin of operculum (‘open’ pattern); 15 pectoral fin rays; no teeth on vomer; 54-55 scales in lateral series and 29-30 scales in predorsal series.

Description

Scale counts in Eleotris sahanaensis sp. nov. and related species are given in table III, ray counts in table IV and morphometrics in table V . Below, the holotype counts are given first followed in brackets, if different, by the paratype counts.

The body is elongated. The body depth at anus is 22 (16% SL) and the caudal peduncle depth is 12 (11% SL). Predorsal length 47 (46% SL) and preanal length 63 (61% SL).

The head 32 (30% SL) is broad and depressed, the snout is pointed. Eyes high on head. The mouth is quite large, as jaw length 11 (9% SL), and oblique, the posterior margin of upper jaw reaches the vertical through the two thirds of the eye. Upper and lower jaws with multiple rows of small inwardly curved teeth.

Dorsal fins VI-I,8-9; D1 separate from and smaller than D2; spines not elongated. Anal fin I,8-9 and directly opposite to second dorsal fin. Pelvic fins separate, I,5. Pectoral fins 15. Caudal fin pointed with 15 branched rays.

Cycloid scales on top of head, nape, cheek, operculum, pectoral fin base, prepelvic region, and abdomen. Ctenoid scales covering flanks. No lateral line canals. 55 (54) scales in lateral series, 29 (30) in predorsal series, 15 (14) in transverse back series, 19 (20) in transverse forward series and 10 in zigzag series.

A downward pointing spine at the posterior margin of the preoperculum is covered with skin. Gill opening is moderately broad, extending to below the preoperculum. Tubular anterior nares overhanging half upper lip, posterior nares open pits.

Cephalic lateralis: Adults with five transverse suborbital free neuromast rows of which second and fourth suborbital free neuromast rows on cheek extend ventrally past horizontal row d (‘2.4’ pattern); row os not connected with row oi at ventro-posterior margin of operculum (‘open pattern’) ( Fig. 1B ).

Urogenital papilla elongated and tapered in male.

Colour in life Unknown.

Colour in preservation ( Fig. 5 )

Head and preoperculum greyish, finely spotted and with 3-4 oblique brown lines from the eye to the edge of operculum. Back brown, flanks light brown with numerous dots more or less aligned from the operculum to the hypural. A big blackish area at the anterior part of the flanks, below the medial part. Abdomen and gular region whitish to yellowish and finely spotted. A black dot at the base of the pectoral fins. Anal and second dorsal fins with 3-4 dark horizontal bands alternating with 3 small white ones. Caudal fin greyish, with 2-3 small spots anteriorly. Pelvic fins whitish.

Comparison

Eleotris sahanaensis differs from the other species sequenced that occur in the area studied by having a high % of divergence in COI gene [79 bp alignment] (3.8-10.1%).

Within the pattern ‘ 2.4 ’, E. sahanaensis differs from E. acanthopoma in having 15 pectoral fin rays versus 16-17, 10 scales in zigzag series versus 11-14, and 29-30 scales in predorsal series versus 30-42. It differs from E. vomerodentata by the absence of teeth in the vomer versus presence. It differs from E. pellegrini by a smaller head length (30-32 versus 31-37% SL) and fewer scales in zigzag series (10 versus 10-12).

Distribution

Currently known only from Madagascar. It was found in sympatry with E. pellegrini and E. diamsoi (this paper).

Ecology Unknown.

Etymology

The new species is named after the Sahana River, type locality, where many species of Eleotris were found.

Figures

Figure 1. – The five different cephalic neuromast patterns in Eleotris.

Figure 5. – Eleotris sahanaensis n. sp., Sahana River, Madagascar (tag 13003) (© M.I. Mennesson).