Stolephorus bengalensis (Dutt & Babu Rao, 1959)

Hata, Harutaka, Lavoue, Sebastien & Motomura, Hiroyuki, 2022, Description of three new species previously identified as Stolephorus bengalensis (Dutt & Babu Rao, 1959) or Stolephorus insularis Hardenberg, 1933 and a re-description of S. bengalensis (Chordata, Osteichthyes, Clupeiformes, Engraulidae), ZooKeys 1121, pp. 145-173 : 145

Stolephorus bengalensis (Dutt & Babu Rao, 1959)

[English name: Hardenberg’s Anchovy] Figs 2 , 3

Anchoviella baganensis bengalensis Dutt & Babu Rao, 1959: 160 [original locality: Waltair and Kakinada, Andhra Pradesh, east coast of India; type locality: Kilakarai, Gulf of Mannar, India, based on the neotype designated by Hata et al. (2019)].

Stolephorus baganensis macrops (lapsus memoriae for Stolephorus megalops ) (not of Delsman): Whitehead 1967 (in part): 18 (Bay of Bengal).

Stolephorus insularis (not of Delsman): Whitehead et al. 1988 (in part): 413 (northern part of Indian Ocean); Young et al. 1994: 222, fig. 7 (Wangkun and Fangliao, Taiwan); Wongratana et al. 1999 (in part): 1736 (northern part of Indian Ocean); Gangan et al. 2020: 562, fig. 5 (Kochi, Kerala State, India).

Stolephorus bengalensis : Hata et al. 2019 (in part): 24, fig. 12 (Pakistan and India; neotype designation).

Neotype.

USNM 276476, 45.8 mm SL, Kilakarai, Gulf of Mannar, India, 20 Feb 1964, J. W. Reintjes and P. S. B. R. James.

Non-type specimens.

46 specimens, 30.8-58.7 mm SL. India: BMNH 1969.5.30.34-45, 12 specimens, Chennai, Tamil Nadu State; OCF-P 10435, 4 specimens, 30.8-38.1 mm SL, estuary of Hooghly River, West Bengal State (purchased in fish market in Kolkata, West Bengal State); USNM 204227, 21 specimens, 42.7-51.8 mm SL, Sassan Docks, Mumbai, Maharashtra State. Pakistan: KAUM-I. 69286, 50.0 mm SL, KAUM-I. 69287, 58.7 mm SL, KAUM-I. 69288, 50.5 mm SL, KAUM-I. 69289, 54.4 mm SL, KAUM-I. 69290, 49.0 mm SL, KAUM-I. 69291, 53.1 mm SL, KAUM-I. 69292, 47.3 mm SL, KAUM-I. 69294, 58.6 mm, KAUM-I. 69295, 58.6 mm, West Wharf, Karachi.

Diagnosis.

A species of Stolephorus with the following combination of characters: 1UGR 16-19 (modally 18), 1LGR 23-27 (25), 1TGR 40-45 (44); 2UGR 11-15 (13), 2LGR 21-25 (23), 2TGR 33-39 (36); 3UGR 10-12 (11), 3LGR 13-15 (13), 3TGR 23-27 (24); 4UGR 7-9 (8), 4LGR 10-12 (11), 4TGR 17-21 (19); prepelvic scutes 5-7 (6); total vertebrae 40 or 41 (40); long maxilla, posterior tip just reaching or slightly short of posterior margin of opercle; predorsal scutes present; pelvic scute without spine; body scales deciduous; posterior border of pre-opercle concave, indented; paired dark patch on parietal area with little following pigmentation; distinct double pigment lines along dorsum posterior to dorsal fin; black spots below eye and on lower-jaw tip absent; anal-fin base long, 19.0-21.3% (20.2%) of SL; maximum orbit diameter 7.3-8.6% (8.1%) of SL; third dorsal-fin ray long, 18.5-19.9% (19.0%) of SL; pelvic fin rather long, 9.4-11.0% (10.2%) of SL, its posterior tip not reaching to vertical through dorsal-fin origin when depressed in specimens> 50 mm SL; distance between posterior ends of supramaxilla and maxilla 5.3-6.6% (5.8%) of SL.

Description.

Data for neotype presented first, followed by data for non-type specimens in parentheses (if different). Counts and measurements, expressed as percentages of SL or HL, given in Tables 2 and 3 . Body laterally compressed, elongate, deepest at dorsal-fin origin. Dorsal profile of head and body slightly convex from snout tip to dorsal-fin origin, gently lowering to uppermost point of caudal-fin base. Ventral profile of head and body slightly convex from lower jaw tip to pelvic-fin insertion, thereafter, slowly rising to lowermost point of caudal-fin base. Single spine-like scute just anterior to dorsal-fin origin. Abdomen somewhat rounded, covered with seven (four to seven) spine-like prepelvic scutes. Pelvic scute without spine. Postpelvic scutes absent. Anus just anterior to anal-fin origin. Snout tip rounded; snout length less than eye diameter. Mouth large, inferior, ventral to body axis, extending backwards beyond posterior margin of eye. Maxilla long, its posterior tip pointed, just reaching (or slightly short of) opercle posterior margin. Lower jaw slender. Single row of conical teeth on both jaws and palatine. Patch of fine conical teeth on pterygoid. Several distinct conical teeth on vomer. Several rows of conical teeth on upper edges of basihyal and basibranchial. Eye large, round, covered with adipose eyelid, positioned laterally on head dorsal to horizontal through pectoral-fin insertion, visible in dorsal view. Pupil round. Orbit elliptical. Nostrils close to each other, anterior to orbit. Posterior margin of pre-opercle concave, indented. Subopercle and opercle with smoothly rounded posterior margins. Gill membrane without serrations. Interorbital space flat, width less than eye diameter. Pseudobranchial filaments present, length of longest filament less than eye diameter. Gill rakers long, slender, rough, visible from side of head when mouth opened. Single row of asperities on anterior surface of gill rakers. Isthmus muscle long, reaching anteriorly to posterior margin of gill membranes. Urohyal hidden by isthmus muscle, not visible without dissection. Gill membrane on each side joined distally, most of isthmus muscle exposed, not covered by gill membrane. Scales on lateral surface of body thin, cycloid, deciduous, those on lateral body surface with several centrally continuous vertical grooves and several longitudinal striae anteriorly (Fig. 3 ). Head scales absent. Fins scaleless, except for broad triangular sheath of scales on caudal fin. Dorsal-fin origin posterior to vertical through base of last pelvic-fin ray, slightly posterior to middle of body. Dorsal and anal fins with three anteriormost rays unbranched. First dorsal- and anal-fin rays minute. Anteriormost three rays of both dorsal and anal fins closely spaced. Anal-fin origin just below base of tenth (ninth to eleventh) dorsal-fin ray. Posterior tip of depressed anal fin not reaching caudal-fin base. Uppermost pectoral-fin ray unbranched, inserted below body axis. Posterior tip of pectoral fin not reaching to pelvic fin insertion. Dorsal, ventral and posterior margins of pectoral fin nearly linear. Pelvic fin shorter than pectoral fin, insertion anterior to vertical through dorsal-fin origin. Posterior tip of depressed pelvic fin not reaching to vertical through dorsal-fin origin. Caudal fin forked, posterior tips pointed.

Colour of preserved specimens.

Body uniformly pale ivory. A pair of distinct dark patches on parietal region, with little pigmentation on occipital area. Double pigmented lines dorsally posterior to dorsal fin. A few melanophores scattered anteriorly on snout. No black spots below eye and on lower-jaw tip. Melanophores scattered along bases of dorsal and anal fins. All fins transparent, melanophores scattered along fin rays of caudal fin and anterior parts of dorsal and anal fins.

Distribution.

Stolephorus bengalensis is distributed in the northern Indian Ocean from Pakistan to the Bay of Bengal (Fig. 4 ). It is abundantly landed and marketed along the coast of the Bay of Bengal.

Morphological comparisons.

Stolephorus bengalensis has been considered conspecific with the three new species described herein, the four species being easily separable from all other congeners, except for Stolephorus acinaces , Stolephorus andhraensis Babu Rao, 1966, Stolephorus carpentariae (De Vis, 1882), Stolephorus hindustanensis Hata & Motomura, 2022, Stolephorus holodon (Boulenger, 1900), Stolephorus ronquilloi Wongratana, 1983 and Stolephorus tamilensis Gangan, Pavan-Kumar, Jahageerdar & Jaiswar, 2020, the former having a concavely indented pre-opercular margin and lacking a spine on the pelvic scute ( Whitehead et al. 1988; Wongratana et al. 1999; Kimura et al. 2009; Hata and Motomura 2018a, b, c, d, e, 2021a, b, c, 2022; Hata et al. 2019, 2020a, b, 2021; Gangan et al. 2020). However, the former four species are distinguished from the other seven by having a predorsal scute (vs. absent in the latter) and double dark lines on the dorsum posterior to the dorsal fin (vs. no lines on the dorsum, except in S. hindustanensis and S. ronquilloi ). Moreover, S. carpentariae also differs from S. bengalensis and the three new species in having 19 or 20 branched anal-fin rays [16-18 (rarely 19 or 20) in the remaining five species] and the anal-fin origin located below the origin of the second to sixth dorsal-fin ray (vs. eighth to eleventh) ( Whitehead et al. 1988; Wongratana et al. 1999; Gangan et al. 2020; Hata et al. 2020b). Stolephorus bengalensis , S. diabolus sp. nov., S. eclipsis sp. nov. and S. eldorado sp. nov. resemble Stolephorus baganensis Delsman, 1931, Stolephorus dubiosus Wongratana, 1983 and Stolephorus tri (Bleeker, 1852) in having a predorsal scute and double pigment lines on the dorsum behind the dorsal fin, but differ in having deciduous body scales (vs. body scales not deciduous) and lacking a spine on the pelvic scute (pelvic scute with a hard posteriorly projecting spine) ( Whitehead et al. 1988; Wongratana et al. 1999; Hata et al. 2019). Comparisons of S. bengalensis with S. diabolus sp. nov., S. eclipsis sp. nov. and S. eldorado sp. nov. are given in “Comparisons” under each new species.

Molecular comparisons.

Stolephorus bengalensis , S. diabolus sp. nov. and S. eldorado sp. nov. were divergent from each other by at least 3.5% COI-based mean uncorrected genetic distance (min-max = 3.5-7.7%) (Fig. 5 ). In contrast, each species was genetically uniform, with intraspecific differentiation not exceeding 1% (note: Stolephorus sp. represented by a single specimen - see below), forming clear intraspecific versus interspecific genetic gaps. The ML phylogenetic tree using COI and cytochrome b markers (Fig. 5 ) was fully resolved, with interspecific relationships supported by bootstrap values above 80%. Each species formed a well-supported monophyletic group, in agreement with their genetic distinction, thereby confirming their taxonomic status, which was further supported by the morphological observations. The COI sequence of an unidentified larva collected from the Segara Anakan Lagoon, Central Java ( Nuryanto et al. 2017), indicated either a range extension of S. eclipsis sp. nov. or the presence of an unidentified species of Stolephorus , related to S. bengalensis .

Figures

Figure 2. A lateral B dorsal and C ventral views of neotype of Stolephorus bengalensis (USNM 276476, 45.6 mm SL, Gulf of Mannar, India). Scale bars indicate 2 mm.

Figure 3. Stained scale removed from right side of mid-body (above anal fin) of Stolephorus bengalensis, BMNH 1969.5.30.34 - 45, 47.8 mm SL, Chennai, India (left-right inverted; scale bar indicates 0.5 mm).

Figure 4. Map of the northern part of the Indo-West Pacific region showing distributional records of Stolephorus bengalensis (red circles), S. diabolus (yellow squares) sp. nov., S. eclipsis (green diamond) sp. nov. and S. eldorado (blue triangles) sp. nov., based on specimens examined in this study. Land masses outlined with black lines.

Figure 5. Maximum-likelihood phylogenetic tree of four species of Stolephorus related to S. bengalensis, based on the cytochrome b and cytochrome oxidase I genes (total: 1,788 base pairs) of 31 specimens, each species forming a monophyletic group. Each specimen identified by Museum Registration Number or GenBank number (see text and Table 1 for details). Type status (either holotype or paratype), specimen code, gene used (mt or COI) and sequence origin (GB) are indicated in brackets where necessary. Tree rooted by a specimen of Stolephorus andhraensis. Branch lengths proportional to number of substitutions. Bootstrap proportions indicated at nodes.