Stolephorus diabolus, Hata & Lavoué & Motomura, 2022

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 diabolus sp. nov.

[New English name: Demon Anchovy] Figs 1C , 6

Stolephorus bengalensis (not of Dutt and Babu Rao): Hata et al. 2022: (in part) 34 (Singapore).

Holotype.

IPMB-I 13.00001, 49.7 mm SL, Teluk Bahang, Penang, Malaysia.

Paratypes.

14 specimens, 28.5-43.7 mm SL. USMFC 82-0017, 43.7 mm SL, collected with the holotype; USMFC 82-0057, 4 specimens, 40.1-41.1 mm SL, estuary of Merbok River, Jeti Semeling, Malaysia; ZUMT 62056, 5 specimens, 28.5-38.4 mm SL, KAUM-I. 163702, 36.3 mm SL, KAUM-I. 163703, 36.4 mm SL, NSMT-P 143554, 36.4 mm SL, NSMT-P 143555, 36.6 mm SL, Singapore.

Diagnosis.

A species of Stolephorus with the following combination of characters: 1UGR 14-16 (modally 16), 1LGR 20-23 (22), 1TGR 35-38 (38); 2UGR 10 or 11 (11), 2LGR 19 or 20 (20), 2TGR 30 or 31 (31); 3UGR 8 or 9 (9), 3LGR 11 or 12 (12), 3TGR 20 or 21 (21); 4UGR 6 or 7 (7), 4LGR 9 or 10 (9), 4TGR 15-17 (17); prepelvic scutes 5-7 (6); total vertebrae 39; long maxilla, posterior tip just reaching or slightly short of posterior margin of opercle; predorsal scute 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, 19.8-22.3% (mean 20.7%) of SL; maximum orbit diameter 8.1-8.7% (8.3%) of SL; third dorsal-fin ray short, 17.0-18.5% (18.0%) of SL; pelvic fin rather long, 9.6-11.3% (10.0%) of SL, its posterior tip not reaching to vertical through dorsal-fin origin when depressed in specimens> 40 mm SL; distance between posterior ends of supramaxilla and maxilla 5.7-6.4% (6.1%) of SL.

Description.

Data for holotype presented first, followed by data for paratypes in parentheses (if different). Counts and measurements, expressed as percentages of SL or HL, given in Tables 5 and 6 . 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. Scutes on ventrum broken in holotype (five to seven spine-like prepelvic scutes on ventrum in paratypes). 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 broken in holotype (posterior pointed, just reaching or slightly short of opercle posterior margin in paratypes). 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. Body scales deciduous, completely lacking on specimens, except for prepelvic scutes. 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 eighth (eighth 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 (reaching to vertical through first to sixth dorsal-fin ray origin in some paratypes smaller than 40 mm SL). Caudal fin forked, posterior tips pointed.

Colour of preserved specimens.

Body uniformly pale white. A pair of distinct dark patches on parietal region, with little pigmentation on occipital area. No black spots below eye and on lower-jaw tip. Melanophores scattered on posterior margins of scale pockets on dorsum. Double pigmented lines dorsally posterior to dorsal fin. 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 diabolus sp. nov. is currently known only from the western coast of the Peninsular Malaysia (Merbok River Estuary and Penang) and Singapore (Fig. 4 ).

Etymology.

The specific name " diabolus " is derived from Latin meaning “demon”, in reference to the hard spine on the dorsum of the species.

Comparisons.

The new species is distinguished from S. bengalensis , S. eclipsis and S. eldorado by lower gill raker counts: 1TGR, 35-38 in S. diabolus (vs. 40 or more in the other three species); 2TGR, 30 or 31 in S. diabolus [vs. 33 or more (rarely 30 or 31 in S. eldorado )]; 3TGR, 20 or 21 in S. diabolus [vs. 22 or more in the other three species (rarely 21 in S. eldorado )]; and 4TGR, 15-17 in S. diabolus (vs. 17 or more) (Fig. 7 ). Moreover, S. diabolus has a shorter orbit diameter than S. eldorado [maximum orbit diameter 8.1-8.7% (mean 8.3%) of SL in S. diabolus vs. 8.2-9.9% (8.9%) in S. eldorado ; Fig. 8A ]. Furthermore, S. diabolus is distinguished from S. bengalensis by having a shorter third dorsal-fin ray [17.0-18.5% (mean 18.0%) of SL in S. diabolus vs. 18.5-19.9% (19.0%) in S. bengalensis (Fig. 8B )] and lower total vertebral numbers [39 vs. 40 or 41 (modally 40) (Table 4 )]. Detailed comparisons of S. diabolus with S. eclipsis and S. eldorado are given in “Comparisons” under each species.

Figures

Figure 1. Diagnostic characters of species previously identified as Stolephorus bengalensis A lateral view of whole body B dorsal-fin origin (triangle indicates predorsal scute, located just anterior to dorsal-fin origin) C dorsal view of dorsum behind dorsal fin (triangle indicates paired dark lines) D lateral surface of head (triangle indicates posterior tip of maxilla, posteriorly well beyond posterior margin of pre-opercle) E pre-opercle with concave posterior margin (supramaxilla removed) and F ventral view of pelvic fin (triangle indicates pelvic scute, lacking spine) (A KAUM-I. 94521, paratype of S. eldorado sp. nov. in fresh condition, 43.4 mm SL, Ha Long Bay, northern Vietnam B, E, F KAUM-I. 113148, paratype of S. eldorado sp. nov., 55.3 mm SL, Ke-tzu-liao, south-western Taiwan C ZUMT 62056, paratype of S. diabolus sp. nov., 38.4 mm SL, Singapore D KAUM-I. 94509, paratype of S. eldorado sp. nov., 41.4 mm SL, Ha Long Bay, northern Vietnam) (B, D, E and F alizarin stain).

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 6. A lateral B dorsal and C ventral views of preserved holotype of S. diabolus sp. nov., IPMB-I 13.00001, 49.7 mm SL, Teluk Bahang, Penang, Malaysia D lateral view of preserved paratype of S. diabolus sp. nov., ZUMT 62056, 37.3 mm SL, Singapore. Scale bars: 2 mm.

Figure 7. Relationships of total gill raker numbers (TGR) on A first gill arch (1 GA) B second gill arch (2 GA) C third gill arch (3 GA) and D fourth gill arch (4 GA) to standard length in Stolephorus bengalensis (red circles), S. diabolus sp. nov. (yellow squares), S. eclipsis sp. nov. (green diamonds) and S. eldorado sp. nov. (blue triangles).

Figure 8. Relationships of A orbit diameter (as % of standard length; SL) B third dorsal-fin ray length (as % of SL) C anal-fin base length (as % of SL) D pelvic-fin length (as % of SL) and E distance between posterior ends of supramaxilla and maxilla (SMX-MX) in Stolephorus bengalensis (red circles), S. diabolus sp. nov. (yellow squares), S. eclipsis sp. nov. (green diamonds) and S. eldorado sp. nov. (blue triangles).