Sardinella electra Hata & Motomura 2019, n. sp.

Sardinella electra n. sp.

[New English name: Island Sardinella; new standard Japanese name: Shimakaze-iwashi]

(Figs. 1–2; Table 1)

Holotype. URM-P 32904, 91.8 mm SL, Ishigaki Fishing Port, Ishigaki Island, Yaeyama Islands, Japan, 6 Nov. 1994, line-fishing.

Paratypes. 17 specimens, 82.4–110.5 mm SL. KAUM–I. 114809, 93.4 mm SL, KAUM–I. 114810, 90.4 mm SL, KAUM–I. 114811, 102.2 mm, SL, URM-P 32905, 86.6 mm SL, URM-P 32 906, 91.6 mm SL, URM-P 32907, 96.6 mm SL, URM-P 32908, 109.9 mm SL, URM-P 3 2909, 85.4 mm SL, URM-P 32910, 90.9 mm SL, URM-P 32911, 103.0 mm SL, URM-P 32912, 93.2 mm SL, URM-P 32913, 92.5 mm SL, URM-P 32914, 91.5 mm SL, URM-P 32915, 99.5 mm SL, URM-P 32 916, 82.4 mm SL, URM-P 32917, 90.9 mm SL, URM-P 32918, 99.2 mm SL, collected with the holotype.

Diagnosis. A species of Sardinella with the following combination of characters: caudal fin with distinct black tips; lateral body scales with centrally continuous or overlapping vertical striae and few perforations, without pores posteriorly; black spot on dorsal-fin origin; gill rakers 38–46 (modally 41) in upper series on 1st gill arch, 67–76 (70, 72, 73) in lower series, 105–121 (114) in total; gill rakers 36–43 (38) in upper series on 2nd gill arch, 69–78 (70) in lower series, 107–120 (107, 111) in total; gill rakers 32–39 (36) in upper series on 3rd gill arch, 53–66 (57, 59) in lower series, 88–104 (93) in total; gill rakers 26–31 (28) in upper series on 4th gill arch, 39–52 (45, 46) in lower, 65–82 (72, 75) in total; gill rakers 25–31 (26) on posterior face of third gill arch.

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Description. Counts and measurements, expressed as percentages of SL, are given in Table 1. Data for the holotype are presented first, followed by paratype data in parentheses. Body oblong, compressed, deepest at dorsalfin origin. Dorsal profile of body elevated from snout tip to dorsal-fin origin, thereafter decreasing to uppermost point of caudal-fin base. Ventral profile of body ventrally decurved from lower-jaw tip to pelvic-fin insertion, thereafter increasing to ventralmost point of caudal-fin base. Abdomen from isthmus to anus with 31 (30 to 32) scutes. Predorsal scutes absent. Anteriormost point of pectoral-fin insertion anterior to posteriormost point of opercle. Upper, posterior and ventral margins of pectoral fin nearly linear. Posterior tip of pectoral fin pointed. Pectoral-fin axillary scale present. Dorsal-fin origin equal with vertical at posterior tip of pectoral fin (slightly short of or beyond this vertical in paratypes). Dorsal contour of dorsal fin elevated from dorsal-fin origin to posterior tip of 4th (or 5th) dorsal-fin ray, thereafter declining to posteriormost point of last dorsal-fin ray. Posteriormost dorsalfin ray not filamentous. Anteriormost point of pelvic-fin insertion located at vertical through origin of 9th (8th– 10th) dorsal-fin ray. Posterior tip of depressed pelvic fin reaching beyond vertical at posterior end of dorsal-fin base, not reaching to anus. Pelvic-fin axillary scale present. Anal-fin origin posterior to vertical at posteriormost point of dorsal-fin base. Two posteriormost anal-fin rays enlarged. Caudal fin forked. Posterior tip of both lobes of caudal fin pointed. Anus on ventral midline, slightly anterior to anal-fin origin, posterior to midpoint of body. Scales cycloid, thin, except for robust ventral scutes. Scales on lateral surface of body with several centrally continuous or overlapping vertical striae, and with few perforations posteriorly (Fig. 2). Bases of dorsal and anal fins with low scaly sheaths. Predorsal scales paired. No scales on head and fins, except for a broad triangular sheath of scales on caudal fin. Mouth terminal, small, posterior tip of maxilla reaching vertical through anterior margin of iris. Second supramaxilla symmetrical. Premaxilla and hypomaxilla without teeth. Ventral margin of maxilla toothed. Lower jaw with several conical teeth anteriorly. Posterior ramus of lower jaw elevated. Orbit elliptical, eye and iris round. Eyes covered with adipose eyelid posteriorly. Interorbital space flat. Nostrils close to each other, anterior to orbit. No lateral line. Gill rakers long, slender, with small asperities on anterior surface. Pseudobranchial filaments present. Gill opening with two fleshy outgrowths on posterior margin and a large papilla on ventral margin. Posterior margins of preopercle and opercle smooth.

Color of preserved specimens. Body dark brown dorsally, elsewhere yellowish- silver. Black spot on dorsal-fin origin and on distal tips of caudal fin lobes. Melanophores scattered on upper part of dorsal fin and first pectoral-fin ray.

Distribution. Currently known only from Ishigaki Island, Yaeyama Islands, southern Ryukyu Islands, Japan. The species inhabits coastal shallow waters.

Etymology. The specific name electra is derived from the Greek for Elektron, meaning “splendor”, in reference to the brilliant silver body.

Remarks. The new species is assigned to the genus Sardinella, defined by Whitehead (1985) and Munroe et al. (1999) (see “Introduction”), being similar to three other species of Sardinella that are characterized by having black caudal-fin tips (see Whitehead 1985; Sterns et al. 2016). Of the latter three species, Sardinella atricauda (Günther 1868) and Sardinella melanura (Cuvier 1829) can be readily distinguished from the new species by their centrally discontinuous longitudinal striae on the lateral body scales (continuous or overlapping in S. electra) and absence of a black spot on the dorsal-fin origin (black spot present). However, the third species, S. hualiensis (Chu & Tsai 1958), shares with S. electra a black- tipped caudal fin, black spot on the dorsal-fin origin and similar configuration of the striae on the lateral body scales. However, S. electra is distinguished from S. hualiensis by the number of gill-rakers on the first to fourth gill arches (Table 1; Fig. 3), and in having relatively few perforations and no pores posteriorly on the lateral body scales (vs. numerous perforations and pores in S. hualiensis; Fig. 2).

Comparative material examined. Sardinella hualiensis (32 specimens, 88.6–171.1 mm SL): ASIZP 59477, 2 specimens, 149.4–157.9 mm SL, Hualien, Taiwan; ASIZP 66242, 107.5 mm SL, ASIZP 66278, 112.6 m SL, Nan- Fon-Ao, Yi-Lan, Taiwan, trawl; ASIZP 66576, 96.0 mm SL, ASIZP 66578, 88.6 mm SL, Nan-Fon-Ao, Yi-Lan, Taiwan; ASIZP 66660, 92.7 mm SL, Daxi, Yi-Lan, Taiwan; ASIZP 70298, 117.7 mm SL, Hualien, Taiwan, gill net; ASIZP75098, 8 specimens, 152.2–170.4 mm SL, Nan-Fon-Ao, Yi-Lan, Taiwan; BPBM 23190, 140.3 mm SL, Hualien, Taiwan; NMMBP 10116, 129.5 mm SL, Nan-Fon-Ao, Yi-Lan, Taiwan; NMMBP 10515, 155.9 mm SL, How-wan, Pingtung, Taiwan; NMMBP 23138, 132.8 mm SL, Ke-tsu-liao, Kaosiung, Taiwan; NSMT-P 55731, 2 specimens, 123.3–127.4 mm SL, Taitung, Taiwan; NTUM 7567, neotype of Harengula hualiensis, 156.7 mm SL, Hualien, Taiwan, gill net; NTUM 7568, 3 specimens, 153.3–157.2 mm SL, NTUM 7569, 2 specimens, 149.2– 155.6 mm SL, Hualien, Taiwan, gill net; NTUM 14610, 3 specimens, 93.3– 149.1 mm SL, Nanfangao, Yilan County, Taiwan; USNM 403456, 171.0 mm SL, Yelin, Yelin County, Taiwan.