Stolephorus falco sp. nov.

Figs 1, 2; Tables 1–4 New English name: Falcon Anchovy

Holotype.

• ZMH 28689, 58.8 mm SL, off Kualu, Sumatera Utara, Sumatra, Indonesia, 15 Aug. 1898.

Paratypes.

• 2 specimens, 58.4–63.3 mm SL, all specimens collected with the holotype. ZMH 28749, 63.3 mm SL, KAUM –I.220780 (formerly ZMH 28689), 58.4 mm SL.

Diagnosis.

A species of Stolephorus with the following combination of characters: 1 UGR 17 or 18, 1 LGR 22 or 23, 1 TGR 39–41; 2 UGR 13 or 14, 2 LGR 20–22, 2 TGR 33–36; 3 UGR 10, 3 LGR 12 or 13, 3 TGR 22 or 23; 4 UGR 7 or 8 (8), 4 LGR 10, 4 TGR 17 or 18; scales rows in longitudinal series 31 or 32; maxilla long, 22.8–23.5 % of SL, its posterior tip slightly not reaching to posterior margin of opercle; pelvic fin long, 11.9–12.2 % of SL, its posterior tip reaching to vertical through 3 rd to 4 th dorsal-fin ray origin when depressed; paired dark longitudinal lines on dorsum posterior to dorsal fin, but not on anterior to dorsal fin; body scales non-deciduous, with densely reticulated grooves; head large, 26.3–27.5 % of SL; body deep, 28.8–28.9 % of SL.

Description.

Counts and measurements (expressed as percentages of SL) are shown in Tables 1, 2. Data for the holotype are given in parentheses (if different). Body strongly compressed, oblong, deepest at dorsal-fin origin. Dorsal contour elevated from snout tip to dorsal-fin origin, thereafter gently decreasing to uppermost point of caudal-fin base. Ventral profile of body lowering from lower-jaw tip to pelvic-fin insertion thereafter gently rising to lowermost point of caudal-fin base. Abdomen from region between pectoral fins to pelvic-fin insertion covered with 4 spine-like scutes backwardly projecting. Single spine projecting backwardly on pelvic scute. No scutes abdomen before pectoral fins and posterior to pelvic fin. Single spine-like predorsal scutes located just before dorsal-fin origin. Pectoral fin triangular, dorsal, ventral, and posterior margins of fin nearly linear; fin insertion slightly posterior to posterior margin of opercle, lower than level of snout tip; posterior tip of fin pointed, not reaching to pelvic-fin insertion; uppermost ray unbranched, all other rays branched. Elongated triangular axillary scale shorter than pectoral fin; located above pectoral-fin insertion. Pelvic fin triangular, anterior and posterior margins nearly linear; fin insertion anterior to dorsal-fin origin; posterior tip pointed; depressed fin posteriorly reaching to vertical through origin of 3 rd (4 th) dorsal-fin ray; anteriormost fin ray unbranched, all other rays branched. Axillary scale of pelvic fin detached in holotype (elongated triangular axillary scale shorter than pectoral fin; located above pelvic-fin insertion in paratype). Dorsal fin triangular, anterior and posterior profiles nearly linear; fin origin posterior to posteriormost point of pelvic-fin base; three anteriormost rays unbranched, all other rays branched; depressed fin not posteriorly beyond vertical through posteriormost point of anal-fin base. Origin of anal fin located just below 9 th (11 th or 12 th) dorsal-fin ray origin; three anterior fin rays unbranched, all other rays branched. Elongated sheath scales on bases of dorsal and anal fins. Caudal fin forked, posterior tips of both lobes pointed, outer contour of each lobe nearly straight (lower part of lower lobe broken in holotype). Anus just in front of anal-fin origin. Snout rounded, projecting beyond lower-jaw tip. Orbit oval, entirely covered with thin adipose eyelid. Eye and pupil round. Nostrils paired close to each other, positioned just anterior to orbit. Mouth large, inferior, oblique to body axis, extending backward to posterior margin of orbit. Maxilla long, posterior tip slightly not reaching to posterior margin of opercle. Lower jaw slender. Single rows of conical teeth on both jaws and palatine. Several conical teeth on vomer. Several rows of conical teeth on pterygoids and dorsal surfaces of basihyal and basibranchial. Single row of fine teeth on dorsal surface of hyoid arch. No tongue. Posterior margin of preopercle round, not intended. No serration on posterior margins of preopercle and opercle. Gill membrane without serrations. Pseudobranchial filaments covered with thin fleshy membrane; length of longest filament less than eye diameter. Gill rakers presenting on inner surfaces of 1 st to 4 th gill arches and posterior surface of 3 rd epibranchial; gill rakers long, slender, and rough. Isthmus muscle long, reaching anteriorly to posterior margin of gill membranes. Urohyal hidden by isthmus muscle. Body scales cycloid, not deciduous, almost remain on type specimens; dense reticulation of grooves on body scales (Fig. 2). No scales on head and fins except for broad, triangular sheath on caudal fin. Lateral line absent.

Coloration of preserved specimens.

Body uniformly, light brown. Silver longitudinal band slightly narrower than eye diameter running from upper part of cleithrum to caudal-fin base. Melanophores scattered along dorsal-fin rays and fin bases of dorsal and anal fins. No melanophores on pectora, pelvic, and anal fins. Melanophores scattered on caudal fin-rays, dense on outer margin of fin. Melanophores scattered on posterior margins of scales on upper part of lateral surface of body. Pair of dark patches on parietal region. Melanophores densely gathered on occipital region forming single patch. Paired longitudinal dark lines on dorsum posterior to dorsal fin, but no lines on dorsum anterior to dorsal fin. Lateral surface of head including opercle uniformly silver. Snout and both jaws translucent. Melanophores not scattered on mouth roof, gill rakers, gill arches, gill filaments, and inner surfaces of opercle and hyoid arch (few melanophores scattered on innersurface on hyoid arch in KAUM –I.220780). Fresh coloration unknown.

Distribution.

Stolephorus falco sp. nov. is currently known only from Kualu, North Sumatra, Indonesia.

Etymology.

The specific name falco is derived from Latin meaning “ falcon ”, in reference to the talon-like hard spine on the dorsum of the species.

Comparisons.

The new species is assignable to the genus Stolephorus, as determined by Whitehead et al. (1988) and Wongratana et al. (1999), having a long isthmus muscle anteriorly reaching to the posterior margin of the gill membrane, the urohyal embedded in the isthmus muscle, prepelvic scutes, and the anal-fin origin just positioned below the middle of the dorsal-fin base and lacking of the postpelvic scutes.

Based on its predorsal scute and backward spine on pelvic scute, Stolephorus falco sp. nov. is considered as probable member of the “ spined Stolephorus ” clade (see the Introduction). Among the “ spined Stolephorus ”, the new species is easily distinguished from S. dubiosus and S. taurus by its fewer gill rakers [1 TGR 39–41, 2 TGR 33–36, 3 TGR 22–23, 4 TGR 17–18, and gill rakers on posterior surface of 3 rd epibranchial 4 in S. falco sp. nov. vs 45–53, 39–48, 26–31, 20–25, and 5–7 in S. dubiosus; 45–49, 39–42, 24–28, 19–22, and 5 or 6 (rarely 4 or 7) in S. taurus; Table 3], fewer scale rows in longitudinal series (31–32 vs 34–37 in S. dubiosus; 33–35 in S. taurus; Table 4), longer head (26.3–27.5 % of SL vs 23.2–26.4 % in S. dubiosus; 23.5–26.5 % in S. taurus; Fig. 3 A), pre-dorsal-fin length [55.8–56.2 % of SL vs 51.8–55.9 % in S. dubiosus; 50.3–55.2 % (rarely 56.2 %) in S. taurus; Fig. 3 B], distance between snout tip and pectoral-fin insertion (28.3–28.5 % of SL vs 25.2–28.1 % in S. dubiosus vs 24.4–27.3 % in S. taurus; Fig. 3 C), postorbital region (15.2–16.2 % vs 12.7–14.9 % in S. dubiosus; 12.6–14.5 % in S. taurus; Fig. 3 D), maxilla (22.8–23.5 % of SL vs 19.2–22.2 % in S. dubiosus; 19.9–21.9 % in S. taurus; Fig. 3 E), 3 rd dorsal-fin ray (21.3 % of SL vs 16.8–19.1 % in S. dubiosus; 18.6–20.2 % in S. taurus; Fig. 3 F) and deeper body (28.8–28.9 % of SL vs 20.4–27.3 % in S. dubiosus; 21.3–24.4 % in S. taurus; Fig. 3 G), D – P 2 (29.6–30.7 % of SL vs 23.1–28.0 % in S. dubiosus; 22.3–27.2 % in S. taurus; Fig. 3 H), D – A (29.3–29.9 % vs 21.8–27.9 % in S. dubiosus; 23.2–26.3 % in S. taurus; Fig. 3 I), and caudal peduncle (12.2–13.7 % of SL vs 9.5–11.9 % in S. dubiosus vs 10.2–12.4 % in S. taurus; Fig. 3 J). Moreover, the new species further differs from S. dubiosus in having a wider eye diameter (7.2–7.3 % of SL vs 5.9–7.3 % in S. dubiosus; Fig. 3 K), pectoral fin (17.7–19.3 % of SL vs 15.6–17.7 %; 3 L), pelvic fin (11.9–12.2 % of SL vs 9.5–10.8 %; Fig. 3 M), lower jaw (18.0–18.2 % of SL vs 15.4–17.7 %; Fig. 3 N), 2 nd dorsal-fin ray (8.3–10.2 % of SL vs 4.9–8.7 %; Fig. 3 O), 2 nd anal-fin ray (7.2–7.5 % of SL vs 4.3–6.4 %; Fig. 3 P), and 3 rd anal-fin ray (15.1–18.2 % vs 13.4–15.6 %; Fig. 3 Q), the pelvic fin posteriorly reaching to vertical through 3 rd to 4 th dorsal-fin ray origin [vs short of the dorsal-fin origin (rarely reaching to vertical through 1 st or 2 nd dorsal-fin ray origin) in S. dubiosus]. Moreover, anal-fin base length of S. falco sp. nov. is longer than that of S. taurus (20.7–23.5 % of SL in S. falco sp. nov. vs 18.7–20.9 % in S. taurus; Fig. 3 R).

Additionally, the new species differs from S. tri in having more gill rakers [1 TGR 39–41 and 2 TGR 33–36 in S. falco sp. nov. vs 32–38 (rarely 39) and 27–32 in S. tri; Table 3), fewer scale rows in longitudinal series (31–32 vs 33–36; Table 4), longer pre-dorsal-fin length [55.8–56.2 % of SL vs 49.1–55.5 % (rarely 57.6 %); Fig. 3 B], pelvic fin (11.9–12.2 % of SL vs 8.1–10.8 %; Fig. 3 M), postorbital region (15.2–16.2 % of SL vs 12.4–15.2 %; Fig. 3 D), interorbital region (6.2–6.5 % of SL vs 4.9–6.3 %; Fig. 3 S), 2 nd dorsal-fin ray (8.3–10.2 % of SL vs 6.0–8.6 %; Fig. 3 O), 3 rd dorsal-fin ray (21.3 % of SL vs 16.5–18.0 %; Fig. 3 F), 2 nd anal-fin ray (7.2–7.5 % of SL vs 4.0–6.7 %; Fig. 3 P), and 3 rd anal-fin ray (15.1–18.2 % vs 11.9–15.2 %; Fig. 3 Q), shorter snout (3.1–3.5 % of SL vs 3.5–4.3 %; Fig. 3 T), deeper body (28.8–28.9 % of SL vs 20.7–25.8 %; Fig. 3 G), D – P 2 (29.6–30.7 % of SL vs 23.7–29.1 %; Fig. 3 H), D – A (29.3–29.9 % vs 22.9–27.6 %; Fig. 3 I), and caudal peduncle (12.2–13.7 % of SL vs 8.8–11.9 %; Fig. 3 J), the pelvic fin posteriorly reaching to vertical through 3 rd to 4 th dorsal-fin ray origin (vs short of the dorsal-fin origin). Dorsal pigmentation from the occipital area to the dorsal-fin origin also separates S. falco sp. nov. (no dark lines; Fig. 1 B) and S. tri (usually paired dark lines; Hata et al. 2019: fig. 19).

Stolephorus falco sp. nov. most closely resembles S. baganensis, as the former was previously identified as the latter in by Hata et al. ’ s (2022 b: 12) identification keys on the basis of published information. However, on direct examination of the type specimens, the new species is clearly separated from S. baganensis by longer head [26.3–27.5 % of SL vs 22.3–26.7 % (<26 % in specimens> 50 mm SL) in S. baganensis; Fig. 3 A], pre-dorsal-fin length [55.8–56.2 % of SL vs 50.6–55.4 % (rarely 56.5 %, only 1 of 82 specimens); Fig. 3 B], eye diameter (7.2–7.3 % of SL vs 5.3–7.2 %; Fig. 3 K), pelvic fin (11.9–12.2 % of SL vs 8.7–11.6 %; Fig. 3 M), postorbital region (15.2–16.2 % vs 12.2–14.8 %; Fig. 3 D), maxilla (22.8–23.5 % of SL vs 19.2–22.5 %; Fig. 3 E), lower jaw (18.0–18.2 % of SL vs 15.5–18.1 %; Fig. 3 N), and 3 rd dorsal-fin ray (21.3 % of SL vs 16.2–20.3 %; Fig. 3 F), 2 nd anal-fin ray (7.2–7.5 % of SL vs 3.6–7.0 %; Fig. 3 P), deeper body (28.8–28.9 % of SL vs 20.2–26.1 %; Fig. 3 G), D – P 2 (29.6–30.7 % of SL vs 21.4–29.0 %; Fig. 3 H), D – A (29.3–29.9 % of SL vs 21.6–27.9 %; Fig. 3 I), and caudal peduncle depth (12.2–13.7 % of SL vs 7.9–12.1 %; Fig. 3 J), and fewer scale rows in longitudinal series (31 or 32 vs 33–37; Table 4).

In addition, the new species has the deepest body of all species of the genus (the second largest species is S. dubiosus, whose body depth reaches 27.3 % of its length; Hata et al. 2022 b), but it also features among the fewest scale rows in longitudinal series (the second is Stolephorus brachycephalus Wongratana, 1983, a species with 32–34 scales; Hata and Motomura 2024 c).

Remarks.

Because S. falco is here named from only three known specimens collected from Kwalu (northeastern Sumatra), its exact distribution is unknown. However, the new species has never been recorded in the ichthyofaunal surveys in neighboring areas such as Thai Andaman Sea (Matsuura and Kimura 2005; Kimura et al. 2009 a; Satapoomin 2011; Hata et al. 2024 b); Penang on the west coast of the Malay Peninsula (Lavoué et al. 2022), Johor Strait at the southern tip of the Malay Peninsula (Kimura et al. 2015), east coast of Malay Peninsula (Matsunuma et al. 2011; Motomura et al. 2021; Giat et al. 2021), and eastern Indonesia (White et al. 2013). It is, therefore, likely to be endemic to the vicinity of the type locality in Sumatra.

Comparative materials.

Stolephorus baganensis: 82 specimens, 27.3–83.5 mm SL: listed by Hata et al. (2022 b) and 51 additional specimens: MNHN 2001 -3142, 83.5 mm SL, off Vung Tau, Vietnam; MZB 28362, 78.6 mm SL, off Tanjung Pasir, Java, Indonesia (obtained at Tanjung Pasir Fish Market), NMMB-P 32374, 22 specimens, 41.9–63.6 mm SL, Matang, Perak, Malaysia; QM I.28329, 50.5 mm SL, Lassa River estuary, Kuala Matu, Sarawak, Borneo, Malaysia; RMNH.PISC.85266, 2 specimens, paralectotypes of Engraulids tri, 66.8–75.4 mm SL, Indonesia; USMFC (82) 00078, 62.5 mm SL, Batu Lintang, Merbok estuary, Kedah, Malaysia (5 ° 37 ' 26.4 " N, 100 ° 23 ' 39.1 " E); USNM 316674, 2 specimens, 62.2–66.9 mm SL, Vung Tau, Ba Ria Vung Tau, Vietnam (obtained at fish market in Vung Tau); ZMUC 41, 48.4 mm SL, Rangoon, Myanmar; ZMH 10675, 4 of 11 specimens, 34.4–43.1 mm SL, Kuala Langat, Selangor, Malaysia; ZMH 10676, 4 of 8 specimens, 37.5–50.9 mm SL, Kuala Selangor, Selangor, Malaysia; ZRC 39790, 12 specimens, 42.7–68.7 mm SL, Matang, Perak, Malaysia. Stolephorus dubiosus: 31 specimens, 49.2–78.1 mm SL: listed by Hata et al. (2022 b) and 8 additional specimens, ANSP 61760, paratypes of Stolephorus dubiosus, 2 specimens, 49.5–58.1 mm SL, estuary of Chao Phraya River, Paknam, Thailand; BMNH 1989.2. 2.74–75, 2 specimens, 49.2–59.2 mm SL, off Semarang, Java, Indonesia, 10 m depth; BMNH 1981.7. 29.246, 64.2 mm SL, Takisung, Tanah Laut, Kalimantan, Indonesia; RMNH.PISC.85265, 3 specimens, paralectotypes of Engraulids tri, 64.9–73.8 mm SL, Indonesia; ZMA 108.373, 56.6 mm SL, Soerabaja, Java, Indonesia. Stolephorus taurus: 26 specimens, 39.8–71.3 mm SL: listed by Hata et al. (2022 b) and 6 additional specimens, BMNH 1889.2. 1.1840, paratype of Stolephorus dubiosus, 68.1 mm SL, Orissa, India; BMNH 1969.4. 22.1803, 71.3 mm SL, Godavari Estuary, Andhra Pradesh, India; MNHN 992, 1 of 3 specimens, 57.7 mm SL, Ganges, India; RMNH.PISC.8587, 68.9 mm SL, Orissa, India; ZMUC P.18273 –18274, 2 specimens, 45.2–47.6 mm SL, Tharangambadi, Tamil Nadu, India. Stolephorus tri: 41 specimens, 45.5–95.1 mm SL: listed by Hata et al. (2022 b) and 14 additional specimens, BC 63-1348, 77.9 mm SL, Muar Market, Johor, Malaysia; BMNH 1977.11. 30.163–166, 2 of 4 specimens, 88.1–92.6 mm SL, Surat Thani Province, Thailand; RMNH.PISC.17735, 89.6 mm SL, Pulau Weh, northern Sumatra, Indonesia; RMNH.PISC.24961, 6 specimens, paralectotypes of Engraulids tri, 72.2–86.5 mm SL, Indonesia; UMMZ 225767, 73.9 mm SL, approx. 27 km southeast of estuary of Hau River (Mekong Basin), Vietnam (9 ° 14 ' 42.0 " N, 106 ° 17 ' 36.0 " E); USMFC (82) 00031, 80.2 mm SL, Sungai Batu, Malaysia; USMFC (82) 00082, 82.3 mm SL, USMFC (82) 00083, 78.0 mm SL, Batu Maung fish landing port, Penang, Malaysia.