Stolephorus dubiosus Wongratana, 1983

Yamamoto, Takumi, Nakamura, Takashi & Toda, Mamoru, 2022, Fig. 4 in Verification of Natural Marking for Individual Identification Using a Duplex Marking Approach in Ijima's Sea Snakes, (Reptilia: Elapidae)., Zoological Studies 61 (58), pp. 1-16 : 3-11

Stolephorus dubiosus Wongratana, 1983

(English name: Thai Anchovy)

( Figs. 1–6 ; Tables 2, 3)

Stolephorus baganensis baganensis (not of Delsman): Hardenberg 1934: 333 [in part: Susang, Labuan, Batavia (currently Jakarta), Cheribon (Cirebon), Kendal, Semarang, Tuban, Surabaja (Surabaya), and Kumai, Indonesia].

Stolephorus dubiosus Wongratana, 1983: 400 , fig. 18 (in part: original description; type locality: Songkhla Lake, Thailand; other localities: Paknam, Bangkok, Samutsakorn, Nakornsrithammaraj, and Surajthani, Thailand; Aluhaluh on Barito River, Kalimantan, Indonesia); Wongratana 1987a: 107 (in part: Thailand, Malay Peninsula, and Indonesia); Wongratana 1987b: 8 (in part: Gulf of Thailand and Java Sea); Whitehead et al. 1988: 411, unnumbered fig. (in part: Gulf of Thailand to Java Sea); Kottelat et al. 1993: 31, fig. 94 (in part: Sundaland and Thailand); Wongratana et al. 1999: 1734, unnumbered fig. (in part: Gulf of Thailand, Java Sea to Kalimantan); Nakashima 2005: 72 (Samut Prakan Province, Thailand); Jutagate et al. 2009: 123 (Pak Panang Bay and estuary of Pak Panang River, Thailand); Matsunuma 2013: 33, unnumbered fig. (Bang Pakong, Gulf of Thailand, Thailand); Tran et al. 2013: 43, unnumbered fig. (Mekong Delta, southern Vietnam); Kottelat 2013: 55 (Songkhla Lake, Thailand); Rupawan 2017: 132 (Panjan Strait, Riau Province, Sumatra, Indonesia); Hata et al. 2019: 30, fig. 14 (in part: Kuching, Sarawak, Malaysia; Songkhla Lake and Gulf of Thailand, Thailand); Syafei et al. 2020: 4, fig. 2 (Pabean Bay, Indramayu, West Java, Indonesia); Hata et al. 2020b: table 1 (in part: Bangkok, Thailand); Nagao Natural Environment Foundation 2021: 55, unnumbered fig. (Mekong Basin in Vietnam).

Holotype: BMNH 1969.4 .22.1826, 70.0 mm SL, Songkhla Lake , Thailand, 2 May 1966, I. A. Ronquillo.

Non-type specimens: 22 specimens, 49.9–78.1 mm SL. THAILAND: BMNH 1977.11.30.63, 63.2 mm SL, Nakornsrithammaraj; THNHM-F 021231, 68.1 mm SL, THNHM-F 021232, 72.1 mm SL, THNHM-F 021233, 65.6 mm SL, THNHM-F 021234, 60.7 mm SL, THNHM-F 021235, 64.4 mm SL, Bang Pakong River estuary, Chachoengsao Province; THNHM-F 021236, 58.2 mm SL, Gulf of Thailand; THNHM-F 021237, 66.0 mm SL, THNHM-F 021238, 64.5 mm SL, THNHM-F 021239 (cleared and stained), 63.6 mm SL, Thachin River estuary, Muang, Samut Sakhon Province; NSMT-P. 55363, 3 specimens, 55.1–59.1 mm SL, Songkhla Lake, 1.5 m depth, shrimp trap; NSMT-P 127425, 3 specimens, 49.9–59.4 mm SL, Songkhla Lake; URM-P 12176, 65.1 mm SL, Songkhla; URM-P 27308, 59.4 mm SL, URM-P 27309, 63.4 mm SL, Pak Nam, Samut Prakan Province; USNM 119676, 2 specimens, 58.4–62.3 mm SL, Bangpakong River. VIETNAM: NTUM 12329, 78.1 mm SL, Ganh Rai Bay.

Diagnosis: A species of Stolephorus with the following combination of characters: predorsal scute and spine on pelvic scute present; gill rakers on first gill arch 20–24 (modally 21) (upper series), 26–29 (28) (lower series), 46–53 (49) in total; gill rakers on second gill arch 16–19 (16) (upper series), 25–29 (27) (lower series), 41–48 (43) in total; gill rakers on third gill arch 12–14 (13) (upper series), 14–17 (15) (lower series), 27–31 (28) in total; gill rakers on fourth gill arch 8–11 (10) (upper series), 11–14 (12) (lower series), 20–25 (22) in total; prepelvic scutes 5–7 (6); maxilla long, posterior tip just reaching or slightly short of posterior margin of opercle; small teeth on dorsal surface of hyoid bone; posterior border of preopercle convexly rounded; distinct paired dark patches on parietal and occipital regions; no dark lines on dorsum anterior to dorsal-fin origin; double pigmented lines on dorsum from dorsal-fin base end to caudal-fin base; no melanophores below eye or on mandibular tip; posterior tip of pelvic fin usually not reaching vertical through dorsal-fin origin (sometimes reaching to vertical through first or second dorsal-fin ray origin) when depressed; body scales not deciduous, with numerous separations of grooves; pectoral fin short, 15.6–17.4% SL; pelvic fin short, 9.5–10.8% SL; second dorsal-fin ray short, 4.9–8.5% SL; third dorsal-fin ray short, 16.8–19.0% SL; second anal-fin ray short, 4.3–5.9% SL; third anal-fin ray short, 13.4–15.1% SL; interorbit narrow, 21.5–24.8% HL.

Description: Data for holotype presented first, followed by other specimen data 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 gradually elevated from snout tip to dorsal-fin origin, thereafter, nearly linear, gently lowering to uppermost point of caudal-fin base. Ventral profile of head and body gently lowering from snout tip to just below pectoral-fin insertion, thereafter parallel to body axis to anal-fin origin. Ventral contour from anal-fin origin to lowermost point of caudal-fin base gently elevated. Single spine-like scute just anterior to dorsal-fin origin ( Fig. 2 ). Abdomen rounded, covered with five (four to seven) spine-like scutes anterior to pelvic-fin insertion. Pelvic scute attached to pelvic girdle, with a hard backwardly projecting spine ( Fig. 3). No spine-like scutes on ventral surface posterior to pelvic fin. Anus just anterior to anal-fin origin. Snout tip rounded, projecting; snout length less than eye diameter. Mouth large, inferior, ventral to body axis, extending backward beyond posterior margin of eye. Maxilla long, posterior tip pointed, reaching to (or just short of) posterior margin of opercle. Premaxilla and first supramaxilla elongate. Second supramaxilla asymmetrical, lower part larger than upper part. Lower jaw slender. Conical teeth in single rows on each jaw and palatines. Several teeth on vomer. Several rows of teeth on inner surface of pterygoids. Small conical teeth on dorsal surface of hyoid bone. 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 margins of preopercle and opercle rounded, smooth. Subopercle with rounded posterior margin. Gill membrane without serrations. Interorbital space flat. Interorbital 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. 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). Head scales absent. Lateral line absent. Fins scaleless, except for broad triangular sheath of scales on caudal fin. Scales on lateral surface cycloid, thin, not deciduous. Numerous separations of grooves on body scales ( Fig. 4 ). 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 bases of tenth (eighth to eleventh) dorsal-fin ray. Posterior tip of depressed anal fin not reaching caudal-fin base. Uppermost pectoral-fin ray unbranched, inserted below midline of body. Posterior tip of pectoral fin pointed, not reaching vertical through pelvic-fin insertion. Upper, posterior, and lower contours of pectoral fin nearly straight. Pelvic fin shorter than pectoral fin. Posterior tip of depressed pelvic fin not reaching to vertical through dorsal-fin origin (rarely reaching to base of first or second dorsal-fin ray). Caudal fin forked, upper and lower margins of both lobes nearly straight. Posterior tips of both lobes pointed.

Skeleton of hyoid arch ( Fig. 5 ): All branchiostegal rays paddle-shaped (posteriorly broad). No branchiostegal rays connected to hypohyal, two rays on epihyal.

Caudal skeleton ( Fig. 6): Each hypural free, except for second and third conjoined. Dorsal margin of first hypural smooth, without distinct projection. Posterior margins of second and third hypurals broadly concave. Dorsal margins of fourth and fifth hypurals projected anteriorly. Sixth hypural elongate.

Coloration when fresh (based on color photographs of THNHM-F 021231–021235, 021237): Body milky-white, a silver longitudinal band of width subequal to pupil diameter extending from just behind upper opercular margin to caudal-fin base. Lateral surface of head uniformly silver. Snout yellowish-white, semi-translucent. Melanophores scattered on snout tip. Scale pockets on upper part of body yellowish-black. Dorsal fin whitish, semi-translucent, melanophores scattered along fin rays. Pectoral, pelvic, and anal fins uniformly whitish, transparent, without melanophores. Caudal fin yellow, melanophores scattered along fin rays. Posterior margin of caudal fin black. Iris and pupil silver and black, respectively.

Coloration of preserved specimens: Body uniformly pale; silver longitudinal band usually lost. Pairs of distinct dark patches on parietal and occipital regions. Scale pockets on dorsum to upper lateral surface of body margined black. Double pigmented lines dorsally posterior to dorsal fin ( Fig. 1c ). A few melanophores scattered anteriorly on snout. All fins whitish. Melanophores scattered along fin rays of dorsal and caudal fins. Pectoral, pelvic, and anal fins semi-transparent, without melanophores. Caudal fin margined black.

Distribution: Stolephorus dubiosus is distributed in the western Pacific Ocean from southern Vietnam (Mekong Delta) to Songkhla, Thailand (based on specimens examined in this study), although molecular evidence and some literature records indicate that it is also distributed in Sumatra, Java, and Borneo ( Wongratana 1983; Rupawan 2017; Syafei et al. 2020; Fig. 7 ). The species mainly inhabits estuarine or brackish waters of large-scale rivers ( Whitehead et al. 1988; Wongratana et al. 1999; this study).

Morphological comparisons: Stolephorus dubiosus is easily distinguished from all other congeners, except for S. baganensis , Stolephorus tri Bleeker, 1852 , and S. taurus sp. nov., in having a spine-like scute located just anterior to the dorsal-fin origin and a small spine on the pelvic scute. Stolephorus bengalensis Dutt and Babu Rao, 1959 , Stolephorus diabolus Hata, Lavoué and Motomura, 2022 , Stolephorus eclipsis Hata, Lavoué and Motomura, 2022 , and Stolephorus eldorado Hata, Lavoué and Motomura, 2022 also have a spine-like scute just anterior to the dorsal-fin origin, but lack a spine on the pelvic scute ( Whitehead et al. 1988; Wongratana et al. 1999; Kimura et al. 2009; Hata and Motomura 2018a –e 2020 2021a b; Hata et al. 2019 2020a b 2021 2022; Gangan et al. 2020; this study). Stolephorus dubiosus differs from S. baganensis and S. tri in having higher counts of lower gill rakers on the first gill arch [26–29 in S. dubiosus vs. 21–24 (rarely 20 or 25) in S. baganensis and 18–22 in S. tri ]. Stolephorus dubiosus is also distinguished from S. baganensis in having the pelvic fin posteriorly short of the dorsal-fin origin (rarely reaching to vertical through first or second dorsal-fin ray origin in S. dubiosus vs. reaching to vertical through third to fifth dorsal-fin ray origin in S. baganensis ). Dorsal pigmentation from the occipital area to the dorsal-fin origin also separates S. dubiosus (no dark lines) and S. tri (usually paired dark lines; fig. 19 in Hata et al. 2019). Comparisons of S. dubiosus with S. taurus are given under Remarks for the latter.

Remarks: Stolephorus dubiosus was originally described by Wongratana (1983) from specimens collected from the Pacific coast of Thailand, Kalimantan, and northeastern India. Subsequently, the species has been considered distributed in both the eastern Indian and western Pacific oceans ( Whitehead et al. 1988; Wongratana et al. 1999). However, specimens from the Indian Ocean previously identified as S. dubiosus are newly recognised herein as a new species (described below), the distributional range of true S. dubiosus therefore being restricted to the western Pacific Ocean ( Fig. 7 ). Before S. dubiosus was described by Wongratana (1983), the species had been frequently confused with S. baganensis . However, because specimens collected from Indonesia, reported by Hardenberg (1934) as S. b. baganensis , had 25–29 lower gill rakers on the first gill arch, they probably included S. dubiosus .

Stolephorus taurus sp. nov. (English name: Bengal Spined Anchovy) ( Fig. 8 ; Tables 2, 3) urn:lsid:zoobank.org:act:457E9BDD-B565-4CCD-80C8-83F92055D3B7

Anchoviella baganensis baganensis (not of Delsman): Dutt and Babu Rao, 1959: 160 (Kakinada, Andhra Pradesh, India).

Stolephorus dubiosus (not of Wongratana): Wongratana 1983: 400 (in part: Orissa, India); Wongratana 1987a: 107 (in part: Bay of Bengal); Wongratana 1987b: 8 (in part: Bay of Bengal); Whitehead et al. 1988: 411 (in part: northern part of Bay of Bengal); Kottelat et al. 1993: 31 (in part: India); Wongratana et al. 1999: 1734 (in part: northern part of Bay of Bengal); Hata et al. 2019: 30 (in part: India); Gangan et al. 2020: 566, fig. 5 (Digha, Kolkata, India); Hata et al. 2020b: table 1 (in part: India).

Holotype: OCF-P 10434, 52.2 mm SL, estuary of Hooghly River , West Bengal, India (purchased in a fish market in Kolkata, West Bengal, India), 9 June 1985.

Paratypes: 19 specimens, 39.8–57.7 mm SL (all purchased with the holotype): KAUM –I. 157580, 46.5 mm SL, KAUM –I. 157581, 53.2 mm SL, NSMT-P 141123, 49.0 mm SL, NSMT-P 141124, 48.6 mm SL, URM-P 10942, 5 specimens, 44.9–53.2 mm SL, URM-P 10943, 10 specimens, 39.8–46.7 mm SL.

Diagnosis: A species of Stolephorus with the following combination of characters: predorsal scute and spine on pelvic scute present; gill rakers on first gill arch 19–22 (modally 21) (upper series), 25–29 (26) (lower series), 45–49 (48) in total; gill rakers on second gill arch 14–16 (15) (upper series), 24–26 (25) (lower series), 39–42 (40) in total; gill rakers on third gill arch 11 or 12 (12) (upper series), 13–16 (14) (lower series), 24–28 (26) in total; gill rakers on fourth gill arch 8–10 (9) (upper series), 11 or 12 (11) (lower series), 19–22 (20) in total; prepelvic scutes 4–6 (5); maxilla long, posteriorly just reaching or slightly short of posterior margin of opercle; small teeth on dorsal surface of hyoid bone; posterior border of preopercle convexly rounded; distinct paired dark patches on parietal and occipital regions; no dark lines on dorsum anterior to dorsal-fin origin; double pigmented lines on dorsum from end of dorsal-fin base to caudal-fin base; no melanophores below eye or on tips of snout and mandible (sometimes a few on snout); posterior tip of pelvic fin reaching to third to sixth dorsal-fin ray base when depressed; body scales not deciduous, with relatively a few separations of grooves; pectoral fin long, 17.8–18.7% SL; pelvic fin long, 11.6–12.7% SL; second dorsal-fin ray long, 8.7– 10.0% SL; third dorsal-fin ray long, 19.5–20.2% SL; second anal-fin ray long, 6.0–7.3% SL; third anal-fin ray long, 15.8–17.5% SL; interorbit wide, 25.2–28.3% HL.

Description: Data for holotype presented first, followed by paratype data in parentheses (if different). Counts and measurements, expressed as percentages of SL or HL, are given in tables 2 and 3.

Body laterally compressed, elongate, deepest at dorsal-fin origin. Dorsal profile of head and body gradually elevated from snout tip to dorsal-fin origin, thereafter gently lowering to uppermost point of caudal-fin base. Ventral contour of head and body lowering from snout tip to just below pectoral-fin insertion, subsequently parallel to body axis to anal-fin origin. Ventral profile from anal-fin base to lowermost point of caudal-fin base gradually elevated. Abdomen rounded, covered with five (four to six) spine-like scutes anterior to pelvic-fin insertion. Pelvic scute joined to pelvic girdle, former with hard backwardly projecting spine. No spine like scutes on ventral surface posterior to pelvic fin. Single spine-like scute just anterior to dorsal-fin origin. Anus just anterior to anal-fin origin. Snout tip rounded, projecting; snout length less than eye diameter. Mouth large, inferior, ventral to body axis, extending backward beyond posterior margin of eye. Maxilla long, posterior tip pointed, just short of or just reaching posterior margin of opercle. Lower jaw slender. Conical teeth in single rows on each jaw and palatines. Several teeth on vomer. Several rows of teeth on inner surface of pterygoids. Small teeth on dorsal surface of hyoid bone. 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 margins of preopercle and opercle smoothly rounded. Subopercle with rounded posterior margin. Gill membrane without serrations. Interorbital space flat. Interorbital 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. 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. Head scales absent. Fins scaleless, except for broad triangular sheath of scales on caudal fin. Scales on lateral surface cycloid, thin, not deciduous. Relatively a few separations of grooves on body scales ( Fig. 9 ). 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 bases of tenth (ninth to twelfth) dorsal-fin ray. Posterior tip of depressed anal fin not reaching caudal-fin base. Uppermost pectoral-fin ray unbranched, inserted below midline of body. Posterior tip of pectoral fin pointed, not reaching vertical through pelvic-fin insertion. Upper, posterior, and lower contours of pectoral fin nearly straight. Pelvic fin shorter than pectoral fin. Posterior tip of depressed pelvic fin reaching to vertical through fourth (third to sixth) dorsal-fin ray base. Caudal fin forked, upper and lower margins of both lobes nearly straight. Posterior tips of both lobes pointed.

Coloration of preserved specimens: Body uniformly pale ivory with whitish longitudinal band, width slightly less than pupil diameter, from just behind upper opercular margin to caudal-fin base. Pairs of dark patches on parietal and occipital regions. No dark lines on dorsum anterior to dorsal fin. Double broken lines of melanophores on dorsum from end of dorsal-fin base to caudal-fin base. Melanophores scattered along posterior margin of dorsal scale pockets. No melanophores on snout, suborbital area and tips of both jaws. Melanophores densely scattered in gill opening. All fins whitish, semi-transparent. Melanophores scattered along caudal-fin rays.

Distribution: Currently known from northern Bay of Bengal. According to Dutt and Babu Rao (1959; as S. baganensis baganensis ) and Wongratana (1983; as S. dubiosus ), S. taurus occurs westward to at least the Godavari River estuary, Andhra Pradesh, India. Moreover, molecular evidence indicated that the new species also occurs in the western part of Bangladesh ( Fig. 7 ). Stolephorus taurus mainly inhabits estuaries or brackish waters. In the coastal area of West Bengal State, India, it is abundantly fished and marketed fresh or dried.

Etymology: The specific name taurus is derived from Greek meaning “bull”, in reference to the hard spine on the dorsum of the species.

Morphological comparisons: The new species is assignable to the genus Stolephorus , as defined by Whitehead et al. (1988) and Wongratana et al. (1999), due to having a long isthmus muscle reaching anteriorly to the posterior margin of the gill membrane, prepelvic scutes, and hidden urohyal, and the absence of postpelvic scutes.

Stolephorus taurus most closely resembles S. dubiosus , both sharing a predorsal scute, spine on the pelvic scute, long maxilla, posteriorly just reaching or slightly beyond the posterior opercular margin, double pigmented lines on the dorsum from the end of the dorsal-fin base to the caudal-fin base (not before the dorsal-fin origin), non-deciduous scales, and 25 or more lower gill rakers on the first gill arch ( Wongratana 1983 1987a b; Whitehead et al. 1988; Wongratana et al. 1999; Kimura et al. 2009; Hata and Motomura 2018a –e; Hata et al. 2019 2020a b 2021 2022; Gangan et al. 2020; this study). However, the new species can be distinguished from S. dubiosus by the longer pectoral (17.8–18.7% SL in S. taurus vs. 15.6–17.4% in S. dubiosus ) and pelvic fins (11.6–12.7% SL vs. 9.5–10.8%), the latter posteriorly reaching to vertical through the base of the third to sixth dorsal-fin rays when depressed [vs. usually not reaching to vertical through dorsal-fin origin (sometimes reaching to vertical through base of first or second dorsal-fin rays)], longer second dorsal-fin (8.7–10.0% SL vs. 4.9–8.5%), third dorsal-fin (19.5– 20.2% SL vs. 16.8–19.0%), second anal-fin (6.0–7.3% SL vs. 4.3–5.9%) and third anal-fin rays (15.8–17.5% SL vs. 13.4–15.1%), a wider interorbit (25.2–28.3% of HL vs. 21.5–24.8%) ( Table 3; Fig. 10 ), and body scales with relatively few separations formed by grooves (vs. numerous separations; Figs. 4 , 9 ). The new species has been frequently recorded from the Indian coast as S. dubiosus (e.g., Wongratana 1983; Gangan et al. 2020), although prior to the description of the latter, it was occasionally confused with S. baganensis . However, S. taurus can be distinguished from S. baganensis by the higher counts of gill rakers (gill rakers on first, second, third and fourth gill arches 19–22 + 25–29 = 45–49, 14–16 + 24–26 = 39–42, 11 or 12 + 13–16 = 24–28, and 8–10 + 11 or 12 = 19–22, respectively, in S. taurus vs. 15–19 + 21–24 (rarely 20 or 25) = 35–43, 11–14 + 19–23 = 31–37, 9–11 + 11–13 = 20–24, 7–9 + 9–13 = 16–21, respectively, in S. baganensis ) and longer pelvic fin (11.6–12.7% SL in S. taurus vs. 8.7–11.6% in S. baganensis ) ( Hata et al. 2019; this study). Because the mean number of lower gill rakers on the first gill arch of specimens collected from the Bay of Bengal and reported by Dutt and Babu Rao (1959) as Anchoviella baganensis baganensis was 26.21, those specimens probably included S. taurus .

Figures

Fig. 1. Stolephorus dubiosus: (a) Lateral view of holotype (BMNH 1969.4.22.1826, 70.0 mm SL, Thailand); (b) lateral view in fresh condition; (c) dorsal and (d) ventral views in preserved condition of non-type specimen (THMHM-F021237, 66.0 mm SL, Samut Sakhon Province, Thailand).

Fig. 2. (a) Lateral and (b) dorsal views of dorsal-fin origin of Stolephorus dubiosus, NSMT-P 127425, 55.7 mm SL, Songkhla Lake, Thailand (stained with Alizarine Red). Arrows indicate predorsal scute.

Fig. 4. Stained scale removed from right side of midbody (just below dorsal fin) of Stolephorus dubiosus. NSMT-P 127425, 49.9 mm SL, Songkhla Lake, Thailand (left-right inverted). Grooves on posterior part forming numerous separations.

Fig. 5. Left side of left hyoid arch of Stolephorus dubiosus (THNHM-F021239, 63.6 mm SL, cleared and stained). hypo lo, lower hypohyal; hypo up, upper hypohyal; chy, ceratohyal; gha, groove for hyoidean artery; eph, epihyal; inh, interhyal (broken); br, branchiostegal rays (seventh branchiostegal ray detached).

Fig. 7. Distributional records of Stolephorus dubiosus (circles) and S. taurus sp. nov. (triangles). Closed symbols, based on specimens examined in this study; open symbols, based on literature records or molecular evidence.

Fig. 8. Lateral (a), dorsal (b), and ventral (c) views of the holotype of Stolephorus taurus sp. nov., OCF-P 10434, 52.2 mm SL, estuary of Hooghly River, West Bengal, India.

Fig. 9. Stained scale removed from right side of midbody (just below dorsal fin) of paratype of Stolephorus taurus. KAUM–I. 157581, 53.2 mm SL, estuary of Hooghly River, West Bengal, India (left-right inverted). Grooves on scales forming a few separations.

Fig. 10. Morphometric comparisons between Stolephorus dubiosus (open triangles) and S. taurus sp. nov. (closed circles). (a) for pectoral-fin length (P1L; as % of standard length; SL); (b) for pelvicfin length (P2L; as % of SL); (c) for second dorsal-fin ray length (2DRL; as % of SL); (d) for third dorsal-fin ray length (3DRL; as % of SL); (e) for second anal-fin ray length (2ARL; as % of SL); (f) for third anal-fin ray length (as % of SL); (g) for interorbital width (as % of head length; HL) to SL.