Stolephorus lotus, Hata & Motomura, 2022

Hata, Harutaka & Motomura, Hiroyuki, 2022, Stolephorus lotus, a New Anchovy (Teleostei: Clupeiformes: Engraulidae) from the Northern Territory, Australia, Zoological Studies 61 (87), pp. 1-11 : 2-7

Stolephorus lotus sp. nov.

(New English name: Lotus Anchovy)

( Figs. 1 , 2 ; Tables 1–4 ) urn:lsid:zoobank.org:act:0BAA1755-A5F9-4201-B5F6-E7716B9964EB

Holotype: NTM S. 15265-006, 40.0 mm SL, west of Pocock’s Beach , Finke Bay, southern part of Van Diemen Gulf , Northern Territory, Australia (12°13'33"S, 132°09'32"E) 3m depth, 6 July 1999, coll. by A. Pickworth et al.

Paratypes: 29 specimens (31.6–40.6 mm SL), all collected with the holotype: KAUM–I. 157133, 1 (39.8 mm SL); KAUM–I. 157134, 1 (38.6 mm SL); NSMT-P 141107, 1 (39.4 mm SL); NSMT-P 141108, 1 (37.7 mm SL); NTM S. 15265-009, 25 (31.6–40.6 mm SL).

Diagnosis: A species of Stolephorus with the following unique combination of characters: maxilla long, 86.7–92.6% HL (mean 89.4%), its posterior tip just reaching to or slightly beyond posterior margin of opercle; posterior margin of preopercle concave, indented; predorsal scutes absent; prepelvic scutes 6–8 (modally 6); pelvic scute without spine; dorsal fin with three unbranched and 11–13 (modally 13) branched rays; anal fin with three unbranched and 16–18 (modally 17) branched rays, its origin located just below origin of sixth to eighth dorsal-fin ray; 1UGR 15–17 (modally 15), 1LGR 21–23 (modally 22), 1TGR 36–39 (modally 37); 2UGR 10 or 11 (modally 11), 2LGR 19 or 20 (modally 20), 2TGR 29–31 (modally 31); 3UGR 8 or 9 (modally 9), 3LGR 11–12 (modally 12), 3TGR 19–21 (modally 20); 4UGR 6 or 7 (modally 6), 4LGT 8–10 (modally 9), 4TGR 14–17 (modally 15); gill rakers 3 or 4 (modally 4) on hind face of third gill arch; transverse scales 8 or 9 (modally 9); pseudobranchial filaments 16–18 (modally 18); paired dark patches on parietal region; no dark lines on dorsum; no black spots on suborbital area and tip of lower jaw; depressed pelvic fin not reaching posteriorly to vertical through dorsal-fin origin; pre-dorsal fin length short, 48.6–52.9% SL (mean 51.2%); body rather elongate, its depth 15.9–17.7% SL (mean 17.1%); anal-fin base short, 17.2–20.2% SL (mean 18.8%); caudal peduncle long, 20.1–22.8% SL (mean 21.0%).

Description: Data for holotype presented in parentheses. Counts and measurements, expressed as percentages of SL or HL ( Tables 1 and 2 ). 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; abdomen somewhat rounded, covered with six to eight (seven) spine-like scutes; pelvic scute without spine; postpelvic and predorsal 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 beyond posterior margin of eye; maxilla long, its posterior tip pointed, just reaching to or slightly beyond (just reaching to) posterior margin of opercle ( Fig. 2 ); lower jaw slender; single row of conical teeth on both jaws, palatine, and inner side of pterygoid; several distinct conical teeth on vomer; no teeth on upper edges of anterior and posterior ceratohyals; several rows of small fine conical teeth on basihyal and basibranchial; eye large, round, covered with adipose eyelid, laterally on head and 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 preopercle concave, indented ( Fig. 2 ); 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, visible from side of head when mouth opened; single row of small spines on both of anterior and posterior surfaces 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; sensory canal on preopercle having many branches, one of them extending on opercle; branch on opercle finely branched; body scales deciduous, all scales on body and fin bases completely lacking on all specimens examined in this study; 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; three anteriormost rays of dorsal and anal fins unbranched; anteriormost three rays of both dorsal and anal fins closely spaced; first dorsal- and anal-fin rays reduced; anal-fin origin just below base of sixth to eighth (seventh) 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 vertical through dorsal-fin origin; caudal fin forked, posterior tips pointed.

C o l o r a t i o n o f p re s e r v e d s p e c i m e n s: Body uniformly pale, light ivory longitudinal band narrower than eye running just behind upper opercular margin to caudal-fin base. No melanophores scattered on head and dorsum except for paired dark patches on parietal region. Ground color of fin rays transparent, colorless. Melanophores scattered along fin rays of caudal fin and anal-fin base. Melanophores dense, forming a dark spot centrally at base of lower lobe of caudal fin. Melanophores scattered on gill rakers. Peritoneum darkly pigmented. Fresh coloration unknown.

Distribution: Currently known only from Van Diemen Gulf, Northern Territory, Australia.

Biological notes: Ovarian eggs (oval shape, ca. 0.5 and 0.2 mm major and minor diameters, respectively) were found in three paratypes (NTM S. 15265-009), indicating that the species is mature at <40 mm SL.

Etymology: The specific name “lotus ”, to be treated as a noun in apposition, refers to waterlilies, characterized by notched leaves, reminiscent of the indented preopercle of the new species.

Comparisons: Stolephorus lotus sp. nov. is easily distinguished from all congeners, except Stolephorus acinaces Hata, Lavoué and Motomura 2020 , Stolephorus andhraensis Babu Rao 1966 , S. carpentariae , Stolephorus hindustanensis Hata and Motomura 2022 , Stolephorus holodon ( Boulenger 1900) , Stolephorus ronquilloi Wongratana 1983 , and Stolephorus tamilensis Gangan, Pavan-Kumar, Jahageerdar and Jaiswar 2020 in having a long maxilla with the posterior tip just reaching or extending slightly beyond the posterior margin of the opercle, the posterior margin of preopercle indented, no spots on the suborbital area or snout and mandible tips, the pelvic scute without a spine, and predorsal scutes absent ( Whitehead et al. 1988; Wongratana et al. 1999; Kimura et al. 2009; Hata and Motomura 2018a –d 2021a –c, 2022; Hata et al. 2019 2020a b 2021 2022a b; Gangan et al. 2020). The numbers of lower and total gill rakers on first gill arch separate S. lotus (1LGR: 21–23; 1TGR 36–39) from S. hindustanensis (1LGR 24–27; 1TGR 42–46), S. holodon (1LGR 25–30; 1TGR 44–51, based on specimens examined in this study), S. ronquilloi (1LGR 28 or 29; 1TGR 47–49), and S. tamilensis (1LGR 25–28; 1TGR 40–47). Moreover, the new species differs from S. hindustanensis and S. ronquilloi in lacking double dark lines on the dorsum posterior to the dorsal fin (vs. distinct double pigmented lines exist in the other two) and in having an elongate body (body depth 15.9–17.7% of SL in S. lotus vs. more than 21.1%). Stolephours lotus is further distinguished from S. tamilensis by its slender body (body depth 15.9–17.7% of SL in S. lotus vs. 19.9–23.4% of SL in S. tamilensis ), greater distance between the snout tip to the pectoral-fin insertion (24.8–26.7% of SL vs. 21.6–24.0%), and the longer maxilla (86.7–92.6% of HL vs. 64.4–76.7%). In addition, the new species differs from S. carpentariae in having the anal fin with 16–18 branched fin rays (vs. 19 or 20 in S. carpentariae ), its origin below the sixth to eighth dorsal-fin ray bases (vs. second to sixth dorsal-fin rays) and 16–18 pseudobranchial filaments (vs. 11–14) ( Wongratana 1987a b; Whitehead et al. 1988; Wongratana et al. 1999; Gangan et al. 2020; Hata and Motomura 2022; this study).

Counts of longitudinal series of scale rows and predorsal scales of S. lotus sp. nov. [37–39 (modally 38) and 20 or 21 (20), respectively] are higher than those in S. acinaces [35–38 (36) and 18 or 19 (19), respectively] and S. andhraensis [35–38 (36) and 17–19 (19), respectively; Table 3 ]. In addition, the anal-fin origin in S. lotus sp. nov. is located more anteriorly than in S. acinaces and S. andhraensis (anal fin originating below bases of sixth to eighth dorsal-fin rays in S. lotus sp. nov. vs. eighth to tenth dorsal-fin rays). Also, the number of branched dorsal-fin rays in the new species is usually lower than in S. acinaces and S. andhraensis (11–13 vs. 12–14, respectively; Table 4). The new species is also distinguished from S. acinaces by its shorter head [22.2–25.1% SL (22.2–24.0% in specimens 35–41 mm SL) vs. 23.0–25.5% (24.0–25.5% in specimens 35–41 mm SL)] and predorsal-fin length (48.6–52.9% SL vs. 51.8–55.8%), a narrower body (15.9–17.7% SL vs. 17.0–21.9%), and longer maxilla (86.7–92.6% HL vs. 75.5–87.4%) ( Fig. 3 , Table 2 ; Hata et al. 2020b: table 3). It differs from S. andhraensis in having slightly higher counts of TGR on each gill arch (36–39, 29–31, 19–21 TGR on 1st, 2nd, and 3rd gill arches, respectively vs. 33–37, 26–29, 17–19, respectively in S. andhraensis ) and a longer caudal peduncle (20.1–22.8% SL vs. 16.9–19.9%) ( Figs. 4 , 5 , Tables 1 , 2 ; Hata et al. 2020b: tables 2, 3).

Welch’s t -test for comparison of meristic characters between S. lotus and S. acinaces showed that p values of 8 and 4 characters in the pair were <0.01 and 0.1 <p <5, respectively, with no significant differences in other meristic characters ( Table 1 ). In addition, ANCOVA analysis of 35 morphometric characters showed significant differences (p <5) in 18 (head length, body depth, pre-dorsal-fin length, snout tip to pectoral-fin insertion, snout tip to pelvic-fin insertion, pre-anal-fin length, dorsal-fin base length, orbit diameter, snout length, distance between dorsal-fin origin to anal-fin origin, distance between insertions of pectoral and pelvic fins, pelvic-fin length, maxilla length, mandibular length, first dorsal-fin ray length, first anal-fin ray length in % SL and eye diameter and maxilla length in % HL) between S. lotus and S. acinaces ( Table 2 ).

Comparing S. lotus with S. andhraensis , Welch’s t -test for comparison of meristic characters between S. lotus and S. andhraensis showed that p values of 13 and 3 characters in the pair were <0.01 and 0.1 <p <5, respectively, with no significant differences in other meristic characters ( Table 1 ). Additionally, ANCOVA analysis of 35 morphometric characters showed significant differences (p <5) in 20 (head length, body depth, pre-dorsal-fin length, pre-anal-fin length, dorsal-fin base length, anal-fin base length, caudal-peduncle length, snout length, distance between dorsal-fin origin to anal-fin origin, distance between pelvic-fin insertion to anal-fin origin, maxilla length, mandibular length, distance between posterior ends of supramaxilla and maxilla, lengths of first dorsal, second, and third dorsal-fin rays and first anal-fin ray length in % SL and maxilla length, interorbital width and postorbital length in % HL) between S. lotus and S. andhraensis ( Table 2 ).

A PCA plotting graph of the three species of Stolephorus based on 29 morphological characters is shown in figure 6. PCA yielded six PCs (with eigenvalue> 1), responsible for 79.38% variation in the morphological data ( Table 5 ). PC1, PC2 and PC3 accounted for 24.89%, 15.27%, and 11.85% variation, respectively. The loading matrix on PC1, PC2, and PC3 identified 9 characters with high loading (> 0.3). These are head length, lower-jaw length, distance between origins of dorsal fin and anal fin, 1LGR, 1TGR, 2UGR, 3UGR, 3LGR, and 3TGR ( Table 6 ). The PC1 vs. PC1 plot unambiguously separated S. lotus from S. acinaces and S. andhraensis ( Fig. 6 ).

Figures

Fig. 1. (A) Lateral, (B) dorsal, and (C) ventral views of holotype of Stolephorus lotus sp. nov. (NTM S. 15265-006, 40.0 mm SL, Van Diemen Gulf, Northern Territory, Australia).

Fig. 2. Head of paratype of Stolephorus lotus sp. nov., NTM S. 15265-009, 36.2 mm SL, Van Diemen Gulf, Northern Territory, Australia. Dots indicate posterior part of maxilla. Triangle and arrow indicate cavity of preopercle and posterior tip of maxilla, respectively. Scale bar indicates 1 mm.

Fig. 3. Relationships of selected measurements relative to standard length (SL) or head length (HL) versus SL in Stolephorus lotus sp. nov. (circles) and S. acinaces (triangles). A, head length (as % of SL); B, predorsal fin length as % SL; C, body depth as % SL; D, maxilla length as % HL.

Fig. 4. Relationships of total gill raker numbers (TGR) on (A) first gill arch (1GA), (B) second gill arch (2GA) and (C) third gill arch (3GA) to SL in Stolephorus lotus sp. nov. (circles) and S. andhraensis (squares).

Fig. 5. Relationships of caudal-peduncle length to SL in Stolephorus lotus sp. nov. (circles) and S. andhraensis (squares).

Fig. 6. A principal components analysis (PCA) graph plotting the first two components for Stolephorus lotus sp. nov. (circles), S. acinaces (triangles), and S. andhraensis (squares) based on 29 morphological characters.