Squalus brevirostris Tanaka, 1917

Viana, Sarah T. F. L. & Carvalho, Marcelo R. de, 2020, Squalus shiraii sp. nov. (Squaliformes, Squalidae), a new species of dogfish shark from Japan with regional nominal species revisited, Zoosystematics and Evolution 96 (2), pp. 275-311 : 275

Squalus brevirostris Tanaka, 1917 Figs 3G, H , 5 , 7I, J , 8D ; Tables 4, 6 Japanese short-snout spurdog; Tsumari-aizam (Japanese)

Squalus brevirostris Tanaka 1917: 464-467, plates CXXIX and CXXX, figs 362-364 (original description, illustrated; type by original designation; type locality: Tokyo fish market, Japan, probably from Shimonoseki, Yamagueh Prefecture); Garrick 1960: 537 (cited; North-western Pacific Ocean); Zhu 1960: 106, 110-112 (description; Northwest Pacific Ocean); Chen et al. 1979: 26, 40 (cited; North-western Pacific Ocean); Zhu et al. 1984: 296 (cited; North-western Pacific Ocean); Siming et al. 1988: 1 (listed; Northwest Pacific Ocean); Nakabo 2002: 155 (listed; Ryukyu Islands, Japan); Duffy and Last 2007a: 31, 36, 37 (cited, North and Central Western Pacific Ocean); Ward et al. 2007: 116 (cited); Naylor et al. 2012: 58 (cited; North-western Pacific Ocean); Nakabo 2013: 195 (listed; Japan); Shinohara et al. 2014: 233 (listed; North-western Pacific Ocean).

Squalus megalops : Compagno 1984: 118-119 (cited; North-western Pacific Ocean); Zhu and Meng 2001: 311, 318-319 (cited, description; Northwest Pacific Ocean).

Type material.

ZUMT 7630 (holotype), adult male, 426 mm TL, collected at Tokyo fish market, Japan, unknown collecting date and collector.

Additional material.

CAS 15916, juvenile male, 380 mm TL, Formosa Strait, Taiwan, 26°N, 121°E, 90 m depth; CAS 30563, juvenile female, 270 mm TL, Formosa banks, Taiwan strait, Taiwan, 22°40'N, 118°30'E, 50 m depth; CSIRO H 6293-29, juvenile female, 404 mm TL, Tashi fish market, near I-Lan (NE coast), Taiwan; CSIRO H 6483-02, adult male, 450 mm TL, off Kasasa, Kagoshima, Japan, East China Sea, 31°29'N, 130°02'E, 145-150 m depth; HUMZ 33679, juvenile male, 390 mm TL, East China Sea, 29°54'N, 126°08'E; HUMZ 95065, adult female, 465 mm TL, East China Sea, 26°14.7'N, 124°42.5'E, 270-342 m depth; HUMZ 189743, adult male, 387 mm TL, East China Sea; HUMZ 189745, adult female, 450 mm TL, East China Sea; HUMZ 189747, adult male, 365 mm TL, East China Sea; HUMZ 189751, adult male, 395 mm TL, East China Sea; HUMZ 189756, adult female, 402 mm TL, East China Sea; HUMZ 189757, juvenile female, 357 mm TL, East China Sea; HUMZ 189758, adult female, 475 mm TL, East China Sea; HUMZ 189761, adult male, 400 mm TL, East China Sea; HUMZ 189762, adult male, 403 mm TL, East China Sea; HUMZ 189763, adult female, 433 mm TL, East China Sea; HUMZ 189767, juvenile male, 275 mm TL, East China Sea; KAUM-I 185, adult female, 500 mm TL, off Kasasa, Kagoshima, Japan, East China Sea, 31°29'N, 130°02'E, 145-150 m depth; KAUM-I 187, adult female, 578 mm TL, locality same as KAUM-I 185; KAUM-I 377, adult male, 377 mm TL, locality same as KAUM-I 185; NSMT-P 47378, adult female, 600 mm TL, Central Pacific Ocean; NSMT P-47379, adult male, 452 mm TL, Derwent-Hunter Guyot, 30°36.3'S, 156°12.2'E; NSMT-P 64979, two juvenile females, 480-520 mm TL, East China Sea, 29°0.57'N, 127°0.4'E, 167-170 m depth; SU 13468, adult female, 530 mm TL, Osaka market, Japan, 34.70N, 135.49E; SU 230373, neonate female, 270 mm TL, two neonate males, 200 mm TL, South China Sea, 19°6'30"N, 112°38'00"E, 111-119 m depth; ZUMT uncatalogued, female embryo, 147 mm TL, male embryo, 182 mm TL, Japan.

Diagnosis.

A small-sized (373-578 mm TL in adults) Squalus species that differs from its Japanese congeners by: snout conspicuously short, its prenarial length 4.0%, 3.8%-4.3% TL (vs. 5.4%-5.6% TL for S. shiraii sp. nov. vs. 4.1%-5.6% TL for S. mitsukurii vs. 5.9%-6.8% TL for S. japonicus vs. 4.7%-5.1% TL for S. acutirostris ); dermal denticles unicuspid and lanceolate; pectoral-fin free rear tips conspicuously pointed; more elongate pectoral fins with its inner margin length 10.3%, 9.8%-11.2% TL (vs. 7.3%-8.3%TL for S. shiraii sp. nov. vs. 7.7%-9.5% TL for S. mitsukurii vs. 7.5%-8.8% TL for S. japonicus vs. 7.3%-8.7% TL for S. suckleyi vs. 6.6%-8.3% TL for S. acutirostris ). It is further separated from S. japonicus and S. shiraii sp. nov. by narrower internarial space (3.6%, 3.4%-3.8% TL vs. 4.1%, 4.1%-4.7% TL for S. japonicus vs. 4.8%, 4.1%-4.8% TL for S. shiraii sp. nov.) and from S. shiraii sp. nov. by larger second dorsal and pelvic fins (second dorsal-fin inner margin length 5.0%, 4.8%-5.7% TL and pelvic fin length 11.7%, 10.9%-13.6% TL vs. 3.6%, 3.2%-4.1% TL and 10.7%, 9.5%-10.7% TL for S. shiraii sp. nov.) and wider caudal fin, its width at caudal fork 6.6%, 6.6%-7.3% TL (vs. 6.4%, 5.7%-6.4% TL for S. shiraii sp. nov.). It is distinct from S. japonicus by snout rounded at tip, shorter preorbital (6.7%, 6.5%-7.5% TL vs. 8.7%, 8.7%-10.3% TL for S. japonicus ) and preoral length (9.1%, 8.4%-9.5% TL vs. 10.7%, 10.7%-12.2% TL for S. japonicus ). Squalus brevirostris is easily separated from S. mitsukurii and S. shiraii sp. nov. by mononspondylous and total vertebrae (40, 37-42 and 110, 105-114 vs. 44-46 and 116-117 for S. mitsukurii vs. 47, 44-48 and 122, 120-123 for S. shiraii sp. nov.). It also exhibits lower number of precaudal vertebrae than S. shiraii sp. nov. (83, 78-89 vs. 93, 91-94 for S. shiraii sp. nov.).

Description.

External morphology. Small size species (147.0-578.0 mm TL) of Japanese dogfish. Body fusiform and slender, equally deep from head to trunk (head height 0.9, 0.9-1.0 times trunk height and 1.0, 0.8-1.2 times abdomen height) (Fig. 5A-C ). Head very short, its length 21.9% (20.0%-29.6%) TL; head width 1.4 (1.0-1.4) times broader than trunk width and 1.1 (1.1-1.6) times abdomen width. Snout somewhat obtuse ventrally, very short (preorbital length 6.7%, 6.5%-7.5% TL); anterior nasal flap broad and bifurcated, nearer to snout tip than to mouth with prenarial length 0.8 (0.8-0.9) times distance from nostril to upper labial furrow (Fig. 5D-F ). Eyes oval with anterior margin rounded and posterior margin notched; eyes large, its length 2.3 (1.8-2.5) times its height. Prespiracular length 0.6 (0.5-0.6) times prepectoral length and 1.8 (1.6-1.9) times preorbital length. Spiracle crescent and narrow, its length 0.3 (0.3-0.4) times eye length, nearer to posterior margin of the eye than to first gill slit. First and fifth gill slits somewhat concave and low; fifth gill slit 1.1 (0.9-1.6) times higher than first gill slit.

Preoral length somewhat equal to mouth width, corresponding to 1.1 (1.1-1.2) times the latter. Mouth markedly arched and narrow, its width 2.3 (1.8-2.3) times broader than internarial space; upper labial furrow small, its length 2.6% (2.0%-2.7% TL) with thin fold; lower labial furrow also short with fold subdivided into three small inter-digits. Teeth tiny and unicuspid, labial-lingually flattened and alternate, similar in both jaws, lower teeth slightly wider than the upper teeth; cusp short and oblique; mesial cutting edge convex; both distal and mesial heels rounded; apron elongate in upper and lower teeth (Fig. 3G, H ). Three and two series of functional teeth on upper and lower jaws for holotype (two series for non-type specimens); 12-0-13 (12-0-12) teeth rows in upper jaw; 10-0-10 (10-0-10) teeth rows in lower jaw.

Pre-first dorsal length 1.4 (1.3-1.6) times prepectoral length. First dorsal fin short, its length 1.7 (1.5-1.9) times its height; first dorsal-fin low, its height 1.3 (1.2-1.5) times greater than its inner margin length; first dorsal-fin anterior margin concave and posterior margin straight; first dorsal-fin free, rear tip pointed; first dorsal-fin apex rounded and slender at fin web (Fig. 5G, K ). Origin of first dorsal-fin spine anterior to vertical traced at free rear tips of pectoral fins; first dorsal-fin spine short (broken in the holotype), never reaching first dorsal-fin apex, its length 0.3-0.6 times first dorsal-fin height. Interdorsal space 1.1 (1.1-1.3) times prepectoral length and 2.4 (2.2-2.6) times larger than dorsal-caudal space. Pre-second dorsal length 2.8 (2.7-3.3) times greater than prepectoral length and 3.0 (2.8-3.2) times the length of dorsal caudal margin. Second dorsal fin very short, its length 0.9 (0.8-1.0) times first dorsal-fin length; second dorsal fin low, its height 1.2 (0.8-1.4) times length of second dorsal-fin inner margin; second dorsal-fin anterior margin concave and posterior margin markedly falcate; second dorsal-fin apex rounded and evidently slender at fin web (Fig. 5H, L ). Second dorsal-fin spine thick and elongate, although not reaching the apex, its length 0.8 (0.8-1.1) times the fin height; second dorsal-fin spine length 1.3-2.6 times greater than length of first dorsal-fin spine.

Pectoral fin conspicuously narrow with pectoral-fin anterior margin length 1.4 (1.3-1.9) times larger than pectoral-fin posterior margin length and 1.4 (1.1-1.5) times larger than pectoral-fin inner margin length; pectoral-fin anterior and inner margins convex; pectoral-fin posterior margin conspicuously concave; pectoral-fin apex rounded and lobe-like; pectoral-fin free rear tips markedly pointed and triangular, markedly lobe-like (Fig. 5I, M ); pectoral-fin free rear tips reaching the horizontal line traced at pectoral-fin apex. Pectoral-pelvic space 0.8 (0.6-0.9) times pelvic-caudal space. Pelvic fins nearer to first dorsal fin than second dorsal fin. Pelvic fins very narrow with pelvic-fin margins straight; pelvic-fin apex rounded; pelvic-fin free rear tips triangular, pointed and lobe-like; pelvic fin length 1.2 (0.9-1.2) times length of preventral caudal margin. Clasper flattened ventrally and small, its outer length 3.9% (1.4%-5.1% TL), transcending the pelvic-fin free rear tips; clasper groove dorsal, longitudinal and short; apopyle and hypopyle with conspicuous apertures, near each other; rhipidion blade-like, located at the posterior end of the clasper; inner length of clasper 1.2 (0.5-1.2) times length of pelvic-fin inner margin.

Caudal keel prominent, reaching from forward second dorsal fin insertion to behind origin of caudal fin. Caudal fin slightly slender in the dorsal caudal lobe; dorsal caudal and upper postventral caudal margins convex; dorsal caudal tip rounded (Fig. 5J, N ); dorsal caudal margin 0.9 (0.7-1.0) times head length and 2.0 (1.5-2.0) times larger than preventral caudal margin; lower postventral caudal margin convex (broken in holotype); preventral caudal margin strongly convex and short, its length 1.7 (1.6-2.3) times greater than length of pelvic-fin inner margin; ventral caudal tip rounded (broken in holotype); caudal fork discontinuous between lobes, its width 6.6% (6.6%-7.6%) TL.

Squamation (Fig. 7I, J ). Dermal denticles unicuspid and lanceolate, not imbricated; cusp rounded and posterior; denticles conspicuously slender at crown, although markedly broad medial-anteriorly at its base; denticles with length much greater than its width; median ridge tall and thick, bifurcated anteriorly with profound anterior furrow; lateral ridges tall and thin, shorter than median ridge.

Colouration (Fig. 5 ). Body brownish-grey dorsally, white ventrally and latero-posteriorly Pectoral fins grey with pectoral-fin posterior and inner margins white. Pelvic fins white dorsally and ventrally. First dorsal fin brownish-grey, slightly white at first dorsal-fin posterior margin, free rear tip and fin base; second dorsal fin light brown, whitish at the fin base, somewhat white at second dorsal-fin apex, posterior margin and freer rear tip. Dorsal-fin spines grey, dark grey anteriorly and white at the tip. Caudal fin light brown, whitish near vertebral column; postventral caudal margins white, broadly white at dorsal caudal tip and from ventral caudal tip to caudal fork; light black caudal stripe.

Vertebral counts (Table 6 ). 83 (holotype) 78-89 (other material) precaudal vertebrae; 70 (66-72) diplospondylous vertebrae; 110 (105-114) total vertebrae.

Geographical distribution.

This species occurs in tropical and subtropical areas of the North-western Pacific Ocean from Southern Japan, China and Taiwan on continental shelves and upper continental slopes between 50-342 m depth (Fig. 8D ). It is also recorded from the Philippines in Manjaji-Matsumoto (2017).

Remarks.

Morphological variations in the shape of pectoral and dorsal fins, dermal denticles and colour of caudal fin are observed within S. brevirostris . First dorsal-fin posterior margin is somewhat straight near its apex like in the holotype, although other specimens exhibit first dorsal-fin posterior margin concave. Pectoral fins are slightly broad at posterior margin in specimens from the Central Western Pacific Ocean (except Taiwan), while it is narrow in others like that observed for the holotype. Pelvic fins are nearer to first dorsal fin, although it may be in the midline between the two dorsal fins in a few specimens. Caudal fin has postventral caudal margins white, although narrowly white at caudal fork in specimens from Kagoshima. Thickness of the dermal denticles varies from very slender to conspicuously broad at the crown in few specimens from Kagoshima. These variations are possibly not related to dimorphism or ontogeny and apparently it is scattered, as it has an unclear morphological pattern throughout the distributional range of this species in the North and Central Western Pacific Ocean. Duffy and Last (2007a) previously noticed differences in the dermal denticles, which was suggested to be due to ontogeny. Further comparative investigations are required to include more specimens from Taiwan and South Korea in order to better understand these variations within the species.

Squalus brevirostris exhibits low vertebral counts that are usually overlapped to those of morphologically similar species occurring elsewhere, such as S. megalops , S. acutipinnis and S. lobularis . However, it can be separated from other similar species by precaudal vertebrae with S. hemipinnis , S. notocaudatus and S. formosus , total vertebrae with S. hemipinnis , S. notocaudatus , S. formosus and S. albifrons and monospondylous vertebrae with S. notocaudatus , S. formosus , S. albifrons and S. bucephalus .

Figures

Figure 3. Upper (A, C, E, G, I) and lower (B, D, F, H, J) teeth of S. shiraii sp. nov. (A, B; HUMZ 80329), S. mitsukurii (C, D; HUMZ 33680), S. japonicus (E, F; HUMZ 189737), S. brevirostris (G, H; HUMZ 189762) and S. suckleyi (I, J; NSMT-P 92640). Scale bars: 1 mm.

Figure 5. Squalus brevirostris: lateral (A-C) and ventral (D-F) views; first (G, K) and second (H, L) dorsal fins; pectoral (I, M) and caudal (J, N) fins. ZUMT 7630 (holotype), adult male, 426 mm TL (A, D, G-J); HUMZ 189762, adult male, 403 mm TL (B, E, K-N); HUMZ 189767, juvenile male, 275 mm TL (C, F). Scale bars: 50 mm (A-F); 20 mm (G-N).

Figure 7. Scanning electron microscopy of the dermal denticles. Squalus shiraii sp. nov. (A, B): HUMZ 149389 (holotype), adult male, 590 mm TL. S. formosus (C, D): CSIRO H- 6816 - 01 (holotype), adult male, 720 mm TL. S. mitsukurii (E, F): HUMZ 102987, adult male, 970 mm TL. S. japonicus (G, H): NSMT-P 44380 (neotype), adult male, 645 mm TL (G); NSMT-P 91127, juvenile female, 410 mm TL (H). S. brevirostris (I, J): NSMT-P 47378, adult female, 600 mm TL (I); KAUM-I 187, adult female, 578 mm TL (J). S. suckleyi (K, L): NSMT P- 92640, adult female, 970 mm TL. Scale bars: 50 μm (B); 100 μm (D, F, L); 200 μm (A, C, E, G-K).

Figure 8. Map of the North-western Pacific Ocean, showing the geographical distribution of Squalus species. A: S. shiraii sp. nov. (red); B: S. mitsukurii (orange); C: S. japonicus (brown); D: S. brevirostris (yellow); E: S. acutirostris (green); F: S. suckleyi (pink). Star: holotype / neotype; Dotted circle: paratypes; Circle: other material.