Squalus acutirostris Zhu, Meng & Li, 1984

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 acutirostris Zhu, Meng & Li, 1984 Figs 6A-E , 8E ; Table 2 Shortspine spurdog

Squalus acutirostris Zhu, Meng and Li 1984: 283-286, fig.1 (original description; illustrated; type by original designation; type locality: South China Sea, 18°51'-18°47'N, 112°41'-112°33'E, 394 m depth).

Squalus mitsukurii : White and Last 2013: 229-230 (cited, illustrated; Taiwan); Motomura et al. 2015: 12-13 (cited, listed, illustrated; Uji Islands, East China Sea); Weigmann 2016: 904 (cited; Western Pacific Ocean).

S. japonicus : Quang et al. 2013: 22, 27-28 (cited, listed, illustrated; Quy Nhon Bay, Vietnam).

Type material.

SCSFRI D01562 (holotype), adult male, 635 mm TL, South China Sea, 18°51'-18°47'N, 112°41'-112°33'E, 394 m depth, collected on 21 April 1982; SCSFRI D01548 (paratype), adult female, 975 mm TL, South China Sea, 18°50.8'-19°28.8'N, 112°47.3'-113°58.8'E.

Additional material.

HUMZ 74990, juvenile female, 536 mm TL, Kyushu-Palau Ridge, 26°14.1'-26°10.1'N, 135°47.5'-135°48.0'E, 360 m depth; NMMB P 15619 (photo only), adult female, 700 mm TL, Pingtung county, Taiwan.

Diagnosis.

Single values correspond to holotype first followed by a single paratype and a specimen from Japan between brackets. Squalus acutirostris is separated from its congeners by a combination of characters: large sized species (635-975 mm maximum TL in adults) with body moderately slender and fusiform (Fig. 6A ), its greatest width at head (head width 1.4(1.4, 1.2) times trunk width and 1.3(1.1, 1.2) times abdomen width); head small, its length 24.4%(22.6%, 22.1%) TL; snout rounded at tip and short, preorbital length 8.2%(7.3%, 8.1%) TL; nostrils nearer to snout than to mouth (Fig. 6B ); first dorsal fin oblique, wide at fin web and low, its height 6.0%(5.6%, 8.6%) TL; first dorsal fin concave at the lower half of posterior margin, not raked (Fig. 6C ); second dorsal fin with raked posterior margin (Fig. 6D ); dorsal-fin spines robust and short, never reaching the fin apex (first dorsal-fin spine length 2.8%(2.7%, 3.2%)TL; second dorsal-fin spine length 2.8%(1.9%, 4.8%) TL; pectoral fins moderately wide with posterior margin length 11.0%(10.3%, 10.1%) TL; pectoral-fin posterior margin concave, although not falcate; pectoral-fin free rear tips rounded; caudal fin rectangular with conspicuous caudal fork (Fig. 6E ); caudal fin small with dorsal caudal margin length 0.7(0.9, 1.0) times head length; lower caudal lobe much shorter than upper caudal lobe (preventral caudal margin length 0.7(0.6, 0.5) times dorsal caudal margin length); body brownish-grey to dark grey dorsally and light brown ventrally; first and second dorsal-fin apex slightly black; conspicuous black upper caudal blotch and small black caudal bar; black basal marking conspicuous at the origin of caudal fin; lower caudal lobe mostly white.

Geographical distribution.

Squalus acutirostris occurs in the North-western Pacific Ocean with reports from Japan, Taiwan and China (Fig. 8E ). It has been previously misidentified with S. japonicus in Vietnam as seen in Quang et al. (2013). It inhabits continental slopes between 360-525 m depth ( Zhu et al. 1984; present study).

Remarks.

Squalus acutirostris , originally described from the South China Sea, was previously recognised in China and Western Australia in Zhu et al. (1984), Muñoz-Chápuli and Ramos (1989) and Zhu and Meng (2001). White and Last (2013) have proven that the Australian records correspond to a distinct species, S. grahami White, Last & Stevens, 2007. Furthermore, occurrence of S. acutirostris in the South China Sea was thought to be related to S. mitsukurii ( White and Last 2013; Weigmann 2016) due to no apparent morphological and meristic distinction and, thus, this species was designated as a junior synonym. According to White and Last (2013), the differences in external measurements (e.g. precaudal length, interdorsal space, dorsal caudal margin length) between these species were due to the preservation condition of the holotype of S. acutirostris . However, the present analysis reveals many morphometric differences when adults are compared, such as: inner nostril-labial furrow space (6.9%-8.6% TL vs. 3.9%-4.5% TL for S. mitsukurii ); first dorsal fin height (5.6%-6.0% TL vs. 6.9%-9.8% TL for S. mitsukurii ); second dorsal-fin anterior margin length (6.8%-7.6% TL vs. 7.7%-10.2% TL for S. mitsukurii ); second dorsal-fin base length (4.8%-5.8% TL vs. 6.8%-7.9% TL for S. mitsukurii ); second dorsal fin height (3.3%-3.6% TL vs. 4.5%-6.8% TL for S. mitsukurii ); second dorsal-fin spine length and base width (1.9%-2.8% TL, 0.5%-0.6% TL vs. 3.4%-5.3% TL, 0.7%-1.0% TL for S. mitsukurii ). Further distinctive characteristics between S. mitsukurii and the types of S. acutirostris include conspicuously shorter snout with nostrils clearly nearer to the snout tip than to the mouth, its prenarial length 0.6-0.8 times nostril-labial furrow space (vs. elongate snout with nostrils nearer to the mouth, its prenarial length 1.1-1.4 times nostril-labial furrow space in S. mitsukurii ) and narrower pectoral and pelvic fins (vs. conspicuously broad pectoral and pelvic fins in S. mitsukurii ). These characteristics are congruent with observations of Zhu et al. (1984) and Zhu and Meng (2001) and are apparent, regardless of the preservation condition and which support the distinction between S. mitsukurii and the nominal species S. acutirostris .

Squalus acutirostris may be separated from the Japanese congeners by having more elongate second dorsal-fin length 63.9%-64.0% TL (vs. 60.5%-63.4% TL for S. shiraii sp. nov. vs. 58.4%-63.9% TL for S. mitsukurii vs. 60.7%-62.0% TL for S. japonicus vs. 61.1%-63.8% TL for S. brevirostris vs. 56.2%-62.3% TL for S. suckleyi ) and larger inner nostril-labial furrow space 6.9%-8.6% TL (vs. 4.3%-4.9% TL for S. shiraii sp. nov. vs. 3.9%-4.5% TL for S. mitsukurii vs. 4.6%-5.1% TL for S. japonicus vs. 4.5%-5.1% TL for S. brevirostris vs. 3.9%-5.6% TL for S. suckleyi ). It may also be distinguished from S. shiraii sp. nov., S. japonicus and S. brevirostris by pre-pelvic length 47.2%-49.3% TL and prenarial length 4.7%-5.1% TL (vs. 44.1%-46.8% TL and 5.4%-5.6% TL for S. shiraii vs. 43.7%-45.9% TL and 5.9%-6.8% TL for S. japonicus vs. 42.4%-46.9% TL and 3.8%-4.3% TL for S. brevirostris ). It is also easily separated from S. brevirostris by having pectoral free rear tips rounded (vs. conspicuously pointed).

Figures

Figure 6. Squalus acutirostris (A-E): HUMZ 74990, juvenile female, 536 mm TL in lateral (A) and ventral (B) views; first (C) and second (D) dorsal fins and caudal fin (E). S. suckleyi in lateral view (F): HUMZ 90963, adult female, 784 mm TL. Scale bars: 50 mm (A, B, F); 20 mm (C-E).

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.