Monday, June 15, 2020

[Ichthyology • 2020] Squalus shiraii • A New Species of Dogfish Shark (Squaliformes, Squalidae) from Japan with Regional Nominal Species Revisited

Squalus shiraii 
Viana & Carvalho, 2020

 Shirai’s Spurdog  ||  DOI: 10.3897/zse.96.51962 

A new species of deep-water dogfish shark, Squalus shiraii sp. nov., is described herein as endemic to the tropical waters off Southern Japan. This species has been largely misidentified with S. mitsukurii. However, morphological, meristic and morphometric evidence support it to be a separate and undescribed species. Squalus shiraii sp. nov. differs from this species by having body brown in colour dorsally, caudal fin with ventral and dorsal tips markedly tapered and broadly white, dermal denticles uniscuspidate and lanceolate and larger number of precaudal (91–94) and total vertebrae (120–123) (vs. body dark grey to black; caudal fin with ventral and dorsal tips rounded and not white in colour; denticles tricuspidate and rhomboid; 86–90 precaudal and 116–117 total vertebrae). Squalus shiraii sp. nov. is also clearly separated from other Japanese congeners which are herein revisited to include six species, based on the examination of over 150 specimens caught from Japanese waters that were available in ichthyological collections: S. mitsukurii, S. japonicus, S. acutirostris, S. brevirostris and S. suckleyi. Squalus mitsukurii, S. japonicus and S. brevirostris are re-described in detail and the neotype of S. japonicus is herein designated. Squalus acutirostris is treated as a valid species with occurrences in Japan, China and Taiwan and, thus, a provisional diagnosis is given, as well as an updated diagnosis of S. suckleyi. A key to Squalus species from the North-western Pacific Ocean is given and main morphological differences between S. shiraii sp. nov. and the closest related species are discussed.

Key Words: taxonomy, species diversity, elasmobranch, Squalus, North-western Pacific Ocean

Figure 1. Squalus shiraii sp. nov.: lateral (A–C) and ventral (D, E) views; first (F) and second (G) dorsal fins; pectoral (H) and caudal (I) fins.
HUMZ 149389 (holotype), adult male, 590 mm TL (A, D, F–I); HUMZ 80329 (paratype),
adult female, 770 mm TL (B); HUMZ 80330 (paratype),
juvenile male, 365 mm TL (C, E). Scale bars: 50 mm (A–E); 20 mm (F–I).


Squalus shiraii sp. nov.

Diagnosis: Single values correspond to the holotype and range to paratypes, respectively. A Squalus species that is separated from its regional congeners by: first dorsal fin conspicuously upright (vs. first dorsal fin prone); pectoral-fin posterior margin falcate (vs. not falcate); upper and lower caudal lobes markedly slender with dorsal and ventral caudal tips pointed and broadly white (vs. upper and lower caudal lobes wide with dorsal and ventral caudal tips rounded and greyish in colour); dermal denticles lanceolate, except for S. brevirostris (vs. tricuspidate); smaller claspers with clasper outer length 3.3%, 3.3%–3.4% TL and clasper inner length 6.3%, 5.9%–6.3% TL (vs. 4.5%–4.9% TL, 6.9%–8.4% TL for S. mitsukurii vs. 4.8%, 4.3%–5.6% TL and 7.5%, 7.2%–9.1% TL for S. japonicus; vs. 3.9%, 3.9%–5.1% TL and 7.1%, 7.0%–8.1% TL for S. brevirostris). Squalus shiraii sp. nov. further differentiates from S. mitsukurii by more elongate eyes, its length 4.9%, 4.4%–4.9% TL (vs. 3.6%, 3.1%–4.0% TL) and smaller fifth gill slit, its length 1.7%, 1.7%–2.1% TL (vs. 2.3%, 2.2%–2.6% TL). It is separated from S. japonicus and S. brevirostris by prenarial length 5.5%, 5.4%–5.6% TL (vs. 5.9%, 5.9%–6.8% TL for S. japonicus vs. 4.0%, 3.8%–4.3% TL for S. brevirostris) and width of first dorsal-fin spine 0.9%, 0.9%–0.9% TL (vs. 0.7%, 0.5%–0.8% TL for S. japonicus vs. 0.7%, 0.5%–0.7% TL for S. brevirostris). Squalus shiraii sp. nov. further differs from S. japonicus by shorter snout, its preorbital length 7.9%, 7.4%–7.9% TL (vs. 8.7%, 8.7%–9.3% TL for S. japonicus), smaller preoral length 10.4%, 9.4%–10.4% TL (vs. 10.7%, 10.7%–12.2% TL), larger first dorsal fin, its base length 7.7%, 7.7%–8.7% TL and first dorsal-fin posterior margin length 9.2%, 9.0%–9.3% TL (vs. 6.7%, 6.6%–7.5% TL and 7.8%, 6.7%–8.6% TL for S. japonicus) and wider pectoral fin, its posterior margin length 10.0%, 10.0%–11.7% TL (vs. 8.6%, 7.8%–9.2% TL). It is separated from S. brevirostris by wider internarial space, its width 4.8%, 4.1%–4.8% TL (vs. 3.6%, 3.4%–3.8% TL for S. brevirostris), smaller second dorsal fin with inner margin length 3.6%, 3.2%–4.1% TL (vs. 5.0%, 4.8%–5.7% TL), shorter pectoral-fin inner margin, its length 7.3%, 7.3%–8.3% TL (vs. 10.3%, 9.8%–11.2% TL) and narrower caudal fin, its width at caudal fork 6.4%, 5.7%–6.4% TL (vs. 6.6%, 6.6%–7.3% TL). Squalus shiraii is distinguished from S. formosus regardless of maturity by having more elongate precaudal (78.3%, 78.6%–80.5% TL), pre-second (60.5%, 61.1%–63.4% TL) and pre-first (30.5%, 29.6%–31.2% TL) dorsal length (vs. 77.6%–78.3% TL, 59.4%–59.7% TL and 28.1%–29.0% in S. formosus).

Etymology: This species is named after Dr. Shigeru M. Shirai, Japanese ichthyologist from Tokyo University of Agriculture, for his valuable contributions to Systematics of Squaliformes.

Vernacular: Shirai’s Spurdog; Hiretaka-tsunozame (Japanese).

Geographical distribution: This species is apparently a Japanese endemic, occurring in the shallow waters of the upper continental slope off Southern Japan in the North-western Pacific Ocean at 310–390 m depth (Fig. 8A).

 Sarah T. F. L. Viana and Marcelo R. de Carvalho. 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): 275-311. DOI: 10.3897/zse.96.51962