Halaleurus immaculatus Chu & Meng, 1982

White, William T. & Last, Peter R., 2013, Notes on shark and ray types at the South China Sea Fisheries Research Institute (SCSFRI) in Guangzhou, China, Zootaxa 3752 (1), pp. 228-248 : 237

Halaleurus immaculatus Chu & Meng, 1982

[= Bythaelurus immaculatus ( Chu & Meng, 1982) ]

( Figures 12–13 )

Halaelurus immaculatus Chu & Meng in Chu, Meng, Hu & Li, 1982: 301, fig. 1 (South China Sea) – Compagno, 1984: 326, figs.

Halaelurus (Bythaelurus) immaculatus – Compagno, 1988: 146.

Bythaelurus immaculatus – Compagno et al., 2005a: 214, fig., pl. 35; Last & Stevens, 2008: 123.

Material examined. SCSFRI O 0094 (holotype), adult male ~ 708 mm TL, South China Sea, 19°24.8' N, 114°23.6' E, depth 1020 m, 6 Oct 1980 .

Remarks. Originally described as Halaelurus immaculatus by Chu & Meng in Chu et al. (1982) based on three specimens collected in the South China Sea. Allocated to the genus Bythaelurus Compagno, 1988 , which was previously a subgenus of Halaelurus . This genus is distinguishable from Halaleurus in the following combination of characters: snout bluntly rounded (vs. pointed); eyes not elevated on dorsal surface of head (vs. noticeably elevated on dorsal head); skin thin and body soft (vs. skin thick and body firm); and typically uniformly brownish, grey or blackish (vs. light grey or brown with a bold colour pattern of stripes, bands or spots) ( Compagno, 1988). Specimens of B. immaculatus were not examined by Compagno (1984, 1988) but he did note that it is a close relative of the New Zealand endemic Bythaelurus dawsoni ( Springer, 1971) . Chu & Meng in Chu et al. (1982) did not discuss how B. immaculatus differs from B. dawsoni , but they differ in the following characters: anal-fin base about 1.4 times in interdorsal space (vs. subequal to interdorsal space in B. dawsoni ), body uniformly dark yellowish brown (vs. light brown to grey on dorsal and lateral surfaces with a line of white spots on sides of small individuals, whitish ventrally), and caudal fin uniformly dark (vs. light brown to grey with dark bands).

The anal-fin base is subequal in length to the second dorsal-fin base, which as noted by Chu & Meng in Chu et al. (1982) clearly distinguishes this species from B. hispidus ( Alcock, 1891) and B. lutarius ( Springer & D'Aubrey, 1972) in which the anal-fin base is about twice the length of the second dorsal-fin base. Of the remaining Bythaelurus species , B. immaculatus is most similar in appearance to B. canescens ( Günther, 1878) from the Eastern Pacific and Bythaelurus incanus Last & Stevens, 2008 from northwestern Australia. Bythaelurus incanus differs from B. immaculatus in having a shorter prevent length (more than 1.3 in tail length vs. exceeding tail length), shorter interdorsal space (about 1.7 times first dorsal-fin base vs. more than 2.2 times), and pectoralpelvic space 1.7 times interdorsal space (vs. ~2.4 times) ( Last & Stevens, 2008 vs. holotype of B. immaculatus ). Bythaelurus canescens differs from B. immaculatus in being a more robust shark with a deeper and broader head and trunk, and a less broadly rounded snout (vs. broadly rounded). Chu & Meng in Chu et al. (1982) provided additional differences between these two species, including pectoral-pelvic space 2.4-2.5 times interdorsal space in B. immaculatus (vs. 1.5 times in B. canescens ). However, estimates of this ratio by the author from images of B. canescens from off Chile were much higher, i.e. about 2 times. This is still likely to be a useful character but it possibly varies between specimens so caution should be taken.

Thus, Bythaelurus immaculatus clearly differs from all of its congeners and should be considered a valid species of Bythaelurus . This species has not been recorded since the 1982 description based on three specimens collected in 1980 in the South China Sea. More deepwater trawling may reveal this species has a broader distribution in this region, but alternatively it may be a narrow-ranging endemic.

Figures

FIGURE 12. Lateral view of the holotype of Bythaelurus immaculatus SCSFRI O 0094 (adult male ~708 mm TL).

FIGURE 13. Ventral head view of the holotype of Bythaelurus immaculatus SCSFRI O 0094 (adult male ~708 mm TL).