Narrowhead Catshark

description

Description of holotype (Figures 3 – 11). Values of the paratype are given in parentheses if differing. Morphometric measurements and meristics are given in Table 1. External morphology. Body firm and elongated, subcircular in cross section at mid-trunk, laterally compressed and tapering posterior to anus; head region slender, long abdominal and caudal sections (Figures 3 – 5). No predorsal, interdorsal, or postdorsal ridges; no postanal ridge; no lateral ridges. Trunk slightly shorter than tail, distance from tip of snout to anterior cloaca 46.2 % (42.9 %) TL; pre-first dorsal-fin length 48.3 % (46.1 %) TL, presecond dorsal-fin length 63.3 % (63.2 %) TL, precaudal length 71.3 % (68.6 %) TL. Head slender and with a broadly pointed snout; laterally slightly compressed in gill region (Figures 6 – 7); no supraorbital crest on chondrocranium; head length 3.1 (2.7) times width at level of maximum extent of anterior nostrils and 1.3 (1.2) times pectoral-pelvic space; head width at level of maximum outer extent of anterior nostrils only 1.2 times width at level of lateral indention of head, equal to preorbital length, and 7.2 % (7.3 %) TL; head width at posterior edge of nostrils 1.4 and

Bythaelurus tenuicephalus n. sp., a new deep-water catshark (Carcharhiniformes, Scyliorhinidae) from the western Indian Ocean

diagnosis

Diagnosis. A very small scyliorhinid species with the following characteristics: body firm and elongated; snout long (preorbital length 6.7 – 7.1 % TL) and slender, only slightly bell-shaped in dorsoventral view without distinct lateral indention; pre-outer nostril length 1.2 times internarial space; preorbital snout length 1.0 – 1.4 times interorbital space; preoral snout length 1.3 – 1.4 times in mouth width; eye length 14.0 – 15.3 times in predorsal distance, 6.0 – 7.0 times in head length and 1.7 – 1.8 times eye height; head length 2.7 – 3.1 times width at level of maximum outer extent of anterior nostrils; head width at level of maximum outer extent of anterior nostrils only 1.2 times width at level of lateral indention of head, equal to preorbital length, and 7.2 – 7.3 % TL; tongue and roof of mouth loosely set with oral papillae of distinct size; pelvic anterior margin 1.9 – 2.1 times in pectoral fin anterior margin; first dorsal fin base 1.9 times in interdorsal space; length of second dorsal fin inner margin 1.4 times in second dorsal fin height; second dorsal-fin base length 5.9 – 6.9 % TL; anal-fin base 0.9 – 1.1 times interdorsal space. Coloration in preservative: bicol

Bythaelurus tenuicephalus n. sp., a new deep-water catshark (Carcharhiniformes, Scyliorhinidae) from the western Indian Ocean

discussion

Remarks. Bythaelurus tenuicephalus n. sp. is easily distinguished from its congeners based on the narrow shape of its head and snout, which is only slightly bell-shaped in dorsoventral view without distinct lateral indention. All other Bythaelurus species have distinctly bell-shaped heads with strong lateral indention anterior to outer nostrils. The coloration of Bythaelurus tenuicephalus also clearly distinguishes it from B. clevai (Figure 12 A) due to having a color pattern of fewer and smaller blotches. Furthermore, B. tenuicephalus differs from B. clevai by attaining a smaller maximum size (about 30 cm TL vs. 39 cm TL according to Weigmann, in press), having larger papillae on tongue and especially roof of mouth, a smaller ratio eye length in predorsal space (14.0 – 15.3 vs. 16.7 times in the adult male ZMH 26071 of B. clevai), a smaller ratio pre-outer nostril length times internarial length (1.2 vs. 1.5), a shorter snout (preorbital length 6.7 – 7.1 % TL vs. 8.3 % TL, preoral length 5.5 – 5.7 % vs. 7.0 % TL), a shorter pectoral-pelvic space (16.4 – 16.6 % TL vs. 19.7 % TL), and broader claspers in adults (base width 2.1 % TL vs. 1.8 % TL). Additionally, the tip of the clasper

Bythaelurus tenuicephalus n. sp., a new deep-water catshark (Carcharhiniformes, Scyliorhinidae) from the western Indian Ocean

distribution

Distribution. Known from the upper slope off northern Tanzania in the Pemba Channel between Zanzibar and Pemba Island, 5 ° 27.9 ’ S, 39 ° 18.8 ’ E, in 463 m depth and from off southern Mozambique, 21 ° 12 ' 8 " S, 35 ° 41 ' 8 " E – 21 ° 16 ' 6 " S, 35 ° 41 ' 3 " E, in 490 – 550 m depth.

Bythaelurus tenuicephalus n. sp., a new deep-water catshark (Carcharhiniformes, Scyliorhinidae) from the western Indian Ocean