Vivaldi's Catshark

description

Description of the holotype (Figures 2 – 10). Values of the paratype in parentheses if differing. Morphometric measurements and meristics are given in Table 1. B. vivaldii n. sp. B. vivaldii n. sp. presumably presumably adult female immature female paratype holotype ZMB 17410 ZMB 22423 B. vivaldii n. sp. B. vivaldii n. sp. presumably presumably adult female immature female paratype holotype ZMB 17410 ZMB 22423 B. vivaldii n. sp. B. vivaldii n. sp. presumably presumably adult female immature female paratype holotype ZMB 17410 ZMB 22423 External morphology. Body firm and stout with trunk width 11.0 % TL (rather slender with trunk width 9.4 % TL in presumably juvenile paratype), subcircular in cross section at mid-trunk, laterally compressed and tapering posterior to cloaca; head region broad, long abdominal and caudal sections (Figures 2 – 4). No predorsal, interdorsal, or postdorsal ridges; no postanal ridge; no lateral ridges on caudal peduncle. Trunk slightly shorter than tail, distance from tip of snout to anterior cloaca 45.8 % (44.8 %) TL; pre-first dorsal fin length 48.2 % (49.6 %) TL, pre-second dorsal fin length 67.0 % (67.9 %) TL, ventral precaudal length 73.5 % (73.9 %) TL

Bythaelurus vivaldii, a new deep-water catshark (Carcharhiniformes, Scyliorhinidae) from the northwestern Indian Ocean off Somalia

diagnosis

Diagnosis. A supposedly very small scyliorhinid species with the following characteristics: body firm and stout in presumably adult holotype (slender in supposedly juvenile paratype); snout long (preorbital length 6.1 – 6.6 % TL) and broad, bell-shaped in dorsoventral view with distinct lateral indention; pre-outer nostril length subequal to internarial space; preorbital snout length subequal to interorbital space; preoral snout length 1.4 – 1.8 times in mouth width; eye length 13.9 – 15.0 times in predorsal distance, 6.8 – 6.9 times in head length and 1.6 – 2.3 times eye height; head length 2.6 – 2.8 times width at level of maximum outer extent of anterior nostrils; head width at level of maximum outer extent of anterior nostrils 1.2 times width at level of lateral indention of head, 1.3 – 1.4 times preorbital length, and 8.5 – 8.6 % TL; roof of mouth loosely set with rather small, knob-like to elongated oral papillae, oral papillae on tongue hardly detectable; pelvic-fin anterior margin 2.0 – 2.1 times in pectoral-fin anterior margin; first dorsal-fin base 2.2 – 2.3 times in interdorsal space; length of second dorsal-fin inner margin 1.3 – 2.3 times in second dorsal-fin height; s

Bythaelurus vivaldii, a new deep-water catshark (Carcharhiniformes, Scyliorhinidae) from the northwestern Indian Ocean off Somalia

discussion

Remarks. The holotype has a stout body, whereas the smaller paratype has a rather slender body. Considering that stout body shape is pronounced only in adult specimens but not in juveniles in the morphologically closest congener in the western Indian Ocean, Bythaelurus bachi, it is assumed that the holotype of the new species is supposedly adult, whereas the paratype is presumably immature. Accordingly, a maturity size of females around 30 cm TL is supposed. Its immature reproductive organs evidence the maturity staging of the paratype. The maturity staging of the holotype, however, cannot be verified as its organs were removed. Based on a comparison of the relation between maturity size and maximum size in B. bachi, a maximum size of about 35 cm TL is assumed for the new species. This putative maximum size is based on an exceedance of maximum size vs. maturity size of 18 % in females of its closest congener B. bachi, calculated based on the latter species’ maturity (about 37.7 cm TL) and maximum (about 44.5 cm TL) sizes of females as published by Weigmann et al. (2016). Based on its morphological similarity to B. bachi, it is supposed that B. vivaldii is also an oviparous species.

Bythaelurus vivaldii, a new deep-water catshark (Carcharhiniformes, Scyliorhinidae) from the northwestern Indian Ocean off Somalia

distribution

Distribution. Known only from the upper slope off Somalia, 6 ° 24 ' 1 " N, 49 ° 31 ' 6 " E, in 628 m depth.

Bythaelurus vivaldii, a new deep-water catshark (Carcharhiniformes, Scyliorhinidae) from the northwestern Indian Ocean off Somalia