Bythaelurus stewarti

WEIGMANN, KASCHNER & THIEL, 2018



Classification: Elasmobranchii Carcharhiniformes Pentanchidae

Reference of the original description
WEIGMANN, S. & KASCHNER, C.J. & THIEL, R. (2018)
A new microendemic species of the deep-water catshark genus Bythaelurus (Carcharhiniformes, Pentanchidae) from the northwestern Indian Ocean, with investigations of its feeding ecology, generic review and identification key. PLoS ONE, 13 (12): e0207887

Types
Bythaelurus stewarti
Holotype: ZMH: 26251; Paratype: ZMH: 26252; ZMH: 26253; ZMH: 26254;

Images of types

Description :


Citation: Bythaelurus stewarti WEIGMANN, KASCHNER & THIEL, 2018: In: Database of modern sharks, rays and chimaeras, www.shark-references.com, World Wide Web electronic publication, Version 03/2019

Please send your images of "Bythaelurus stewarti" to info@shark-references.com

Bythaelurus stewarti WEIGMANN, KASCHNER & THIEL, 2018, holotype, ZMH 26251, adult male, 425 mm TL © Dr. Simon Weigmann, Elasmobranch Research Laboratory
Short Description
Diagnose after WEIGMANN, KASCHNER & THIEL, 2018 [26877]: A medium-sized Bythaelurus species with the following characteristics: body firm and slender; snout long (preorbital length 4.9–7.4% TL) and broad, bell-shaped in dorsoventral view with distinct lateral indention; pre-outer nostril length 0.6–1.4 times internarial space; preorbital snout length 0.7–1.1 times interorbital space; preoral snout length 0.8–1.7 times in mouth width; eye length 10.2–15.5 times in predorsal distance, 4.9–7.7 times in head length and 1.2–2.3 times eye height; head length 2.2–2.6 times width at level of maximum outer extent of anterior nostrils; head width at level of maximum outer extent of anterior nostrils 1.1–1.3 times width at level of lateral indention of head, 1.2–1.6 times preorbital length, and 8.1–10.1% TL; tongue and roof of mouth densely set with knob-like oral papillae; pelvic-fin anterior margin 1.6–3.5 times in pectoral-fin anterior margin; first dorsal-fin base 1.3–2.3 times in interdorsal space; length of second dorsal-fin inner margin 0.8–2.3 times in second dorsal-fin height; second dorsal-fin base length 5.1–8.9% TL; anal-fin base 0.7–1.9 times interdorsal space. Coloration: dorsally dark grayish-brown with rather indistinct dark blotches at nape, on flank, below both dorsal fins, and across caudal fin; ventral side grayish-white, usually with dark grayish-brown mottling on head. Upper jaw with 64–85 and lower jaw with 64–88 rows of small tricuspidate teeth with outer surface of crown furrowed by strong longitudinal ridges and strongly structured by reticulations; monospondylous trunk vertebrae centra 37–42, diplospondylous precaudal centra 37–45, total centra 125–140. Branchial, trunk and lateral caudal-fin dermal denticles loosely set, their surface very strongly and fully structured by reticulations. Claspers rather long and very slender, gradually narrowing to bluntly pointed tip without knob-like apex, inner margin length 10.1–11.3% TL, base width 1.4–1.5% TL; clasper hooks present along inner edge of large exorhipidion, large envelope overlapping part of clasper groove, inner lobe with rhipidion, cover rhipidion, pseudopera and pseudosiphon. The reproductive mode is yolk-sac viviparous. Bythaelurus stewarti n. sp. differs from all congeners in the distribution, which is apparently restricted to the Error Seamount. It further differs from all congeners in a higher spiral valve turn count (11–12 vs. 6–10) and in the morphology of branchial, trunk and lateral caudal-fin dermal denticles, which are loosely-spaced and not overlapping even in adult specimens of the new species, whereas they are closely-set and overlapping in all other Bythaelurus species. Compared to its morphologically and geographically closest congener, the new species further differs in a larger size, a ventral head with dark mottling, claspers that gradually narrow to the bluntly pointed tip without knob-like apex, and a surface of dermal denticles that is very strongly and fully structured by reticulations.

Distribution
only known from Error Seamount (Mount Error Guyot), northwestern Indian Ocean [26877]

Size / Weight / Age
TL (max): female: 437 mm TL, male: 435 mm; TL (mature): males: at 389 mm, TL (birth): around 150 mm TL [26877]

Habitat
marine; depth range 380–420 m [26877]

Dentition
Upper jaw with 64–85 and lower jaw with 64–88 rows of small tricuspidate teeth with outer surface of crown furrowed by strong longitudinal ridges and strongly structured by reticulations [26877]

Remarks
shark-references Species-ID=15275