Bythaelurus

Weigmann, Simon & Kaschner, Carina Julia, 2017, Bythaelurus vivaldii, a new deep-water catshark (Carcharhiniformes, Scyliorhinidae) from the northwestern Indian Ocean off Somalia, Zootaxa 4263 (1), pp. 97-119 : 114

Key to the valid species of Bythaelurus , modified from Weigmann et al. (2016):

1a. Coloration variegated, with irregularly distributed spots and blotches; markings not symmetrical..................... 2.

1b. Coloration pale, dusky, or with line of pale spots; usually without conspicuous blotches............................ 3.

2a. Grayish with a pattern of dark brown saddle-like markings on back and tail, and with variegated dark brown blotches on flanks; inside of mouth grayish with brown speckles; ventral surface whitish................................................................................................... B. clevai [southwestern Indian Ocean: Madagascar]

2b. Chocolate brown dorsally with pale spots, the largest being about equal in size to eye diameter above midline, smaller below; posterior margin of dorsal, pectoral, and pelvic fins pale; ventral surface pale........................................................................................... B. giddingsi [southeastern Pacific Ocean: Galapagos Islands]

3a. Coloration blackish with hoary gray surface and some fins white-tipped posteriorly; teeth with cusps and lateral cusps of subequal length; validity and generic assignment uncertain............. B. alcockii [northwestern Indian Ocean: Arabian Sea]

3b. Coloration lighter; at least anterolateral teeth in upper jaw with median cusp much longer than lateral cusps............ 4.

4a. Anal-fin base more than 1.5 times second dorsal-fin base length; color light to medium brown above with dusky areas near the fins or indistinct dark blotches, whitish to light brown below (except for B. vivaldii n. sp.); maturity size 22–31 cm TL; maximum size 30–39 cm TL................................................................................ 5.

4b. Anal-fin base equal to or less than 1.5 times second dorsal-fin base length; coloration variable but without dusky areas near fins or indistinct dark blotches; maturity size 32–59 cm TL; maximum size 42–76 cm TL........................... 8.

5a. Tongue and roof of mouth without (or with rudimentary) papillae; coloration largely plain with dusky areas near fins..................................................................... B. lutarius [ western Indian Ocean : Mozambique]

5b. Tongue and roof of mouth with numerous papillae; trunk and tail with 5–6 indistinct, dark blotches (except for B. vivaldii n. sp.)................................................................................................ 6.

6a. Head narrow and without distinct lateral indention anterior to outer nostrils; adult claspers broad (base width ~2% TL) and without knob-like apex.......................... B. tenuicephalus [ western Indian Ocean : Tanzania and Mozambique]

6a. Head with distinct lateral indention anterior to outer nostrils; adult claspers (if known) slender (base width ~1.5% TL) and with knob-like apex....................................................................................... 7.

7a. Caudal fin long, length ~30% TL; mouth rather narrow, width ~7.5% TL; body slender in all maturity stages; low diplospondylous precaudal (~37) and total (~122) vertebral counts............................................................................... B. hispidus [western and eastern Indian Ocean : Kenya to Oman, southern India and Andaman Sea]

7b. Caudal fin short, length ~24% TL; mouth broad, width ~9.2–9.6% TL; body stout in large specimens; high diplospondylous precaudal (~43–44) and total (~135–140) vertebral counts.............. B. vivaldii n. sp. [ western Indian Ocean : Somalia]

8a. Labial furrows reduced, with uppers and lowers about equal in length........................................... 9.

8b. Labial furrows distinct, with lowers noticeably longer than uppers............................................. 10.

9a. Pre-vent length 1.3 times in tail length; preorbital snout length subequal to eye length; length of lateral trunk denticles less than twice their width.................................. B. immaculatus [ western central Pacific Ocean : South China Sea]

9b. Pre-vent length exceeds tail length; preorbital snout length 1.3 times eye length; length of lateral trunk denticles more than twice their width.................................... B. incanus [ southeastern Indian Ocean : northwestern Australia]

10a. Light brown to gray on dorsal and lateral surfaces with a line of white spots on sides of small individuals, whitish ventrally, fin tips with broad white areas, caudal fin also with dark bands............ B. dawsoni [ western Pacific Ocean : New Zealand]

10b. Flanks of body lack a line of white spots, ventrally darker, fin tips without broad white areas, caudal fin without dark bands.................................................................................................... 11.

11a. Color plain dark brown or blackish above and below; maturity size 52–59 cm TL, maximum size 73 cm TL.................................................. B. canescens [ southeastern Pacific Ocean : Peru and Chile, to Straits of Magellan]

11b. Coloration lighter; maturity size 36–48 cm TL, maximum size 45–55 cm TL; known only from the southwestern Indian Ocean.................................................................................................. 12.

12a. Coloration medium to dark brown with light fin edges and a distinct dark dusky-colored snout; dorsal caudal-fin margin with prominent crest of comb-like dermal denticles; tongue and roof of mouth without papillae............................................................................. B. naylori [southwestern Indian Ocean: Southwest Indian Ridge]

12b. Coloration plain beige to light grayish-brown; dorsal caudal-fin margin lacks prominent crest of comb-like dermal denticles; tongue and roof of mouth with numerous, partially composite papillae.................................................................................................... B. bachi [southwestern Indian Ocean: Madagascar Ridge]