Bythaelurus

Weigmann, Simon, Ebert, David A., Clerkin, Paul J., Stehmann, Matthias F. W. & Naylor, Gavin J. P., 2016, Bythaelurus bachi n. sp., a new deep-water catshark (Carcharhiniformes, Scyliorhinidae) from the southwestern Indian Ocean, with a review of Bythaelurus species and a key to their identification, Zootaxa 4208 (5), pp. 401-432 : 427

Key to the valid species of Bythaelurus :

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; 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........................... 7. 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................... 6. 6a. Head with distinct lateral indention anterior to outer nostrils; adult claspers rather slender (base width ~1.5% TL) and with knob-like apex.......... B. hispidus [western and eastern Indian Ocean: Kenya to Oman, southern India and Andaman Sea] 6b. Head narrow and without distinct lateral indention anterior to outer nostrils; adult claspers broader (base width ~2% TL) and without knob-like apex........................... B. tenuicephalus [western Indian Ocean: Tanzania and Mozambique] 7a. Labial furrows reduced, with uppers and lowers about equal in length........................................... 8. 7b. Labial furrows distinct, with lowers noticeably longer than uppers.............................................. 9. 8a. 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] 8b. 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] 9a. 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] 9b. Flanks of body lack a line of white spots, ventrally darker, fin tips without broad white areas, caudal fin without dark bands.................................................................................................... 10. 10a. 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] 10b. Coloration lighter; maturity size 36–48 cm TL, maximum size 45–55 cm TL; known only from the southwestern Indian Ocean.................................................................................................. 11. 11a. 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] 11b. 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 n. sp. [southwestern Indian Ocean: Madagascar Ridge]