Bythaelurus is a genus of sharks belonging to the familyPentanchidae, the deepwater catsharks. The genus Bythaelurus Compagno 1988 was first described as a subgenus of Halaelurus Gill 1862 based on several morphological characteristics including a soft body with thin skin, a bluntly rounded snout without a pointed, knob-like tip, and eyes not noticeably elevated on the dorsal surface of the head. Members of this genus are generally found in deep water and have more somber body coloration.^[1]

There are currently 14 recognized species in this genus:^[2]

• Bythaelurus alcockii(Garman, 1913) (Arabian catshark)^[1]
• Bythaelurus bachiWeigmannet al., 2016 (Bach's catshark)^[3]
• Bythaelurus canescens(Günther, 1878) (dusky catshark)
• Bythaelurus clevai(Séret, 1987) (broadhead catshark)
• Bythaelurus dawsoni(S. Springer, 1971) (New Zealand catshark)
• Bythaelurus giddingsiJ. E. McCosker, Long & C. C. Baldwin, 2012 (Galápagos catshark)
• Bythaelurus hispidus(Alcock, 1891) (bristly catshark)
• Bythaelurus immaculatus(Y. T. Chu & Q. W. Meng, 1982) (spotless catshark)
• Bythaelurus incanusLast & J. D. Stevens, 2008 (sombre catshark)
• Bythaelurus lutarius(S. Springer & D'Aubrey, 1972) (mud catshark)
• Bythaelurus nayloriEbert & Clerkin, 2015 (dusky snout catshark)^[1]
• Bythaelurus stewartiWeigmann, Kaschner, and Thiel, 2018 (Error Seamount catshark)^[4]
• Bythaelurus tenuicephalusKaschner, Weigmann & Thiel, 2015 (narrowhead catshark) ^[5]
• Bythaelurus vivaldiiWeigmann & Kaschner, 2017 (Vivaldi's catshark)^[6]

A single fossil species, †Bythelurus steurbautiHovestadt & Hovestadt-Euler, 1995 is known from the Early Oligocene of Belgium.^[7]