Unranked clade (stem group ctenophores)
Ctenorhabdotus is regarded as a very primitive ctenophore, possibly representing a stem-group member (Conway Morris and Collins, 1996).
Conway Morris and Collins
Ctenorhabdotus – from the Greek ktenos, “comb,” and rhabdotos, “striped,” in reference to the pronounced striped-like appearance of the comb-rows.
capulus – from the Latin capulus, “a handle,” in reference to the prominent aboral capsule-like element.
Holotype – ROM 50822 in the Royal Ontario Museum, Toronto, Canada.
Burgess Shale and vicinity: none.
Other deposits: none.
Middle Cambrian, Bathyuriscus-Elrathina Zone (approximately 505 million years ago).
The Walcott and Raymond Quarries on Fossil Ridge.
Brief history of research:
Ctenorhabdotus capulus was described by Conway Morris and Collins in 1996 and no additional studies have been published since then.
Ctenorhabdotus is ovoid in shape and bears 24 comb-rows. The top (aboral) and bottom (oral) surfaces are relatively flat. The comb-rows are organised in 8 sets of three, with the central row being much shorter than the two flanking ones. Each group of three comb rows converges towards the aboral side to form 8 strands. The oral region is well developed with an undulating margin. There is a small capsule-like structure on the aboral side of the animal which is thought to include an apical organ and statocysts.
Ctenorhabdotus is rare, known from about two dozen specimens, mostly from the Raymond Quarry. In the Walcott Quarry, this species comprises only 0.01% of the specimens counted (Caron and Jackson, 2008).
The presence of comb-rows suggests the animal was an active swimmer. Its mode of feeding is more conjectural as the mouth is not well preserved and there is no evidence of tentacles.