This species is much smaller than Carinaria lamarcki, attaining a maximal size of 40 mm (Bonnevie, 1920). Shell depressed; similar to that of C. lamarcki. Pair of darkly-pigmented, hemispherical structures (termed claspers by Bonnevie, 1920) located posteriorly on either side of the ventral midline of the tail. Other differences between this species and C. lamarcki cited by Pafort-van Iersel (1983) include: 1) visceral mass more darkly pigmented and on a smaller stalk; 2) cutis thinner, with more numerous and smaller tubercles; 3) retinal base of eyes more darkly pigmented; 4) tentacles more strongly developed, right one distinctly smaller than left one. Bonnevie reported that the claspers were present on sexually mature specimens of 30-40 mm length; thus, this structure could not be a juvenile feature that is lost in adults. Reference to these structures as claspers, however, is probably inappropriate. As Tesch (1949) noted they have little to no musculature and probably could not function in mating.
This species was originally described from the North Atlantic as Carinaria lamarcki var. challengeri by Bonnevie (1920). However, Pafort-van Iersel (1983) identified the above mentioned differences between it and C. lamarcki, and showed that its spatial distribution overlapped widely with that of C. lamarcki (i.e., it was sympatric). She concluded that C. challengeri should be recognized as a valid species.