Thyonidiinae

Heding & Panning, 1954

12 Genera, 6 monotypic; 40 species

Simple calcareous ring without forked tails. The individual members of the calcareous ring are undivided. These undivided members correspond to Cucumariinae and Colochirinae of the Cucumariidae. The only difference between the Cucumariinae and the Colochirinae is that the exoskeleton evolved differently. There is a consensus that the construction of the calcareous rings has the same roots as the construction of the exoskeleton. For these reasons, we set in the beginning of this subfamily two groups with many genera, which have plates for the calcareous bodies of the epidermis, as also with the Cucumariinae and the Colochirinae. (Panning & Heding, 1954)

Tentacles 15-25. Calcareous deposits in body wall, plates or tables. (Pawson, 1970)