Thyone

Jäger, 1833

41 species

Body usually thick, ovoid, more or less attenuating, especially posteriorly. Body wall thin, soft. None of the lateral tentacles enlarged. Tube feet spread over entire body, with serial arrangement indistinct except in young specimens where they are restricted to the radii, forming double rows. Radialia in the calcareous ring usually with a double posterior prolongation. Calcareous deposits of various forms, but not large spinous scales, sometimes absent; often prominent spicules around the anal opening, i.e. anal teeth. (Mortensen, 1927)

Ten tentacles. The calcareous ring is put together with long forked tails. In the skin are 2 columned tables. Differs from Havelockia in that in the introvert there are rosettes and no tables. (Panning, 1949)

Tentacles 10. Tube feet scattered on body wall, never restricted to ambulacral radii. Calcareous ring with long posterior projections, each made up of several pieces of calcite. Body wall ossicles tables with a spire of two pillars. Introvert may contain rosettes only, tables only, or tables and rosettes. (Pawson & Miller, 1981)

Thyoninae with 8 large and 2 small tentacles; tube feet scattered over all the body. (McKenzie, 1991)