Author Affiliation, Ana.
Geography and Geology; Faculty of Pure and Applied Sciences
Contractile tissues in the cirri of ancient crinoids: Criteria for recognition.
Date of Publication
Stalked isocrinid and 'stalkless' comatulid crinoids are able to relocate by crawling on or swimming with their muscular arms. Reattachment is achieved using cirri containing contractile tissues that produce aboral flexure. The following cirral adaptations for active attachment were observed during a SEM study of two comasterid comatulids, Davidaster rubiginosa (Pourtales) and D.discoidea (Carpenter): synarthrial articulations; fulcral ridges corresponding to short axes of ossicles; cirri flattened laterally; each cirrus with a claw at the tip and an aboral attachment pad; cirri serrated aborally and distally. Epizoans are only able to encrust single ossicles in actively motile cirri. These adaptations are associated with crinoids with muscular arms that are used in relocation. Such a suite of characters is unknown in Palaeozoic crinoids; the ability to relocate evolved in crinoids only during the Mesozoic.....