Function and attachment of the stem in Isocrinidae and Pentacrinitidae: review and interpretation

A review is given of observations and interpretations of the attachment in Isocrinida. It is concluded that all adult Isocrinida discard distal parts of their column and live attached by distal cirri to the bottom or to objects lying on the bottom. From time to time the column may break below a nodal and the isocrinid drift along the bottom until it regains attachment with the cirri. In undisturbed environments a considerable length of the tapering distal part of the column may be maintained, and several specimens may be connected by the entangled distal parts of the columns lying on the bottom. Specimens of Seirocrinus subangularis attached to tree trunks in the Lower Jurassic Posidonia shale of Holzmaden, Germany, have been interpreted as pseudoplanktic. These are all adult specimens with distal parts of their column discarded before they attached themselves to the trunks. Furthermore, since adult specimens cannot swim to the surface, they must have attached themselves to sunken trunks lying on the bottom.