Cyclocrinus, an enigmatic Jurassic-Cretaceous crinoid

Abstract

Previously undescribed material in the Natural History Museum Basel provides the basis for a reappraisal of the enigmatic Middle Jurassic to Early Cretaceous genus Cyclocrinus D'ORBINGY known only from mostly single columnals and attachment discs. Only one of the previously described Jurassic species, C. rugosus, is recognized despite wide variation in morphology of columnals ranging from Bajocian to Oxfordian in age. A small percentage of columnals are axillary, show facets for side branches or are arched, which has led to the assumption that Cyclocrinus columnals represent radicular cirrals and should be assigned to the Order Bourgueticrinida. Both hypotheses are rejected. The prevalence of single columnals is explained by the restriction of loose, galleried (α) stereom to an area near the facets and around the axial canal; through-going ligament fibres responsible for the preservation of pluricolumnals were thus largely absent from much of the stereom. Cyclocrinus variolarius (SEELEY) from the Albian of England hardly differs from the Jurassic C. rugosus. The ordinal position of Cyclocrinus and of the family Cyclocrinidae SIEVERTS-DORECK is left open though the form has some resemblance to the Early Jurassic millericrinid genus Amaltheocrinus KLIKUSHIN. © Birkhaueser 2008.