Lower Jurassic Crinoid

© Craven & Pendle Geological Society

Pentacrinites

Published courtesy of Mike Simms, Department of Geology, Ulster Museum, Botanic Gardens, Belfast


Pentacrinites fossilis: a crinoid from the Lower Jurassic of the Dorset coast.

Crinoids, the most primitive surviving member of the echinoderms, use their often finely branched arms as a filtration fan for plankton. Most fossil crinoids bore a stem by which to raise the filtration fan above the sea floor. 

Pentacrinites was a very unusual crinoid in that it lived suspended from floating driftwood. A close relative was the largest known crinoid Seirocrinus subangularis, with stems sometimes more than 20 metres long and a filtration fan more than a metre across.