Pentacrinites are an extant form of Crinoids first found in the fossil record during the Ordovician. This specimen shows many disarticulated stems made up of calcitic ossicles. The crinoid has a five- fold symmetry as seen in the pattern on the ossicles of this specimen. The ossicles are all secreted as a single calcite crystal with a porous calcium carbonate structure called a stereom. The calyx and holdfast have both become disarticulated after death and are not seen in this specimen however some smaller ossicles are present that may have the arms. In life the arms (brachia) would not have been easily mobile and were used to filted food, it is thought that Pentacrinites were pseudoplanktonic, attaching themselves to and colonize driftwood. Only at death would they sink to the anoxic sea floor to be preserved. http://www.bgs.ac.uk/discoveringGeology/time/Fossilfocus/crinoid.html http://www.fossilmuseum.net/fossils/Crinoids/Pentacrinus-fossilis/Pentacrinus.htm
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