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Acastoides Trilobite small
Crinoids or sea lilies belong to the phylum of echinoderms (Echinodermata). Just like other echinoderms they have a pentaradial symmetry. Despite their name sea lilies are certainly animals. Nowadays sea lilies are rare in shallow waters, but they used to be as abundant as their relatives sea stars and sea urchins, also echinoderms. Crinoids were attached to the sea floor, but there have been free-swimming species as well. Other species had a float bulb or lobolith which enabled them to float in the water upside down and move through the water.
On top of the stalk is the calyx with a mouth and arms to filter food from the water. Most extant crinoid species are free-swimming and don't attach to the sea floor or anything else. Crinoids can be found in sediments from the Ordovician up to now. In Palaeozoic sediments they can be found in large numbers.
In certain sediments you can find numerous crinoid stalks.
Often only the stalks of crinoids are found. The 'heads' or calyx are much rarer to find. After the animal has died the stalks break up in many small segments. Sometimes complete layers of rock are composed of disarticulated crinoid stalk segments (Crinoidal limestone).
Photos and locations for Crinoidea on this site
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