Crinoids: Sea lilies
Crinoids are echinoderms, a group that includes the starfish, sea urchins, and sand dollars. Sometimes called sea lilies, crinoids resemble long-stemmed flowers, but they are marine animals. A holdfast at the base of the animal’s stem functions like a root that holds the animal in place. The animal’s cuplike body, or calyx, is composed of a mosaic of geometric plates. The calyx has many arms that open into a fan-like net so the crinoid can feed on microscopic food particles. The flexible stem is composed of a series of button-like discs called columnals. When crinoids die, their stems fall apart, or disarticulate, into columnals. The lumen, a hole in the middle of the stem, contained a tube for carrying nutrients to the stem and holdfast. The mouth of the crinoid is on the top of the calyx.
Crinoids first appeared in the Cambrian and diversified until the Permian extinction, when their numbers were greatly reduced. Complete crinoid fossils may occasionally be found in Wisconsin’s Silurian and Devonian rock, but most crinoid fossils consist of scattered columnals. In the Paleozoic, crinoids lived in colonies in shallow waters, but today they live in deeper regions of the world’s oceans.