Produced by the Population Genetics and Evolution class, Furman University

The Ordovician: Crinoids
Crinoids are echinoderms, like sea stars and sea urchins. About 500 crinoid species exist today, and most are free-swimming. However, there are still some, called "sea lilies", that express the primitive sedentary morphology. Most extinct crinoids (and a few extant ones) have a stem that anchors the organism to a substrate and supported its pentaramous body (Borths 2008). The body, or "calyx", contains the digestive and reproductive organs of the organism. The tube feet on the arms of this echinoderm are oriented perpendicularly to the incoming water current in order to capture food particles (Borths 2008). Extant crinoids are the only remaining examples of attached, suspension-feeding echinoderms. Now, their habitat is usually located in deep water so viewing them in the wild is quite difficult (Simison 1996).When crinoids first radiated during the Ordovician, however, they comprise a major component of shallow reef communities. Indeed, some reef deposits are completely composed of the carbonate endoskeletons of crinoids (Ausich and Messing 1998).

Page by Ignas Gaska
Fossil crinoid assemblage. Picture provided by: Why files.

Ausich WI, Messing CG. 1998. Crinoidea. Tree of Life project. Accessed Feb. 2010.

Borths M.2008.Crinoids in Lilliput: Morphological change in class Crinoidea across the Ordovician-Silurian Boundary. Ohio State University Thesis: pg 7.


Simison WB.1996. Introduction to the Crinoidea. University of California Museum of Paleontology. Accessed Feb. 2010.