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Name:
Actinocrinites gibsoni With Lumectaster howelli & Macrocrinus mundulus
Age: Mississippian
Formation: Edwardsville
Location: Crawfordsville, Indiana
Size: Actinocrinites is 3.5 inches long.
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Here is a great specimen that tells a story. This plate is from the famous crinoid site near Crawfordsville, Indiana. On the left of the plate is a beautiful specimen of Actinocrinites gibsoni. The large, stellate-plated crinoid shows the arms, anal tube, and a portion of the stem. Now is when the story begins. A very dark, unusual starfish, Lumectaster howelli, is wrapped around the anal tube of the crinoid. Some people postulate that the starfish was trying to eat the crinoid. However, most authorities are convinced that this association represents a true symbiotic relationship between the two organisms. The starfish lived off the excrement produced by the crinoid. In doing so, the starfish cleaned up the environment so that the crinoid could keep living. Crinoids have to live in a very clean environment or they perish. On the right side of the plate is a specimen of Macrocrinus mundulus. This crinoid displays fine plate structure and great contrast with the matrix. The feathery, biserial arms are complete and exhibit fine pinnulation. The anal tube of this crinoid sticks out beyond the tips of the arms. This is a fabulous fossil specimen of two crinoids associated with a starfish.
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