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What is a Crinoid?

page 10



Crinoids are often called "sea lilies" or "feather stars". and are echinoderms (spiny-skinned animals) with skeletal parts made of calcareous (limy) plates. They have radial symmetry, digestive, nervous, reproductive and water vascular systems. Their delicate arms strain tiny marine life from the sea and move it toward its mouth.
Some crinoids are stationary, while others move freely over the ocean floor or in floating mats. They may be found in all of the oceans of the world and at vastly different temperatures and depth.

The Crown includes the arms and the body, or calyx, of the animal. The Calyx is the plate-covered body. It contains the digestive systems and supports the arms, which help gather food. The plates of the calyx are arranged in a specific manner for each type of crinoid. Arms are the long appendages that reach out from the calyx. Pinnules are small extensions of the arms that help move water and food to the mouth.  The Stem is made of individual disks with a central opening for nutrients and nerve impulses. Free living crinoids often lack stems.  

Columnal, or stem sections, is held together by flexible fibers which allow movement.

 Shape and surfaces of the columnals may vary with each type of crinoid. Cirri are the "arms of the stem" that hold the crinoid to objects or the sea floor. The Hold Fast secures the crinoid to the sea floor much like tree roots. Free moving crinoids do not have hold fasts.


This slab holds the remains of crinoids and other invertebrate that died on the Iowa sea floor 350 million years ago. At that time Iowa was located near the equator and submerged under a warm sea.

The death of these animals was non-violent and their bodies drifted into this depression to gently settle onto the limy mud. Layers of lime covered their remains and preserved them from destruction. When excavated their bodies lie randomly across the stone and show no current or wave action.


We do not know why these animals died. Did the water temperature rise? Did the salinity become change? Were they suffocated by water that was too muddy ? We may never know.


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