The Echinoid Directory


Pedicellariae are minute stalked appendages that are found in among the spines of echinoids. They consist of a thin stalk, generally supported by a simple calcite rod, and a tulip-like head which is composed of three (rarely two) valves, each supported by an internal calcitic frame. Pedicellariae attach and articulate to small granules on the surface of the test. In life the pedicellariae are in constant motion. The valves that form the head can open and close and the primary function of the pedicellariae is to keep the surface of the test free of debris and small parasites. There are a variety of different kinds of pedicellariae, the most important being tridactylous, ophicephalous, triphyllous and globiferous. The last mentioned type has poison sacs. See also defence - pedicellariae.