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Phylum EchinodermataThe phylum Echinodermata is made up of sea cucumbers, sea urchins, sand dollars, sea stars, brittle stars and sea lillies. They are all marine animals and are all found intertidally in our region, except sea lillies which are a deep water group. Echinoderms have a radially symmetrical body which is arranged in five parts. The skeleton is internal, calcareous and covered with skin. It may also have fixed or moveable spines. Another unique feature of Echinoderms is their tube feet, many with suction-cup-like tips, that are operated by an internal water-vascular system. The body is made up of a system of canals through which sea water passes back and forth between the body and the sea. Separating the canals from the sea is a sieve plate that allows the animal the regulate the amount of filtered water that enters the body. Pedicellaridae are a structural specialization unique to sea stars and sea urchins. These pincer-like structures consist of a short stalk protruding, usually in clusters, from the surface of the animal with jaws at the tip. Sea urchin pedicellaridae have three calcareous jaws at the tip, whereas sea star pedicellaridae are only equipped with two jaws. There are many different uses for the pedicellaridae depending on the species. Some species use them to keep settling larvae and debris off of the body, while others use them to capture prey or to defend themselves against predators. |