Starfish are echinoderms, oceanic creatures that possess unique anatomical features. The name starfish is misleading since they are not fish at all, and are more closely related to sand dollars and sea urchins. In fact, the scientific community is in the painstaking process of trying to make the public aware of their name change from starfish to sea star (the task of making a new name common knowledge can often take years). There are around 2,000 species of starfish and they can be found in a variety of ocean habitats.
Spiny-Skinned
Starfish have dermal spines that extend out from their body surface. Echinodermata means “spiny-skinned” in reference to these dermal spines found on most of the marine animals in this phylum. The dermal spines in starfish are obviously visible, but other echinoderms such as sea urchins, have very distinct dermal spines. Starfish have bony skin that is calcified -- a feature that is quite successful in deterring predators. In addition, many starfish use their bright coloring to ward off predators or to camouflage themselves.
Radial Symmetry
Another special feature of a starfish’s, and other echinoderm’s anatomy, is radial symmetry. Animals that have radial symmetry have similar parts that radiate outwards from the center of their bodies. Usually there are five parts extending out in an animal with radial symmetry, and the most commonly seen starfish possess five arms. However, there are some species of starfish that have up to 40 arms.
Water Vascular System
Starfish do not have a brain or any blood. Instead of blood they use filtered sea water in an intricate water vascular system that serves both their moving and feeding needs. For example, at the ends of a starfish’s arms are tube feet. Muscle contractions squeeze water through the tube feet and it creates a suction for suckers located at the end of each tube foot to grasp things and to move.
Regeneration
Another characteristic that is remarkable about starfish is their ability to regenerate limbs and sometimes even whole bodies. Because starfish keep all their vital organs in their arms, in most cases they are able to do this, as long as the main body is intact. Some species of starfish can grow a whole new body from just part of a severed limb.
Feeding
Many starfish have a stomach that comes out of their mouth when they are ready to eat their prey. After they capture a clam or an oyster they open the shell using their tube feet. The cardiac stomach is then released from inside the mouth and consumes their meal while the stomach is still outside of their bodies. Once it is digested, their stomach retracts back into their bodies.
Bree E. Underwood - Bree E. Underwood has been a professional freelance writer since 2005. She has been published on sites like Livestrong, eHow and Bright ...
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