![]() ![]() The bumpy-skinned aboral side is covered with loads of tiny pinchers called pedicellariae that help clean the rough surface.Īlthough sea stars cannot see images, eyespots on the end of each arm enable them to see light, dark, and shadows. The top side of the sea star is called the aboral side, because it’s opposite the oral side. The combination of muscular contractions and changes in water pressure causes the tube feet to extend and contract, moving the sea star’s body along the sandy bottom. This hydraulic system channels water to the tube feet through canals. Digestive juices from the stomach dissolve the prey’s body, which is then absorbed by the stomach’s lining.Įxamine the sea star’s central disc and you’ll notice a structure called the madreporite, or sieve plate, which pulls water into the sea star’s water vascular system. The feet pull the mollusk’s two shells apart just enough so that the sea star can extend its stomach from its mouth, located in a structure called the central disc, where all the arms meet. Those sticky tube feet help the animal hold onto its prey - usually bivalves, like clams and scallops. If you look at that side, you’ll see tiny tube feet with suction cups that line each arm. The bottom of the sea star is called the oral surface, because that’s where the mouth is. The sunflower star, for example, may have up to 24 arms! Most sea stars have five arms, although some have seven, and some have 10 or more. ![]() For a clearer idea of radial symmetry, think of a daisy - the white petals are arranged around the yellow center. Echinoderms are spiny-skinned animals that also include brittle stars, sand dollars, sea urchins, and sea cucumbers.Įchinoderms exhibit radial symmetry, meaning that they have a central part, with other parts arranged around that central axis. These creatures belong to the phylum Echinodermata, whose name stems from the Latin words echinos, for spiny (or hedgehog), and derma, for skin. Keep an eye out for starfish, sea stars, or asteroids - all common names for the star-shaped animals that are fun beachcombing finds. If you’re lucky, maybe you’ll find something special. ![]()
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