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Thursday, Sept. 25, 2003


Flatbottom Sea Star

* Japanese name: Kihitode
* Scientific name: Asterias amurensis
* Description: Sea stars are echinoderms, in the same family as sea urchins and sea cucumbers, though unlike those animals they are not eaten in Japan. Like all echinoderms (which means "spiny skin" in Greek), sea stars have a five-way radial symmetry. This means they have five "arms," with suckers on the bottom. These are often called starfish, but they aren't fish. For one thing, they lack an internal skeleton. And on their surface, at the center, is the anus; their mouths are located just opposite -- on the underside. Each arm has an "eye," really just a light-sensitive spot that can sense the general direction of light. There are sex organs at the junction between arms. Flatbottom sea stars can grow up to 25 cm in diameter.
* Where to find them: Only in the sea, never on land or in fresh water, and always on the sea floor. Large rock pools are a good place to look for them.
* Food: The suckers of the sea star's arms help it hold onto the sea floor when the current is strong, and also help it catch prey, including barnacles, snails, sea urchins, clams and mussels. The sea star forces open the shell of its prey and eats the contents, even through the smallest of gaps.
* Special features: Some of the bumps on the surface of the sea star are used to absorb oxygen, and some are organs the sea star uses to clean itself. This prevents barnacles from growing on its surface. If an arm of a sea star is damaged, it can be "dropped," in a way similar to how lizards can discard their tails. The sea star then regenerates a new arm. In some species, the arm can be dropped even when it is not damaged. In this case, a new arm is grown back, and the old arm can regenerate a new body.

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