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www.scilinks.org Topic: Asteroidea Keyword: HM60106

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Sea stars are found on rocky coastlines worldwide. One of the more colorful varieties is the African sea star, Protoreaster linckii (a). The sunflower star, Pycnopodiahelianthoides (b), can have up to two dozen arms.

Class Holothuroidea

Sea cucumbers belong to the class Holothuroidea. Most of these armless echinoderms live on the sea bottom, where they crawl or burrow into soft sediment by using their tube feet. The ossicles that make up their endoskeleton are very small and are not connected to each other, so their bodies are soft. Modified tube feet form a fringe of tentacles around the mouth. When these tentacles are extended, as shown in Figure 38-5, the animals resemble the polyp form of some cnidarians. This resemblance explains the name of this class, which means "water polyp." A sea cucumber uses its tentacles to sweep up sediment and water. It then stuffs its tentacles into its mouth and cleans the food off them.

Class Asteroidea

The sea stars, or starfish, belong to the class Asteroidea, which means "starlike." Sea stars live in coastal waters all over the world. They exist in a variety of colors and shapes, two of which are shown in Figure 38-6. Sea stars are economically important because they prey on oysters, clams, and other organisms that humans use as food.

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