Sea star
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 "Asteroidea" from Ernst Haeckel's Kunstformen der Natur, 1904
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Brisingida (100 species[1]) |
Sea stars (or starfish) are animals that live in the ocean. Some live in deep water, and others live on beaches. They have five or more arms and can be more than three meters in diameter.
Despite their common name, starfish actually have nothing in common with fish. For this reason, biologists usually prefer to use the word sea star rather than starfish.
Starfish are invertebrates. They do not have a skeleton or anything that could be compared to bones. They have a nervous system that is special. They do not have a brain. They also do not have blood, instead they use sea water to pump things around their bodies.
There are over 1500 different species of sea star. All of them live in salt water, usually on the floor of the ocean. Most sea stars are predators. They eat mussels, clams, and other bivalves. Occasionally, they might even catch small fish which are unable to get away from their attack.
The crown-of-thorns starfish lives from coral polyps.
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