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Underside of a sunflower sea star. Sunflower sea stars can reach an arm span of 1 m (3.3 ft). They are the heaviest known sea star, weighing about 5 kg. [4] They are the second-biggest sea star in the world, second only to the little known deep water Midgardia xandaros, whose arm span is 134 cm (53 in) and whose body is 2.6 cm (roughly 1 inch) wide. [7]
Starfish or sea stars are star-shaped echinoderms belonging to the class Asteroidea (/ ˌ æ s t ə ˈ r ɔɪ d i ə /). Common usage frequently finds these names being also applied to ophiuroids, which are correctly referred to as brittle stars or basket stars. Starfish are also known as asteroids due to being in the class
Solaster dawsoni attacking a spiny red sea star, Hippasteria spinosa An adult specimen of Solaster dawsoni afflicted by the Sea star wasting disease off Vancouver. The morning sun star is a predator, feeding mostly on other starfish. It is feared by other stars which move away as fast as they can if touched by a morning sun star.
Animals mainly have bilateral or mirror symmetry, as do the leaves of plants and some flowers such as orchids. [30] Plants often have radial or rotational symmetry, as do many flowers and some groups of animals such as sea anemones. Fivefold symmetry is found in the echinoderms, the group that includes starfish, sea urchins, and sea lilies. [31]
The animal has true image-forming vision. [3] Adult crown-of-thorns starfish normally range in size from 25 to 35 cm (10 to 14 in). [4] They have up to 21 arms. [3] [5] Although the body of the crown of thorns has a stiff appearance, it is able to bend and twist to fit around the contours of the corals on which it feeds.
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Solaster stimpsoni is a large species, growing up to 50 cm in diameter. It can have 8 to 12 arms, but usually has 10. [2] The aboral surface has a distinctive reddish orange colour and is covered with thick paxillae.
Tube feet (technically podia) are small active tubular projections on the oral face of an echinoderm, such as the arms of a starfish, or the undersides of sea urchins, sand dollars and sea cucumbers; they are more discreet though present on brittle stars, and have only a feeding function in feather stars. They are part of the water vascular system.