Sea Stars

Starfish or sea stars are echinoderms belonging to the class Asteroidea. The names "starfish" and "sea star" essentially refer to members of the class Asteroidea. However, common usage frequently finds "starfish" "sea star" also applied to ophiuroids which are correctly referred to as "brittle stars" or "basket stars". On almost any seashore, somewhere, there will be starfish - and probably a few of their relatives such as the brittlestars, sea-urchins and sea-cucumbers. About 1,800 living species of starfish occur in all the world's oceans, including the Atlantic, Pacific, Indian, Arctic and Southern Oceans regions. Starfish occur across a broad depth range from the intertidal to abyssal depths (>6000)Starfish are radially symmetric and typically express pentamerism or pentaradial symmetry as adults. However, the evolutionary ancestors of echinoderms are believed to have had bilateral symmetry. Modern starfish, as well as other echinoderms, exhibit bilateral symmetry in their larval forms.

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