The water vascular system has many projections called tube feet, located on the ventral face of the sea star's arms, which function in locomotion and aid with feeding. Skeleton: Sea stars do not have movable skeletons, but instead possess a hydraulic water vascular system. In fact, their evolutionary ancestors are believed to have had bilateral symmetry, and sea stars do exhibit some superficial remnant of this body structure. Starfish typically have five or more "arms" which radiate from an indistinct disk (pentaradial symmetry). They exhibit a superficially radial symmetry. The names sea star and starfish are also used for the closely related brittle stars, which make up the class Ophiuroidea. Sea stars or starfish are marine invertebrates belonging to Kingdom Animalia and phylum Echinodermata, class Asteroidea.
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