A. Sea stars, like other echinoderms, do have remarkable powers of regeneration, but they're not quite as remarkable as you seem to think! Most sea stars are able to regenerate a lost arm, but studies have dismissed stories of sea stars regenerating from small pieces. A substantial portion of the central disc must remain in order for the animal to regenerate new arms. A single, isolated arm will die.
Of course, every good generality has its exception, and in this case, it is the sea star known as Linckia, sometimes called the comet star. This sea star is able to regenerate an entire individual from a single arm. Often, one can see an animal with one large arm, a tiny body and four associated tiny arms. This newly formed animal resembles a comet (with the central nucleus and tail), thus the common name.
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