How do starfish regrow lost arms?

Sea stars are echinoderms, related to sea urchins and sand dollars, and are not fish at all; there are around 1,900 known species. Many can deliberately shed an arm to escape a predator, a defence called autotomy. Cells at the wound site then rebuild the missing arm, including its nerves, tube feet and the eyespot at its tip. Because important organs extend into the arms, regrowth takes a lot of energy and can take months or even a year or more. A few species, such as those in the genus Linckia, can even regrow an entire new body from a single detached arm.