Limb Shedding Assists Escape

photograph of gray and red starfish on the sand

Biological Strategy

AskNature Team

Image: Florian Berger / Pixabay / Free non-commercial use

Protect From Animals

Animals–organisms that range from microscopic to larger than a bus–embody a wide variety of harms to living systems, including other animals. They threaten through predation, herbivory, defense, and parasitism, and they compete for resources such as water, nutrients, and space. Any given living organism commonly faces threats from a variety of animals, requiring strategies that effectively defend from each. Trout and other bony fish, for example, escape predators by having scales made of very thin, flake-like pieces of bone covered with slippery mucus. They also have behavioral strategies such as camouflage, fast swimming, and twisting and turning to achieve release from a predator’s grip.

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Echinoderms (Sea Stars, Sea Urchins)

Phylum Echinodermata (“spiny skin”): Sea stars, brittle stars, sea cucumbers, sea urchins

Echinoderms get their name from their tough, spiny outer skin, which is clearly visible in some species, like sea urchins. They are known for their five-point radial symmetry and specialized water vascular system, which depends on changes in water pressure to extend or contract tiny tube feet. Pumping water through this system allows echinoderms to eat, move, or cling to surfaces, but it doesn’t generally enable very rapid movement. Some even have the ability to regrow body parts, which comes in handy if a limb is nibbled off by one of the ocean’s very fast-moving predators.

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The limbs of a starfish assist escape because they can be shed.

“Starfishes, which have hard spiny skeletons and five (or more) arms or limbs in a star-like arrangement, are also adept at autotomy when caught by predators. Their subsequent regeneration, however, can be particularly dramatic. As long as the shed limb is not devoured by the predator and still contains a section of the central body disc of the starfish that shed it, this limb has the ability to regenerate into a complete starfish.” (Shuker 2001:132)