autotomy

Autotomy is the voluntary shedding or casting off of a body part by an animal, typically as a self-defense mechanism to escape predation or injury. The term comes from Greek autos “self” and tome “cutting.” Autotomy occurs across a range of animal groups, including reptiles, echinoderms, and crustaceans, and is also found in some molluscs and arachnids.

Mechanisms vary by lineage. In many lizards, tail autotomy occurs at specialized fracture planes in the tail vertebrae and surrounding tissues. A rapid, controlled break allows the tail to detach with minimal blood loss, often aided by contractile muscles and specialized connective tissues. The detached portion continues to move briefly, distracting the predator while the animal escapes. In echinoderms such as starfish and brittle stars, arms can detach at autotomy planes; the residual disk closes off the wound and regeneration proceeds, typically forming a new arm over weeks or months. Crustaceans can shed limbs or claws at designated breakage points, enabling escape.

Regeneration follows autotomy in many species. The lost part is regrown, although the new structure may differ in size, shape, or composition from the original and may require substantial energy and time. Autotomy carries costs, including reduced locomotion, sensory loss, and higher predation risk during regrowth.

Ecologically, autotomy is an adaptive defense that can increase survival after predation attempts. However, it is not universal and is balanced by regenerative costs and ecological context, such as habitat and predator pressure.