Arm autotomy in asteroids, as tail autotomy in vertebrates, typically occurs when the animal is attacked and appears to facilitate escape. One assumes autotomy has a cost, but it rarely has been demonstrated in the field in vertebrates and never demonstrated in asteroids. The concentration of lipid was 40 % less and the amount of kilojoules 85 % less in the pyloric caeca of the asteroid Stichaster striatus Muller & Troschel (Echinodermata: Asteroidea) with autotomized arms than in those of individuals with intact arms collected in the field. as the pyloric caeca are used as nutrient reserves, individuals with autotomized arms would have a lesser capacity to withstand low availability of food and, as the caecal reserves can be used for gametogenesis, a decreased capacity for reproduction.