Seasonal atrophy of the visceral organs in a sea cucumber

Abstract

The gut, gonad, respiratory trees, and circulatory system of the commercial sea cucumber Parastichopus californicus are annually lost as a result of atrophy of these organs and not, as originally supposed, through spontaneous, seasonal evisceration. Visceral loss is preceded by cessation of feeding–locomotory behaviour. Torpor ensues, and the visceral tissues are absorbed through a progressive process which includes phagocytosis by the sea cucumber's coelomocytes and, in some instances, the scavenging activities of endosymbionts. Regeneration of the viscera occurs within several weeks. Similar seasonal atrophy of the visceral organs has not been reported to occur in other coelomate organisms. We hypothesize that visceral atrophy in P. californicus is an expression of seasonal diapause induced by reduced food availability.