ABSTRACT
“Being ammonotelic and osmoconform, echinoderms have not differentiated an excretory system.” This wide held and often reported idea is now questioned by a number of morphological and physiological evidences. From ultrastructural investigations and in vitro experiments, Jangoux and co-workers showed that asteroid rectal caeca (Asterias rubens L.) are structurally and functionally analoguous to the proximal tubules of the vertebrate kidney. They were demonstrated to actively excrete chlorophenol red (CPR) that was injected into the asteroid body cavity. The caecal excretory process of Asterias rubens was investigated in vivo using individuals whose size and coelomic fluid volume were grossly similar. Individuals were intracoelomically injected by filtered sea water solutions of CPR alone or of a CPR-para-aminohippuric acid mixture. Preliminary morphological and/or physiological observations were done on three non asteroid echinoderms (viz. the echinoids Sphaerechinus granulans and Echinocardium cordatum, and the holothuroid Holothuria tubulosa).
