Ecdysis of decapod crustaceans is associated with a dramatic release of crustacean cardioactive peptide into the haemolymph

On the basis of detailed analyses of morphological characteristics and beha vioural events associated with ecdysis in a crab (Carcinus maenas) and a cr ayfish (Orconectes limosus), a comprehensive substaging system has been int roduced for the ecdysis stage of the moult cycle of these decapod crustacea ns. In a remarkably similar stereotyped ecdysis sequence in both species, a passive phase of water uptake starting with bulging and rupture of thoraco abdominal exoskeletal junctions is followed by an active phase showing dist inct behavioural changes involved in the shedding of the head appendages, a bdomen and pereiopods. Together with an enzyme immunoassay for crustacean c ardioactive peptide (CCAP), the substaging has been used to demonstrate a l arge, rapid and reproducible peak in haemolymph CCAP levels (increases of a pproximately 30-fold in the crab and more than 100-fold in the crayfish com pared with intermoult titres) during the later stages of active ecdysis, We suggest that the release of CCAP (accumulated in late premoult) from the c rab pericardial organs or the crayfish ventral nerve cord accounts for many of the changes in behaviour and physiology seen during ecdysis and that th is neurohormone is likely to be of critical importance in crustaceans and o ther arthropods.