Cyclic occurrence of gregarine trophozoites (Apicomplexa) in the burrowing echinoid Echinocardium cordatum (Echinodermata, Spatangoidea)

Abstract

The occurrence of the gregarine Urospora nea-politana in the spatangoid echinoid Echinocardium cordatum was followed monthly over a 1 yr period. Infesting stages (sporozoites) were seen only in the digestive cells of the hosts' gastric caecum while growing stages (trophozoites) only occurred in the hosts' body cavity. Sporozoites showed no variation in abundance over the investigated period. The number of trophozoites, however, clearly varied with a minimum in summer and early autumn. Trophozoite variation appears to be related to the gonadal cycle of the host.