Cercaria vaullegeardiPelseneer, 1906 (Digenea: Hemiuridae); development and ultrastructure

Abstract

SUMMARYCercaria vaullegeardidevelops in daughter sporocysts within the digestive gland of the prosobranchGibbula umbilicalis. On emergence into the host mantle cavity the cercarial body retracts into the cystophorous tail, the ‘encysted’ cercaria being then shed into the sea. The encysted cercaria is described at the ultrastructural level for the first time and developmental stages are redescribed. The cercarial body has no penetration or cystogenous glands: a single type of sub-tegumental secretory cell produces vesicles containing neutral mucopolysaccharides which pass into the tegument at encystment. The immotile cystophorous tail consists essentially of a fibrous caudal cyst and 8 appendages including a delivery tube. Scanning electron micrographs show the surface of tegumental membranes enveloping the caudal cyst to be covered with a honeycomb pattern of indentations derived from electron-lucent vesicles produced by the caudal gland. The fibrous-walled delivery tube comprises proximal and distal sections and a modified terminal end-piece.