The ultrastructure of the daughter sporocyst of Cercaria bucephalopsis haimaena Lacaze-Duthiers, 1854 (Digenea: Bucephalidae) from the edible cockle, Cardium edule L.

The body wall of the daughter sporocyst of Cercaria bucephalopsis haimaena Lacaze-Duthiers, 1854, is shown by the electron-microscope to consist of an external syncytial tegument, lying on a basement membrane, and an internal cellular subtegument, which surrounds a body cavity containing developing cercariae. The syncytial tegument has areas of dense cytoplasm alternating with sparse reticulate cytoplasm. The dense cytoplasm contains nuclei, a few mitochondria and secretory products which probably include a neutral mucopolysaccharide. This may be the precursor of the acid mucopolysaccharide in the sparse reticulate cytoplasm and on the surface of the daughter sporocyst. Nutrients are probably absorbed through the outer plasma membrane of the tegument, pass through the sparse reticulate cytoplasm in the middle region of the tegument, the inner plasma membrane and basement membrane into the subtegument. The ultrastructure of the tegument of adult and larval Digenea are compared. We would like to thank Dr Gwendolen Rees for allowing us to examine the electron-micrographs of Parorchis acanthus. We are also grateful to Professor E. W. Knight-Jones for the provision of excellent working facilities and to the Science Research Council, for a grant to one of us (E.A.B.) which made the work possible.