Ultrastructure of the egg of Sanguinicola inermis Plehn, 1905 (Digenea: Sanguinicolidae)

Eggs of Sanguinicola inermis are the main cause of pathology in the definitive fish host. Eggs were collected from the common carp, Cyprinus carpio, and examined with transmission electron microscopy and optical histochemistry. Eggs, which lack microspines and pores, possess a thin shell with an outer surface of shallow reticulations and inner spherical projections. Internally the egg comprises a homogeneous acellular layer adjacent to a thicker syncytial, metabolically active layer. The latter layer is filled with glycogen and contains many excretory concretions, which are also present within the egg lumen. Portions of the syncytial layer extend towards the egg lumen and are in close proximity to the enclosed miracidium. Histochemical tests on the shell were negative for elastin.