The uterine epithelium of Gyrodactylus kobayashii (Monogenea: Gyrodactylidae): ultrastructure of basal matrices, cytoplasmic membranes and the birth plug, and comparison with other reproductive epithelia.

Ultrastructural details of reproductive epithelia in the viviparous monogenean Gyrodactylus kobayashii are described. Specimens of G. kobayashii were fixed for transmission electron microscopy in glutaraldehyde in sodium cacodylate buffer followed by either 1% aqueous osmium tetroxide or 1% aqueous osmium tetroxide reduced with 1.5% potassium ferricyanide. All reproductive epithelia are underlain by a fibrillar basal matrix. The uterine basal matrix is electron-opaque after potassium ferricyanide reduced osmium tetroxide fixation suggesting the presence of carbohydrate-containing materials. With potassium ferricyanide reduced osmium tetroxide fixation, two prominent membrane systems were distinguished in the uterine epithelium. Basal invaginations are short infoldings of the basal membrane. The basal invaginations are common in other reproductive epithelia and tegument and probably enhance transport of materials by these epithelia. Laminated membranes are membrane stacks, resembling endoplasmic reticulum stacks. These membranes were abundant at the apical membrane. The birth plug is a solid cytoplasmic layer, lacking a lumen, and rich in cytoplasmic vesicles. This layer connects the tegument and the uterine epithelium.