Ultrastructure of vitellarium, vitellogenesis and associated ducts in Maritrema linguilla (Digenea: Microphallidae)

Abstract

Most vitelline cells of Maritrema linguilla within metacercariae are immature and dividing but some have completed vitellogenesis. Increasing numbers of vitelline cells reach maturity in the adult. After completion of vitellogenesis within the vitellarium, the nucleus and later the central cytoplasm of the vitelline cell degenerate. The peripheral cytoplasm degenerates in the vitelline reservoir and the fully mature vitelline cell consists only of plasma membrane surrounding vitelline globules. The ring-shaped vitellarium is surrounded by glycogen-rich parenchyma cells, the cytoplasmic extensions of which intrude between each vitelline cell. The vitelline reservoir and duct are surrounded by a nucleated syncytium bounded externally by muscle fibres. The cytoplasm of the vitelline reservoir syncytium extends deeply into the lumen, embracing mature vitelline cells and absorbing their residual bodies and lipid droplets. The epithelium of the vitelline duct synthesizes a unit membrane to repair or replace the external plasma membrane of vitelline cells.