Ultrastructure of trophozoites of the gregarine Lankesteria ascidiae (Apicomplexa: Eugregarinida) parasitic in the ascidian Ciona intestinalis (Protochordata)

The gregarine Lankesteria ascidiae (Lankester 1872) Mingazzini, 1891 was studied within specimens of the ascidian Ciona intestinalis L. collected from the Bay of Naples. Examinations of parasitized ascidiae by light microscopy showed trophozoites inserted in the host's stomach epithelium or free in the lumen. The gregarine induced an hypertrophic reaction in the host's epithelium cells, and trophozoites free in the stomach were surrounded by cilia of gastric cells. The host cells flanking infected cells appeared laterally compressed and a niche formed as an invagination of the gastric wall covering the trophozoite. Transmission electron microscopy of C. intestinalis gastric epithelium showed mononucleated trophozoites with large mitochondria frequently arranged in peripheral clusters. Maturing trophozoites showed a mucron filled by a dense fibre matrix; these fibres extended in a root-like formation through the whole trophozoite cell up to its periphery and appeared to occupy a separate cytoplasmic compartment enclosed in a membrane. The membrane covering the compact mucron was in continuous close contact with the membrane of the host cell. The trophozoite's cytoplasm was rich in paraglycogen-like inclusions and electron-dense lipid deposits. The surface showed rows of electron-dark knobs protruding at regular intervals from a basal layer. These rows were cross-connected by underlying perpendicular bundles of filaments.