Cytokinesis of Thuricola folliculata (Ciliophora, Peritrichida)

Thuricola folliculata is a sessiline, loricate peritrich ciliate. Its somatic pellicle consists of annular transverse crests and includes the plasma membrane, the alveolus, the electron-dense epiplasm, and the subepiplasmic layer. Cytokinesis occurs along an oral-aboral median plane where two fissures develop, one at the oral and one at the aboral end of the peritrich. Each fissure results from simultaneous formation of two furrows on opposite sides of the cell. At the end of cytokinesis, both trophozoites remain joined to each other by an intercellular bridge. During cytokinesis, microfilament bundles appear at the level of the subepiplasmic layer in the fission plane; they are distributed in two arcs one oral and one aboral, and may be responsible for the formation of the four furrows. The microfilament ring seems structurally analogous to the contractile ring of various dividing cells, where it works like a sphincter. The dence corpuscles, the discontinuous dense borders, and the boundary layer of T. folliculata have not been reported in any other ciliates.