Ultrastructure of the rumen ciliate Dasytricha ruminantium

The ciliate Dasytricha ruminantium possesses cilia over the entire surface. Both the oral and somatic kineties are composed of monokinetids comprising a kinetosome, a tangential ribbon of 5 transverse microtubules, a weakly convergent bundle of 5 postciliary microtubules, a short kinetodesmal fibre, and a single microtubule homologous to T(2) of other litostomate ciliates [15]. The reversed orientation of the kineties within and around the vestibulum may be a consequence of the evolutionary migration of the vestibulum from the anterior to the posterior of the cell. The vestibulum leads to the cytostome and a cytopharynx of the rhabdos type [3]. Microtubules lining the exit canals of the posterior contractile vacuole and cytoproct are believed to originate from somatic kinetids. The ecto-endoplasmic boundary layer (eeb) is composed of two microfibrillar layers. A large extension of the eeb connects the vestibulum to the cell cortex but does not form a karyophore as seen in the closely related genus Isotricha [12].