Membrane specializations in the ciliate Euplotes crassus at the site of interaction of the ampules with the plasma membrane.

In Euplotes crassus, the ampules which occur in groups that surround the cilia at their base are organelles which, unlike the extrusomes such as mucocysts and trichocysts, persist inside the cytoplasm and are not lost after discharge. By freeze-fracturing cells, we found membrane specializations denoted by the presence of particles arranged in organized patterns, at the attachment sites of the ampules to the plasma membrane. At each attachment site, an annulus and a rosette were observed in the ampule and in the plasma membrane, respectively. On this basis, it was suggested that the ampules of Euplotes might be cortical organelles functioning in secretion and, therefore, phylogenetically related to the other protozoan extrusomes.