Figure 4. Transmission electron microscopy of the attachment apparatus of Ancora sagittata.

(A) Longitudinal section of the gregarine forebody embedded in a host cell shows a large frontal vacuole (fv) and amylopectin granules (ap) within the attachment organelle and the main part of the cell; the black arrows indicate the base of the contact zone (circular groove, see B); (B) Longitudinal section through the base of the contact zone between the gregarine and host cell under a higher magnification: gregarine cell forms a circular groove (black arrow) pinching the host cell; the rear wall of the frontal vacuole (double arrow) arises from this area; parallel filaments (fi) arise from the groove zone backward; the white arrow indicates the terminus of the internal membrane complex (imc) of the pellicle; pm is the plasma membrane of the gregarine cell.