Pellicle

Shape-stabilizing cell boundary complex composed of membranes, microtubules, proteins, and/or polysaccharides (Figs. 1, 2, 3, and 4, Kinete, Fig. 2). Many Protozoa have more than one limiting membrane for at least some of their developmental stages (Table 1). In some groups, the main cell membrane is underlined by one or more inner membranes that are often derived from the endoplasmic reticulum (Fig. 3). This is one of the reasons, why they were grouped into new taxon Alveolata (Classification). Like the outer membranes, these inner membranes are species specific and possess distinct inner and outer surfaces. The characteristics of the inner membranes have been revealed by the methods of freeze fracture (Apicomplexa, Figs. 2 and 3) and negative staining (Fig. 4c). The single outer membrane and the membranous complexes often have subpellicular microtubules (approx. 25 nm in diameter) underneath them (Figs. 2, 3, and 4).

Fig. 1

(a–g) TEMs of parasitic stages which are surrounded by a...