Figure 1. The form of pseudopodia in three types of amoeboid protozoa. (a) The rhizopod Difflugia (about 250 m long) has broadly lobed pseudopods; these emerge from a shell into which sand grains are incorporated. (b) The heliozoan Actinophrys (cell body 40 m diameter) has axopodia supported by bundles of microtubular fibres. (c) The foraminiferan Elphidium (shell up to 500 m across) has fine reticulopodia forming a network.

Figure 2. The ciliate Tetrahymena has rows of simple cilia and a group of four membranes around the cell mouth (cell about 50 m long).

Figure 3. Examples of flagellate protozoa. (a) The kinetoplastid flagellate Bodo is about 10 m long. (b) The collar flagellate Codosiga (cell 15 m long) is attached by a stalk and has a single flagellum emerging from the centre of the collar. (c) The hypermastigote flagellate Trichonympha (about 200 m long) has numerous flagella and ingests wood fragments at the posterior end.

Figure 4. Spores and infective cells of parasitic protozoan groups. (a) A spore of a member of the Sporozoa (about 20 m long) containing several sporozoites; these emerge as gliding cells (b) with an apical complex, seen here at the upper end. (c) A microsporan spore (about 4 m long) contains a laminated structure and an inverted and coiled polar thread surrounding the infective cell; upon germination of the spore the tubular polar thread everts and penetrates a host cell so that when the infective amoeboid cell passes through the tube (d) it enters the cytoplasm of the host cell. (e) A myxosporan spore (about 20 m long) with a multicellular spore case containing two polar capsules and a single infective cell; the latter emerges as an amoeboid cell (f) in the gut of the host.