Gametes: Protozoa

Formation of sexual stages in Protozoa is known for sporozoans including the piroplasms, Ciliata, Opalinata, Hypermastigida (Fig. 7), and recently for trypanosomes (Fig. 6), but definite gametes are not always present (cf. Platyhelminthes/Gametogenesis, Nematodes/Gametogenesis). In the other groups, the formation and fusion of gametes may be hidden. This may occur especially in those cases where the number of gametes is low and where no clear differences between the fusing gametic partners are recognizable. Such isogametes that look similar light microscopically, are found in the Opalinata, some gregarines , piroplasms, and apparently in trypanosomes, where a true fusion of epimastigotes is postulated to occur just before entering the salivary glands. In some gregarines, anisogametes are described where both types of gamonts undergo divisions. In classic Coccidia (e.g., Eimeria spp., Isospora spp.), tissue-cyst-forming coccidians ( Sarcocystis spp., Toxoplasma gondii , etc.), classic Haemosporidia...