Ultrastructure, biogenesis, and functions of extrusive organelles in selected non-ciliate protists

The ultrastructural features, biogenesis and functions of several selected protist extrusive organelles are discussed. Most of the review focuses on some common extrusive organelles that were not considered by Hausmann and several types which have been described since that review of 16 years ago. For convenience, extrusomes are categorized as projectile or mucocyst extrusomes. The projectile extrusomes are further subdivided into non-penetrating and cell penetrating extrusomes. This review is restricted to projectile extrusomes such as ejectisomes, the microsporidian invasion apparatus, and the gun cell of oomycetes. Mucocysts include the apicomplexan rhoptries, the K2 bodies of oomycetes, and the spermatial vesicles and adhesive vesicles of red algae. The possible phylogenetic importance of some extrusive organelles is briefly considered.