Abstract
Heterolobosea is a small group of amoebae, amoeboflagellates and flagellates. Since heterolobosean amoebae are highly reminiscent of naked lobose amoebae of Amoebozoa, they were for a long time treated as members of Rhizopoda.
Currently, the Heterolobosea is nested within the eukaryotic supergroup Excavata. The excavate organisms were originally defined on the basis of the structure of flagellar system and ventral feeding groove.
However, Heterolobosea have lost some of these structures. The most important heterolobosean taxon is the genus Naegleria as N. fowleri is a deadly parasite of humans and N. gruberi is a model organism in the research of assembly of the flagellar apparatus.
Both the species have been studied in detail for decades and genome sequence of N. gruberi was recently published. On the other hand, the other heteroloboseans are considerably understudied and undescribed despite their enormous ecological and morphological diversity.
Many heteroloboseans have adapted to various extreme environments; halophilic, acidophilic, thermophilic, and anaerobic representatives have been described. Few heteroloboseans are facultative endobionts of both vertebrates and invertebrates.
Naegleria fowleri and Paravahlkampfia francinae are even able to parasitize humans. The genus Stephanopogon, whose members are multiflagellate, was once considered to be a primitive ciliate and was affiliated with Heterolobosea only on the basis of cell structure and phylogenetic position.
Finally, acrasids have developed a simple form of aggregative multicellularity and represent the only known multicellular excavates. The chapter summarizes information on morphology, ecology, life cycle, phylogeny and taxonomy of Heterolobosea.