2.6 The opisthokonts

The opisthokont clade is a distinct lineage of eukaryote groups which share an ultrastructural identity and have no evident sister group; it comprises all the true fungi including chytrids, microsporidia, collar-flagellate protists (Choanozoa), and Kingdom Animalia (which includes us in the metazoa)(Fig. 6).

A cladogram (phylogenetic tree) showing the relationships of the eukaryotes
Fig. 6. A cladogram (phylogenetic tree) showing the relationships of the eukaryotes. Note that the top branch of this tree shows the opisthokont clade as distinct from the other eukaryotic clades. The opisthokont clade subsequently diverges into animals and fungi as sister clades. Adapted from the Tree of Life project [http://tolweb.org/Eukaryotes].

All molecular and ultrastructural studies have strongly supported the idea that opisthokonts form a monophyletic group. The name ‘opisthokont’ comes from the Greek and means ‘posterior flagellum’, so the common characteristic that gives them their name is that flagellate cells, when they occur, are propelled by a single posterior flagellum, and this applies as much to chytrid zoospores as to animal sperm. In contrast, other eukaryote groups that have motile cells propel them with one or more anterior flagella (see our Resources Box about the heterokonts).

Resources Box

The heterokonts

Heterokonts are organisms in which the motile cells have unequal flagella. This group includes several fungus-like organisms that have been studied by mycologists.

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Updated December 16, 2016