opisthokont

Opisthokont is a major eukaryotic supergroup that includes all animals (Metazoa), fungi, and several closely related unicellular lineages. The name derives from the characteristic posterior position of the flagellum in many opisthokont flagellated cells, a feature observed in several early-diverging lineages, though not universal among all descendants.

Taxonomy and phylogeny: The group is defined principally by molecular phylogenetics rather than a single morphological trait. Within Opisthokonta, the holozoan branch comprises animals and their closest unicellular relatives, such as choanoflagellates and filastereans; the fungi and related lineages form the other major branch. The exact relationships among several unicellular opisthokonts remain active areas of research.

Characteristics and diversity: Opisthokonts range from unicellular organisms to highly multicellular forms. In many lineages, adult cells are non-flagellate, but flagellated stages with a posterior flagellum occur in several basal groups, such as choanoflagellates and some fungi. Reproduction varies widely, with sexual and asexual modes observed. The clade is central to studies of the evolution of multicellularity, development, and cellular signaling in animals and fungi.

Evolution and significance: The opisthokont lineage is ancient, with early divergences traced to the Precambrian. Its study informs understanding of the origin of animals and fungi, and of fundamental cellular and developmental mechanisms shared across these lineages.