choanoflagellater

Choanoflagellater (also spelled choanoflagellate) refers to the group Choanoflagellata, a lineage of free-living unicellular or colonial flagellates within the opisthokonts. They are the closest living relatives of animals (Metazoa) and are important for understanding the origin of multicellularity in animals.

Morphology and feeding: Most choanoflagellates possess a single posterior flagellum surrounded by a funnel-shaped collar of microvilli. The flagellum creates water flow that brings bacteria to the collar, where cells capture prey by phagocytosis. Some species are solitary; others form colonies consisting of many cells embedded in a shared extracellular matrix.

Habitat and life cycle: Choanoflagellaters occur in marine and freshwater environments worldwide. Reproduction is primarily asexual by mitotic division, producing two or more daughter cells. Some species form colonies or exhibit sexual reproduction under certain conditions. Colonial species can display coordinated cell behavior that provides insights into the evolution of multicellularity.

Model systems and significance: The best-studied species include Monosiga brevicollis and Salpingoeca rosetta, which are used to explore cell adhesion, signaling, and the genetic basis of multicellularity. Genomic and molecular studies reveal many genes shared with animals, including components involved in cell communication and development.

Evolutionary significance: The similarity between choanoflagellate cells and sponge choanocytes supports the view that animals evolved from a choanoflagellate-like ancestor. Fossil evidence is limited, but molecular analyses indicate that choanoflagellates diverged before the origin of Metazoa, providing a key link in the animal lineage.