Choanoflagellatea

Choanoflagellatea is a group of free-living unicellular or colonial protists, classified within the eukaryotes. They are characterized by the presence of a single flagellum surrounded by a collar of microvilli. This unique collar structure is responsible for their feeding mechanism, trapping bacteria and other small organic particles from the water as the flagellum beats, creating a current.

These organisms are found in a wide range of aquatic environments, including marine and freshwater habitats, as well as moist terrestrial soils. They can exist as single cells, but many species form colonies, which can be simple clusters or more complex arrangements. The colonial forms are particularly interesting as they are considered to be the closest living relatives to animals, and the study of their behavior and development provides insights into the early evolution of multicellularity.

Choanoflagellates play a significant role in aquatic ecosystems as consumers of bacteria and detritus, contributing to nutrient cycling. Their morphology, particularly the collar and flagellum, is remarkably similar to the choanocytes found in sponges, which are the simplest multicellular animals. This similarity has led to extensive research into choanoflagellates as model organisms for understanding the origins of animal life. Reproduction in choanoflagellates can be asexual, typically through binary fission, and some species also exhibit sexual reproduction.