Choanoflagellate

Choanoflagellates are free-living single-celled and colonial flagellate eukaryotes, recognised by a single flagellum ringed by a funnel-shaped collar of microvilli that traps bacteria and detritus for food. More than 125 living species are known, found worldwide in marine, brackish and freshwater habitats from the Arctic to the tropics, and many build a basket-like lorica from silica strips. They are the closest living relatives of animals, a relationship supported by genetic work across the 1990s and 2000s, and their cells resemble the collar cells of sponges, so they are used to reconstruct the unicellular ancestor of animals. Some species form simple colonies, and species such as Salpingoeca rosetta are studied by biologists interested in how multicellularity arose.