Choanoflagellates
The choanoflagellates are a group of free-living unicellular and colonial flagellate eukaryotes considered to be the closest living relatives of the animals. Choanoflagellates have a distinctive cell morphology characterized by an ovoid or spherical cell body. Movement of the flagellum creates water currents that can propel free-swimming choanoflagellates through the water column and trap bacteria and detritus against the collar microvilli where these foodstuffs are engulfed. This feeding provides a critical link within the global carbon cycle, linking trophic levels.