The choanoflagellates are a group of free-living unicellular and colonial flagellate eukaryotes considered to be the closest living relatives of the animals. As the name suggests, choanoflagellates (collared flagellates) have a distinctive cell morphology characterized by an ovoid or spherical cell body 3-10 µm in diameter with a single apical flagellum surrounded by a collar of 30-40 microvilli (see figure). Movement of the flagellum creates water currents that can propel free-swimming ch… (More on Choanoflagellate)