Bacteria are the important part of the multicellular story. ~ American cytologist Nicole King
Choanoflagellates are free-living unicellular and colonial flagellate eukaryotes. These plankton are the closest living relatives of animals.
In a colony, choanoflagellates are more than an aggregation. Instead, they are an interacting cluster, demonstrating the basic mechanics for multicellularity.
Colonial choanoflagellates only exhibit this behavior under the influence of resident bacteria. Bereft of bacteria, they do not inch toward acting in a multicellular manner.