The explosive growth of the fossil record of algae and other organisms moves some paleobiologists to dub this the Big Bang period of eukaryotes, beings made of cells with nuclei. Over all Earth, protoctists form communities with bacteria as well as with other protoctists. Manic mixing and matching of populations occurs.
In "colonial" protoctists, a few cells break off from the individual body and regenerate the entire organism. This is not possible for most multicellular protoctists, whose cells, like ours, differentiate (specialize).