Are there any living examples of cellular colonies demonstrating very primitive cellular specialization? If so, what do we know about how they assimilate? How independent are the individual cells and what do we know about their behavior (for example, do they, perhaps, migrate to different colonies in certain proximities)?
Probably not what you are looking for but the protozoan slime mold Dictyostelium discoideum lives as free amoebae which can coalesce into a multicellular migratory slug that eventually forms a fruiting body in which some cells form the stalk while others form spores.
Slug formation is by chemotactic signalling with cyclic AMP as the signal. I seem to remember that there is a predatory species of slime mold which uses cAMP to attract D. discoideum as prey, but I can't bring the name to mind and have failed to find it online.