What is the smallest oligocelluar organism?
How many cells does it have?
The question is motivated by this comment@Philosophy.SE
EDIT as recommended in comments
I'm looking for an example of an organism made of very few (the fewer, the better) sister cells (obtained by mitosis or aggregation) that are morphologically and functionally different. I would accept examples of species that exist in different "conformation" (unicellular and multicellular).