Prokaryotes and eukaryotes are unicellular, made of one cell. Great. Eukaryotes are unicellular or multicellular. But the typical examples of multicellular eukaryotes we have are made of, often, trillions of cells, like us humans. Ants must still be made of many millions of cells. Are there known eukaryotes with very few cells that make them up? Like, 5, or something? Or maybe a dozen cells making up the whole organism in its fully developed state?
There's Trichoplax adhaerens, a Placozoa, made of a few thousand cells. Then there is Dicyema japonicum, a simple mesozoan, made up of 9 to 41 cells. Arguably, the simplest multicellular organism is the algae Tetrabaena socialis, whose body consists of 4 cells. Then, there's the parasitic Myxozoa which have 7 cells.
This nematode always has either 959 or 1031 cells.
Species from Gonium genus are typically 4-16 celled. Gonium pectorale is 16 celled.
Arakaki, Yoko et al. “The simplest integrated multicellular organism unveiled.”, vol. 8,12, e81641. 11 Dec. 2013, doi:10.1371/journal.pone.0081641