The Placozoa are a primitive form of invertebrate. They're the simplest in structure of all non-parasitic multicellular animals (Metazoa). They're generally classified as a single species, Trichoplax adhaerens, although there's enough genetic diversity that it's likely that there're multiple, morphologically similar species. A common name doesn't yet exist for the taxon; the scientific name literally means "flat animals". Evolutionary relationships }} }} }} There's no convincing fossil record… (More on Placozoa)