Trichoplax adhaerens is a simple balloon-like marine animal with a body cavity filled with pressurized fluid. It is given its own phylum, called Placozoa, sometimes referred to commonly as the tablet animals, which is a direct translation from the Greek scientific name; the only other species assigned to this taxon, Treptoplax reptans, was described in 1896 and hasn't been seen since, leading to doubts about its existence. Individual Trichoplax are soft-bodied, about 0.5 mm across, and somewha… (More on Placozoa)