Trichoplax

Trichoplax is a genus in the phylum Placozoa. Its species Trichoplax adhaerens is one of four known Placozoa species, alongside Hoilungia hongkongensis, Polyplacotoma mediterranea and Cladtertia collaboinventa; Placozoa is a basal group of multicellular animals, possibly related to Cnidaria. Trichoplax organisms are very flat, commonly less than 4 millimeters across, and lack any organs or internal structures. They have two cellular layers, a ciliated upper layer of flattened cover cells and a lower layer of cylinder cells bearing locomotory cilia and cilia-free gland cells, with a liquid-filled cavity called the fiber syncytium, held open by star-shaped fibers, between the two layers.