Placozoa are a type of simple aquatic animal. However, they are not particularly well-known, so it is helpful to know some synonyms that can be used instead. One alternative term is Trichoplax, which is the genus name for this group of organisms. Other synonyms include the common names of "flat amoeba" and "plate animal." Placozoans are unique in that they lack a nervous, digestive, or circulatory system. They are also quite small, usually measuring only a few millimeters in length. Despite their simplistic form, they are still of interest to scientists studying animal evolution and genetics.