Placozoans and Xenacoelomorphs

Placozoans and Xenacoelomorphs is a Browse By group of the Nature Atlas that gathers some of the simplest animals known, the placozoans, flat plate-like animals with no organs or nervous system, and the xenacoelomorphs, soft marine worms with a very simple body whose place on the animal family tree is still debated. An entry belongs here when its own cited article describes a placozoan such as Trichoplax or a xenacoelomorph such as Xenoturbella. It excludes the comb jellies and the other minor phyla that have groups of their own. The group lets a reader find the animals whose simplicity makes them important for understanding how the first animals arose.