A Turbellaria has no skeleton, but has tiny bristles called cilia that help it move at least two layers of muscles under its skin. It has three cell layers called the endoderm, the mesoderm and the ectoderm. They also have the beginnings of a head region. They are a phylum of triploblastic acoelomate invertebrate animals. The word Platyhelminthes comes from the Greek words platy meaning flat and helmins' meaning worm. Their bodies are soft, unsegmented, and flattened with bilateral symmetry and resemble ribbons.