Acoelomorpha is a phylum of simple, soft-bodied animals that are primarily marine. They are characterized by their lack of a true body cavity, or coelom, which distinguishes them from more complex organisms. Acoelomorphs are typically small, ranging from a few millimeters to a few centimeters in length, and they exhibit bilateral symmetry. These organisms are mostly free-living and can be found in various marine environments, often living in sediment or on algae. Acoelomorpha includes two main groups: Acoela and Nemertodermatida. They play a role in the ecosystem as both predators and prey, contributing to the balance of marine life.