Major distinguishing characteristics: No mouth or alimentary canal
Approximate number of species described: unknown
Natural History
All but two freshwater species are marine. All are aquatic. They live between the grains of sand, in the water column as plankton, or crawling on the substrate or other organisms.
Taxonomy
Some consider this group to be a Subphylum of Xenacoelomorpha.
There are two Classes that traditionally belong to the Phylum regardless of their placement.
Acoela
Nemertodermatida
Anatomy
The Acoelomorpha resemble flat worms. Their internal structures are so simple they have no real internal structures.
The Fossil Record
There is only one known fossil of an acoelomorph, Gutticorpus.
