pseudocoelomate

A pseudocoelomate is any invertebrate animal with a three-layered body and a pseudocoel.

The other platyzoan phyla are mostly microscopic and pseudocoelomate.

Kinorhyncha, a phylum of small (1 mm or less) marine pseudocoelomate invertebrates that are widespread in mud or sand at all depths as part of the meiobenthos.

The Aschelminthes (also known as Aeschelminthes), closely associated with the Platyhelminthes, are an obsolete phylum of pseudocoelomate and other similar animals that are no longer considered closely related and have been promoted to phyla in their own right.