Organisms with a false coelom, like roundworms, are called

Pseudo-coelom.

Explanation:

Coelom may be defined as the body cavity of the organisms. Three main types of coelom are acolomates, pseudocoelomates and true coelomates. Acoelomates does ot conatin any coelom.

Pseudo-coelom are the false cavity present in the organism. Their ody cavity is not derived by the mesoderm but form the blastocoel. They are also known as blastocoelomate. Example includes the roundworms.

Thus, the answer is pseudo-coelom.