All the internal animal parasites as a group: The entozoa include tapeworms, flukes, nematodes, and roundworms, termed helminths, which thrive inside other animals.

The entozoa are considered to be an artificial group, containing all types of animals living parasitically in others.

A parasitic animal that lives within another animal: Entozoa can be trematodes that infest the internal organs, intestines, muscle, or tissues of other animals.