Mesozoa

Mesozoa, a term applied by Van Beneden to a number of extremely simple animal parasites, found in cuttle-fishes, brittle-stars, and some worms. Their cells are in two layers, the inner forming reproductive elements; they have no mouth or gut, and are sometimes very like the larval forms (planulæ) of some jelly-fish and other stinging animals. The name refers to their apparent median position between the single-celled Protozoa and the many-celled Metazoa. See DICYEMIDÆ.