Definitions for "Metazoa"
Those animals in which the protoplasmic mass, constituting the egg, is converted into a multitude of cells, which are metamorphosed into the tissues of the body. A central cavity is commonly developed, and the cells around it are at first arranged in two layers, -- the ectoderm and endoderm. The group comprises nearly all animals except the Protozoa.
Multicelluar animals whose cells become differentiated to form tissues.
multicellular animals having cells differentiated into tissues and organs and usually a digestive cavity and nervous system