Source : Webster's Revised Unabridged Dictionary (1913)

Metazoa \Met`a*zo"a\, n. pl. [NL., fr. Gr. ? after + ? an
   animal.] (Zo["o]l.)
   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.

Source : WordNet®

Metazoa
     n : multicellular animals having cells differentiated into
         tissues and organs and usually a digestive cavity and
         nervous system [syn: {subkingdom Metazoa}]