Except for sponges (phyla Calcarea and Silicea), all animals belong in
   Eumetazoa and have tissues.
   Most  Eumetazoa  exhibit  bilateral  symmetry  and  are  classified in
   Bilateria.
   Invertebrates  are  a  paraphyletic  group  that  includes all animals
   except a clade of deuterostomes called chordates.