POL'YZO'A (Neo-Lat. nom. pl., from Gk. Troi.oc, polys, much, many + cc,Zop, zoon, animal), or Moss ANIMALS. Minute marine animals usu ally forming moss-like or coral-like calcareous or ehitinous masses called 'corms,' each cell con taining a worm-like creature with the digestive tract flexed, the anus situated near the mouth. The body is usually drawn in and out of the cell by the action of retractor and adductor muscles. The month is surrounded by a crown of long tentacles. No heart or vascular system exists. and the nervous consists of a single or double ganglion situated between the mouth and vent, with nerves proceeding from it. The Poly zoa are hermaphroditic. mnitiplying by budding or eggs. The embryo passes through a morula, gastrula. and troehosphere stage, the corm being formed by the budding of numerous cells from a primitive one. The group was formerly called 'Bryozoa.' Fossil Polyzoa are common in nearly all geo logical formations from the Ordovician upward. Because of the difficulties attendant upon their identification, very few of them have served as hori 2011 -ma rkers or index fossils. The one prom
inent exception to this rule is the genus Archi medes, with its screw-shaped axis, \shnvr is so abundant in some parts of the Carboniferous rocks. In North America the Trenton, Chwin nati, and Hamilton groups are especially prolit'e sources of supply. The European Mesozoie and Tertiary deposits abound in them, one author, D'Orbigny, having described about 850 species from the Upper C'retaevous heds alone, while the rocks of these ages in North America are com paratively lacking in them. The North American Paleozoic has afforded about 1325 species, distrib uted under 170 genera. See Von Zittel and East man, Textbook of Paleontology, vol. i. I New York and London, 19011) : and Nickles and Bass ler, "Synopsis of American Fossil Bryozoa, In cluding Ifibliog.raphy and Synonymy." Bulletin of the rnited States Geological Surrey, No. 173 (Washington, 1900).