CLASSIFICATION OF ANIMALS 21 



CHIEF PHYLA OF THE ANIMAL KINGDOM 



Subkingdom PROTOZOA 



1. Protozoa (protos, first; zoon, animal). Animals made 

 up of a single cell. The cells may grow together in colonies 

 but never show any division of labor as tissues. Examples: 

 Amoeba, Euglena, Paramoecium, malarial parasite, Volvox. 

 8500 species. 



Subkingdom METAZOA 



2. Porifera (porus, pore; fero, carry). The body radial 

 or without definite symmetry, filled with numerous small 

 inhalent pores, and with one or more large apertures where 

 water is expelled. Cellular tissues and germ, or repro- 

 ductive, cells are well developed, but not laid down in 

 fundamental germ layers. A skeleton made up of lime, 

 silica, or horny material is often present throughout the 

 body. Peculiar cells bearing collars line some of the canals 

 cf the interior. Tissues are well developed but there are 

 no organs. This phylum includes the sponges, which are 

 attached and usually grow up from the bottom somewhat 

 like water plants. 2500 species. 



3. Coelenterata (koilos, hollow; enteron, intestine). The 

 body radially symmetrical, usually with four or six anti- 

 meres; diploblastic (with two primary cell-layers); with a 

 single gastrd-vascular cavity and no anus. The body-wall 

 is provided with peculiar stinging structures the nemato- 

 cysts. Examples: Hydra, jellyfishes, zoophytes, polyps, 

 and corals. 4400 species. 



4. Ctenophora (ktenos, a comb; phoreo, I bear). Animals 

 possessing radial combined with bilateral symmetry; with 

 eight radially arranged rows of paddle plates; triploblastic 

 (with three primary cell layers) ; anus usually present. Sea 

 Walnuts or Comb-jellies. 100 species. 



5. Platyhelmia (platys, flat; helminthos, a worm). Flat, 

 bilaterally symmetrical, triploblastic animals; with a single 

 gastro- vascular cavity having no anus, or without a diges- 



