430 General Biology 



Class HEXACTINELLIDA ( ). Sponges with 



spicules composed of silicon, triaxon in form. 



Class DEMOSPONGIAE ( ). Sponges with 



spicules composed of silicon, not triaxon in form, or skeleton composed 

 of spongin, or with skeleton of both spicules and spongin. 



Phylum COELENTERATA ( ). Diploblastic, 



radially symmetrical animals with tentacles, stinging cells, single gastro- 

 vascular cavity, no anus. Two body forms are prevalent, the hydroid 

 and the medusa. Jellyfishes, polyps and corals. 



Class HYDROZOA ( .^ ). Coelenterates without 



stomodaeum and mesenteries; sexual cells discharged to the exterior; 

 hydroid and medusa forms in the life history of same species, or only the 

 medusa, the latter having a velum. Polyps (including Hydra), a few 

 corals, small jellyfishes. 



Class SCYPHOZOA ( ). Coelenterates with 



only the medusoid, not hydroid form; velum lacking; notches at margin 

 of umbrella. * Larger jellyfishes. 



Class ANTHOZOA ( ). Coelenterates without 



medusoid forms, with well developed stomodaeum and mesenteries. Sea 

 anemones, most corals. 



Phylum CTENOPHORA ( ). Triploblastic 



animals ; symmetry partly radial, partly bilateral ; eight rows of vibratile 

 plates radially arranged. Sea walnuts or comb jellies. 



Phylum PLATYHELMINTHES ( ). Triplo- 



blastic, bilaterally symmetrical animals with body flattened, with a single 

 gastrovascular cavity (sometimes wanting) and no anus. Flatworms. 



Class TURBELLARIA ( ). Free-living flat- 



worms with ciliated epidermis. Planaria. 



Class TREMATODA ( ). Parasitic flatworms 



without cilia but with a hardened ectoderm, usually parasitic and with 

 attaching suckers. Flukes. 



Class CESTODA ( ). Parasitic flatworms with 



the body differentiated into a head (scolex) and a chain of similar joints 

 (proglottides), the whole being usually regarded as a colony. Tape- 

 worms. 



Phylum NEMATHELMINTHES ( ). Bilat- 



erally symmetrical, triploblastic animals with an elongated cylindrical 

 body covered with a cuticle, with a true body cavity, and a digestive 

 tract with both mouth and anus. Roundworms. 



Phylum ECHINODERMATA ( ). Radially 



symmetrical (with minor exceptions), triploblastic animals with well 

 developed coelom, and usually with five antimeres, spiny skeleton of 

 calcareous plates, and organs of locomotion known as "tube feet" 



