636 



APPENDIX B 



produces, by budding, the sexual, often free-swimming medusa or jellyfish gen- 

 eration. The presence of tentacles furnished with highly specialized stinging cells 

 known as nematocysts is another unique characteristic. 



The coelenterates are divided into three classes. With the exception of the 

 Portuguese man-of-war and a few other showy forms, the first class, Hydrozoa, 

 comprising the freshwater Hydra (Figs. 13.5 and 32.9), the marine colonial 

 hydroids (Obelia, etc.), small jelly fishes, and the hydrocorals, is known chiefly 

 to students of aquatic life. The group consists of thousands of species, some very 

 common and many very beautiful. 



Fig-. B.5. Corals (Anthozoa, order Madreporaria). Left, model of part of colony of Sider- 

 astraea, showing expanded polyps, a polyp in cross section (upper center) and empty polyp 

 cups or thecae. Right, the skeleton of the common rose coral, Manicina areolata, showing 

 elongate thecae formerly occupied by fused, many-mouthed polyps. (Courtesy American 

 Museum of Natural History and University of Miami Department of Biology, respectively.) 



To the second class, Scyphozoa, belong practically all the large jellyfishes 

 (Fig. 32.2), familiar seashore sights, their often vivid coloring and brilliant phos- 

 phorescence making them conspicuous. 



Sea fans, sea feathers, most of the corals (Fig. 33.19), and all the sea anemones 

 make up the last class, Anthozoa, some members of which are familiar to all 

 visitors to the seashore. 



Approximately 4,500 species of this phylum are known. 



Phylum IV. CTENOPHORA (te nof or a; Greek, ktenos, "comb," 

 phoros, "bearing"). 



The sea walnuts or comb jellies. Relatively simple marine Metazoa, 

 exhibiting the following characters: 



