Chap. 23 COELENTERATES SIMPLE MULTICELLULAR ANIMALS 



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Fig. 23.13. Portuguese man-of-war, Physalia, eating a fish held by the feeding 

 polyps. The float (about 10 inches long) is tilted over on its side with the crest 

 toward the camera. Physalia is a colony of hydrozoan polyps fitted for different 

 functions — feeding, defense, reproduction. They act together in such close coop- 

 eration that they form an individual. Physalia frequents warm ocean currents and 

 is often carried to the shores of Europe and America. (Photograph courtesy, 

 Douglas P. Wilson, Marine Biological Laboratory, Plymouth, England.) 



saucers (strobilas). Some jellyfishes are crystalline clear and colorless; others 

 are rose-tinted, yellow, lavender, blue, or deep red; all their swimming motions 

 have characteristic grace and rhythm. 



Aurelia — A Scyphozoan Jellyfish. Aurelia is one of the commonest of jelly- 

 fishes and most often studied. Drying fragments of them litter the beaches after 

 a storm, great bounty for the sandpipers. The polyps are small and usually 

 hidden in seaweeds (Fig. 23.15). 



A long folded lip trails from each corner of the square mouth (Fig. 23.14). 

 The edges of these are well armed with stinging cells and the fold encloses a 

 groove along which cilia drive minute animals toward the mouth and thence 

 to the four-pouched stomach. There they come in contact with gastric filaments 



