The Animal Kingdom - 631 



Fig. 32-7. A sea anemone. Phylum Coelenterata; Class Anthozoa. This glass model shows one expanded speci- 

 men (on the right), with many elongate tentacles surrounding the mouth; and one contracted specimen (on the 

 left). Both individuals are of the same species (Megalactis fWffifhsi) and both are attached to a rock. (Courtesy 

 of the American Museum of Natural History, New York.) 



scattered rather diffusely throughout the 

 body of the coelenterate. In other words, the 

 cells are not aggregated into clearly recog- 

 nizable tissues, such as are found in higher 

 animals. 



(5) The symmetry of the coelenterate body 

 is radial, rather than bilateral (as in higher 

 animals generally). 



(6) All Coelenterata possess nematoblasts 

 (Fig. 32-8). These highly specialized cells 

 enable the animal to capture a variety of 

 small active food organisms. Each nemato- 

 blast contains a tiny bladder, called the nema- 

 tocyst, from which a coiled thread, the nema, 

 can be discharged forcibly and instantane- 

 ously. There are several kinds of nema, how- 

 ever. Some are sharply pointed syringes that 

 can inject a paralyzing substance (hypno- 

 toxin) into the prey. But others are merely 

 coils, which may be single or multiple. Some 

 such coils are laden with a sticky secretion, 



while others are armed with microscopic 

 barbs, and these structures are very effective 

 for snaring and holding prey while it is 

 being paralyzed by the stinging nemae. 



(7) Digestion in the coelenterate is partly 

 extracellular — by means of enzymes secreted 

 by gland cells into the saccular enteron — and 

 partly intracellular — in the individual food 

 vacuoles of the flagellated cells of the en- 

 teron. A larger mass of food material soon 

 disintegrates as it begins to be digested in the 

 enteron. Then the smaller bits of organic 

 food are picked up by the flagellated cells. 

 Thus Coelenterata (and Porifera) seem to 

 have retained, to a greater or lesser extent, 

 the digestive mechanisms of their unicellular 

 forebears. 



(8) All Coelenterata possess a number of 

 tentacles, grouped around the mouth, and 

 these are armored with an especially heavy 

 concentration of nematoblasts. No head is 



