. Principles of modern biology. Biology. 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, s
. Principles of modern biology. Biology. 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 mechani
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