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Class Cestoda - covering of ingested eggs is digested away...

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Class Cestoda The class Cestoda consists of the tapeworms, an example of which is shown in Figure 22. The tapeworm scolex (head/neck region) has hooks and suckers that allow the organism to attach to the host's intestinal wall. Behind the head is a short neck and then a long string of proglottids. Each proglottid segment contains a full set of both male and female sex organs and very little other structure. Since the animal does produce wastes, it retains its excretory canals, but no digestive system is needed. Being sessile organisms in a fairly stable environment, tapeworms have only rudiments of nerves. Following fertilization, proglottids become a bag of eggs that when mature, breaks off and passes out with feces. If the eggs of tapeworms are ingested by pigs or cattle, the larvae become encysted in the muscle of the hosts. The
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Unformatted text preview: covering of ingested eggs is digested away and the larvae burrow through the intestinal wall and travel by bloodstream to lodge and encyst in muscle; a cyst is a hard-walled structure sheltering a larval worm. If humans eat the meat of infected pigs or cattle and fail to cook it properly, they too become infected. The Phylum Rotifera Rotifers (shown in Figure 23) belong to the phylum Rotifera, which contains about 2,000 species. Rotifers are often observed in biology lab preparations. Their digestive tract is the inner tube and the rest of the animal is the outer tube (of a tube-within-a-tube body plan). Rotifers are microscopic and abundant in freshwater. A crown of cilia (corona) forms a rotating wheel that serves as both an organ of locomotion and acts to deliver food to the mouth. ....
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