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Unformatted text preview: , both of which are shown in Figure 10. Both body forms have tentacles arranged around an opening into the two-layered sac-like body. The inner tissue layer (derived from endoderm) secretes digestive juices into the gastrovascular cavity, which digests food and circulates nutrients (doing the job our circulatory AND digestive systems do). Muscle fibers occur at the base of the epidermal and gastrodermal cells, making this the first group of muscled animals. Nerve cells located below epidermis near the mesoglea interconnect and form a nerve net throughout the body. Cnidarians have both muscle fibers and nerve fibers, making these animals capable of directional movement. The nerve net allows transmission of messages in more than one direction, possibly an advantage in a radially symmetrical animal, while contraction of muscle fibers (under control of the nerve fibers) allows for movement. While they have a nerve net, brains are not present....
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- Fall '10
- Biology, Cnidaria, nerve net, animals. Nerve cells