Topics: Flatworm, Digestion, Cestoda Pages: 3 (656 words) Published: April 21, 2002
Flatworms are parasitic unsegmented, bilaterally symmetrical worms that lack a coelom but that do have three germ layers. Some forms are free living but many are parasitic. Flatworms have a cephalized nervous system that consists of head ganglion(brain), usually attached to longitudinal nerve cords that are interconnected across the body by transverse branches. Flatworms lack a respiratory or circulatory system, these functions take place by absorption through the body wall. Nonparasitic forms have a simple, incomplete gut, even this is lacking in many parasitic species. Most types of flatworms are called Parasitic tapeworms and flukes.

Examples of Animals in Phylum:

Tapeworms, Class Cestoda, are creatures that live as mature organisms that live on a host. These hosts include cats, dogs, cows, whales, and humans. Human hosts usually occur when uncooked, infected meat is eaten, or by ingesting the eggs. Human infection with a common dog tapeworm is transmitted by infected fleas, and is most commonly seen in children. Immature larval tapeworms may be found in various tissues throughout the body, where they may cause numerous symptoms. Clinical symptoms are usually diarrhea, nausea, and weakness. Also, the health of the person may be compromised. Tapeworms may also disable a person's ability to absorb vitamin B12.

Flukes, Class Trematoda, are mostly internal parasites of animals, particularly vertebrates. In fluke life cycles, eggs are shed into the intestine or bladder for quick exit into water. An egg hatches into a larva, which swims about until it finds a snail (clam in a few cases) of the correct species and then burrows into it. The larva then begins multiplying using the snail's resources. The final stage is a sac of free-swimming larvae, called cercaria, which then burrow out of the snail and go swimming after their next host. Almost every species of vertebrate animal has flukes that...
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