Monday, February 26, 2007


phylum Platyhelminthes
Flat worms are aquatic and free-living organisms. Some flatworms may be carnivores that feed on tiny aquatic animals and others maybe scavengers that feed on dead animals. Free-living flatworms have a gastro vascular cavity with one opening at the end of a muscular tube called a pharynx. Once pharynx sucks food into the gastro vascular cavity, intestine is formed with many branches along the body of the flatworm. In the intestines, enzymes break down food into small particles and these particles are taken inside the cells of the intestinal wall. Because intestine branches are spread along the body of the flatworm, tiny food particles diffuse to other body tissues. Unnecessary materials that cannot be digested exit through the mouth like cnidarians.

Parasitic flatworms feed on blood, tissue fluids, or pieces of cells inside the body of their host. Some of parasitic flatworms have pharynx to suck food into intestinal sacs where food is digested.

★ Tapeworms, which lives within the intestines of their host, do not have digestive tracts. They have suckers with absorb the food that has already been broken down by the host’s digestive enzymes.

phylum Nematoda
Roundworms have a long tube-shaped digestive tract with opening at the both ends. Food enters through the mouth and leaves through an opening called anus.
Free-living roundworms are carnivores that eat tiny animals. Some digest bacteria and fungi that break down dead organisms.
Some parasitic roundworms attach to the roots of green plants and absorb juices which damage many croups around the world and others live in plant tissues to collect nutrients.

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