Segmented worms are the most highly developed worms. Their body consists of segments that give the worms a ringed appearance. This group includes polychaete worms, oligochaete worms, and leeches.
Polychaete worms, the largest group of segmented worms, live in the sea and along the shore. Many of these worms have tentacles (feelers) on their head and a pair of leglike projections called parapodia on each body segment. The parapodia are used in crawling. They have many setae (bristles) that help the worms grip the surface on which they are moving. Many polychaete worms live among algae or burrow in mud or sand. Some live in tubes attached to the sea floor. A worm makes its tube from sand or from material secreted by its body. Some polychaete worms eat small plants and animals. Others feed on plant and animal remains.
Oligochaete worms include earthworms and many freshwater species. They have a few setae but no parapodia. Most oligochaete worms eat decaying plant matter.
Leeches make up the smallest group of segmented worms. They grow from 3/8 to 12 inches (1 to 30 centimeters) long and have a flat body with a sucker at each end. Most leeches live in water and feed on the blood of fish and other water creatures.
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