Many leeches found in lakes are parasites, feeding on the body fluids of fish and other creatures. Leeches can swim by undulating their body. However, mostly, they move by using the suckers at either end of their body to loop across the surface of objects. They eat the body fluids of of fish, frogs, water snails and insect larvae. They feed by attaching themselves to their prey and use either jaws or a proboscis to feed on blood. Fish wait for their victims by waiting outstretched. They are very difficult to see because they look just like plant stems. Leeches often consume more than their own body weight in a single meal and often rest, between meals, for up to a month.
Flatworms are unsegmented worms with flattened bodies. Their flatness allows them to shelter beneath stones. The surface of their bodies are covered with cilia which are kept in constant motion, allowing them to glide over plants and stones. They secrete slime which acts as a lubricant. They eat small animals including crustaceans, and insects, alive/dead. Their mouth is a small hole found halfway down the underside of their body. They can sense when food is around, because of sensory cells on their head. They extend a muscular tube out of their mouth, and suck up food. This tube is known as a pharynx. They are eaten by leeches and great diving beetles.
Earthworm bodies are divided into lots of different segments. Earthworms play an important role in helping to keep soil in good condition. They help to recycle plant material, and also mix oxygen into the soil as they tunnel. There are about 13 different types of earthworm in Britain.Earthworms move by contracting the circular muscles around their bodies, then the long muscles which run down their bodies. They eat mainly dead plant material. Earthworms sometimes drag leaves into their burrows and they eat the soil and use the dead plant material from it as food.
http://www.naturegrid.org.uk/biodiversity/invert_english.html
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