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Lecture 5 Animal Evolution – The Invertebrates. Earthworms. have hydrostatic skeleton. each segment wall is a layer of circular muscles. worm moves forward by muscle contractions in one segment after another, down the length of its body
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Earthworms • have hydrostatic skeleton. • each segment wall is a layer of circular muscles. • worm moves forward by muscle contractions in one segment after another, down the length of its body • contain nephridia; regulate the volume & composition of body fluids. • Have closed circulatory system
Earthworms • Their brains are known as rudimentary brain • Rudimentary brain: • clusters of cells integrates sensory input & commands for muscle responses for the whole body. • Paired nerve cords; long extensions of nerve cell bodies lead out from the brain.