Original: Brooks\/Cole-Thomson Learning, Belmont, USA The cilia allow the worms to glide along in the water between sand grains, although they also have muscles that allow the body to twist or contract.
Simplified: 7th ed, Brooks\/Cole-Thomson, Belmont, USA The cilia allow the worms to glide along in the water between sand grains, although they also have muscles that allow the body to twist or contract.