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[[File: Earthworm movement all.jpg|thumb|A simplified image showing Earthworm movement via peristalsis]]
The [[earthworm]] is a limbless [[annelid]] worm with a [[hydrostatic skeleton]] that moves by peristalsis. Its hydrostatic skeleton consists of a fluid-filled body cavity surrounded by an extensible body wall. The worm moves by radially constricting the anterior portion of its body, increasing length via hydrostatic pressure. This constricted region propagates posteriorly along the worm's body. As a result, each segment is extended forward, then relaxes and re-contacts the substrate, with hair-like [[setae]] preventing backward slipping.<ref name=Quillin>{{cite journal |author=Quillin KJ |title=Ontogenetic scaling of hydrostatic skeletons: geometric, static stress and dynamic stress scaling of the earthworm lumbricus terrestris |journal=The Journal of Experimental Biology |volume=201 |issue=12 |pages=1871–83 |date=May 1998 |doi=10.1242/jeb.201.12.1871 |pmid=9600869 |url=https://jeb.biologists.org/content/201/12/1871.long|doi-access=free }}</ref> Various other invertebrates, such as [[caterpillar]]s and [[millipede]]s, also move by peristalsis.
==Machinery==
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