part of body wall muscle invertebrate muscular system body wall muscle A worm's body wall has two kinds of muscles that it uses to crawl. Circular muscles surround the worm's body and can make the body shrink or spread out. Longitudinal muscles run the length of the body and can shorten or lengthen the worm. Setae (bristles) prevent the worm from slipping. BTO:0001863 BrendaTissueOBO wall muscle