Burrowing - Mechanics of Locomotion
Some polychaetes are burrowing. Instance is glycerides and capitellidae. Their parapodia are smaller. Burrowing is done by protrusion of proboscis. After that, proboscis is withdrawn into the body and, and the animal crawls in that space. Burrowing in polychaete is different from that in oligochaetes. Oligochaetes depict crawling and digging or burrowing movement. The action of longitudinal and circular muscles on the coelomic fluid creates a peristaltic wave; while the setae, which are fewer in number and are shorter assist in, getting a local grip on the substratum. Neural connections help-in coordinating the peristaltic action by alternate stretching and contraction of muscles. The digging or burrowing action is accomplished by the forward extension of the anterior segments into the spaces of the soil particles. Increase in hydrostatic pressure now causes widening of the space. Now, the animal pulls the posterior part of the body forward.