The rôle of the body fluid in relation to movement in soft-bodied invertebrates I. The burrowing of Arenicola

Abstract

This investigation is an attempt to obtain quantitative results on the method of functioning of the body-wall muscle-coelomic fluid system of the lugworm which was chosen as an example of a worm having this system in a relatively simple condition. Measurements of the hydrostatic pressure developed in the coelomic fluid during various phases of activity, particularly during burrowing, were recorded, and the mechanism by which pressure is differentially distributed throughout the body is discussed. The relation of pressure changes to burrowing movements is described and some calculations of the thrust which can be exerted by the worms are given. It is shown that the forces available to the worms are insufficient to allow of straight­-forward burrowing and that the ability to burrow depends on the thixotropic properties of the muddy sand in which the animals live.