Earthworms have no skeleton but during burrowing, the anterior end...

The body cavity (coelom) of earthworm is filled with an alkaline, colourless or milky coelomic fluid containing water, salts, some proteins and four types of coelomic corpuscles, ie, phagocytes, mucocytes, circular nucleated cells and chloragogen cells. The coelomic fluid becomes turgid and acts as a hydraulic skeleton during burrowing. Earthworm (Pheretima posthuma) living in burrows which are made in moist earth. It makes its burrow partly by boring with its pointed anterior end and partly by sucking and swallowing the earth. The body shows metameric segmentation. About the middle of each segment there is a ring of tiny curved bristles called setae or chaetae, formed of a horny nitrogenous organic substance known as chitin. The setae and musculature serve for locomotion as well as for anchoring body firmly in burrow. The blood of earthworm is composed of a fluid plasma and colourless corpuscles, physiologically comparable to the leucocytes of vertebrates.