. Animal biology. Zoology; Biology. 204 METAZOAN PHYLA small and short spines; they are found on sandy beaches, burying them- selves just under the surface of the sand as the tide goes out but moving about on the sand after the tide has returned. 237. Holothurioidea.—The sea cucumbers, which make up this class, differ from other echinoderms in the fact that they are greatly elongated along the oral-aboral axis, the mouth being at one end and surrounded by branched tentacles, while the anal opening is at the opposite end of the body (Fig. 112). The body wall is muscular and possesses few and sm
. Animal biology. Zoology; Biology. 204 METAZOAN PHYLA small and short spines; they are found on sandy beaches, burying them- selves just under the surface of the sand as the tide goes out but moving about on the sand after the tide has returned. 237. Holothurioidea.—The sea cucumbers, which make up this class, differ from other echinoderms in the fact that they are greatly elongated along the oral-aboral axis, the mouth being at one end and surrounded by branched tentacles, while the anal opening is at the opposite end of the body (Fig. 112). The body wall is muscular and possesses few and small calcareous plates. The madreporite is internal. Tube feet are present and serve as organs for clinging and for locomotion. Ari's-f-o-f-fe. Ampu/fa/ Go/7ac^ Fig. 111.—Internal structure of a sea urchin. {From Dclage and Herouard, "Traite de Zoologie Concrete" after Milne Edwards.) The oral wall of the shell has been removed and the contents of the body are viewed from the oral pole with the Aristotle's lantern and esophagus turned to the left. One type of sea cucumber is represented by those which conceal themselves in the crevices between rocks and which have the tube feet all around the body in five double rows. Some of the tube feet adjacent to the mouth, as well as the tentacles, are used in procuring food. A cloaca is present in a typical sea cucumber and contains the openings of two long branched tubes, the respiratory trees (Fig. 113). Respiration occurs in these as well as through the cloacal wall and the walls of the tentacles and tube feet. The respiratory trees also serve as excretory organs. The madreporite takes water in from the coelomic cavity. Other sea cucumbers possess tube feet on only one side of the body and travel about on that side, looking like huge caterpillars. Still others burrow in the mud like earthworms and have no tube feet at all; they. Please note that these images are extracted from scanned page images that may have been digita
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