Unlike annelid worms, the body of mollusks does not have a segmental structure, but in most, you can distinguish the head, body and leg. The body of mollusks of most species is completely or partially covered with a shell, while annelids do not have a shell. The shell plays the role of the external skeleton in molluscs. And in annelids, the supporting function is performed by an internal cavity filled with liquid. The movement of molluscs is provided by individual muscles, and in annelids, by the skin-muscle sac. The circulatory system in mollusks (with the exception of cephalopods) is open, while in most annelids it is closed. Molluscs, unlike annelids, have special organs such as the kidneys and the digestive and salivary glands. The nervous system of molluscs is represented by separate nerve nodes connected by nerves, while annelids have an abdominal nerve chain with branches of nerves in each segment.
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