The word mantle means cloak or cape, and does often resemble a cloak. The edges of the mantle may extend far beyond the main part of the body, forming flaps, double-layered structures adapted for many different uses, including for example, the siphon.
The mantle cavity change
The mantle cavity is a central feature of molluscan biology. This cavity is formed by the mantle skirt, a double fold of mantle which encloses a water space. This space contains the mollusc's gills, anus, and organs for taste, excretion and reproductive organs.
The mantle cavity functions as a respiratory chamber in all molluscs. In bivalves it is usually part of the feeding structure. In some mollusks the mantle cavity is a brood chamber, and in cephalopods and some bivalves such as scallops, it is a locomotory organ.
The mantle is highly muscular. In cephalopods the contraction of the mantle is used to force water through a tubular siphon, and this propels the animal rapidly through the water. In other molluscs, it is used as a kind of "foot" for locomotion.