Mantle

The Mantle is a soft, fleshy outer covering, formed from the body of brachiopods and mollusks, sometimes strengthened by calcified plates made of barnacles. The mantle secretes the shell in species that possess shells like brachiopods and mollusks. The mantle in brachiopods has a dorsal and ventral lobe. It is covered with small nipple-like projections. These nipple-like projections are called papillae and they penetrate the shell. The mantles in the mollusks have the left and right lobe. It is joined at the edge to form siphons, which directs the flow and drainage of water out of the mantle. The mantle is the dorsal body part. The flaps are the protruding mantle out of the mollusk's body.

Mantle in Molluscs

The mantle in molluscs is the dorsal body wall that hides the visceral body part. The flaps are protruding mantle out of its body. The epidermis of the mantle secretes calcium carbonate and conchiolin in many species of mollusks. This secretion helps in the formation of shells. Many sea animals like sea slugs lose their shells. It frequently loses its shell and its mantle acts as the dorsal surface. Cloak or cape are the two original meanings of the mantle. In the case of mollusks, a mantle means a cloak. Many species have extended mantle margins. The edges of the margins are flap-like, double-layered structures. It has many uses and purposes like a siphon.

Mantle Cavity in Molluscs

The mantle cavity in mollusks is their central biological feature. The mantle skirt, which is double folded, forms the cavity. The mantle skirt encloses the water cavity. A mollusk’s gills anus, osphradium, nephridiopores, and gonopores are present here. The mantle cavity in mollusks acts as the respiratory chamber. It is a part of the feeding structure in bivalves. In cephalopods and scallops, the mantle acts as the locomotory organ but in some mantles, the mantle cavity is a brood cavity. To force water through a tubular siphon in cephalopods, contraction of the mantle takes place. In the case of gastropods, the mantle cavity is used as an afoot. In bivalves, the mantle cavity helps in filtering food out of water. Pressure increases with the increase of the depth since it has to support the whole body weight. The pressure is 137 GPA at the bottom of the mantle. 

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Functions of Mantle

Functions of mantles are as follows:

• The primary function of a mantle is to enclose and protect the internal organs. The mantle cavity is located inside the mantle, in the mollusk body. It holds water and acts as a respiratory organ. 

• Mantle also acts as a mode of communication. The bright colors of the mantles attract species.

• The mantle cavity in mollusks also consists of gills. Gills are present in the mantles of freshwater mollusks.

• The mantle cavity helps mollusks to filter food particles.

• The mantle cavity in mollusks also protects the egg till they are fully matured.

• The mantles of gastropods help in locomotion. The feet of Bivalvia are too soft and hence cannot locomote. They use the mantle cavity for digging purposes.

• In some mollusks, the mantle acts as a brood chamber. 

What are the Differences Between Mantle and Shell?

More about Mantle Information

The jet propulsion method is used by the squids and cephalopods to swim. It expels the water from the mantle cavity with force after drawing it inside. Jet propulsion is the cause of vigorous such movements. Gentle jet propulsions are for breathing purposes. It circulates oxygen through water in the gills and the mantle. Fast swimming squids have 35% of the mass of their body concentrated in the mantle cavity. Circular muscle fibers contract inside the body walls to squeeze water out of the mantle cavity. Cephalopods have no longitudinal muscle fibers. The collagen fibers on their muscle walls prevent it from lengthening when it contracts. The mantle cavity expands by elastic recoil of the tissues after the relaxation of circular muscles. The shell walls are secreted by the mantle lobes. The ligament and the hinge teeth are secreted by the mantle crest. Thickness increases uniformly, but growth occurs at the margins.