Question

What do you mean by visceral mass and mantle.

Answer 1

Visceral Hump

The visceral hump, or visceral mass, of gastropods is always contained within the shell; it generally holds the bulk of the digestive, reproductive, excretory, and respiratory systems. A significant part of the visceral hump consists of the mantle, or pallial, cavity. In both prosobranchs and shelled opisthobranchs this is a cavity completely open anteriorly; in pulmonates it is closed except for a narrow pore. The mantle tissue at the forward edge of the cavity secretes the shell. The upper surface of the mantle cavity serves a respiratory function. In marine species the ciliated lining of the mantle cavity helps produce a water current that passes posteriorly across the gill, or ctenidium, and the osphradium, which is thought to be a sensory receptor that can detect chemical changes in the environment. Both organs lie on the left anterior side of the cavity. The water current sweeps across the posterior part of the mantle cavity, where the nephridiopore, or kidney opening, lies; the water current then passes anteriorly along the right margin past the anus, through which undigested particles of food are eliminated, and usually moves past the gonopore, through which sexual products are released. Cilia on the gill play an important role in water flow through the mantle cavity; they also help some species (e.g., Crepidula) capture food particles.
The mantle cavity serves as a space for the head and foot when these organs are retracted. Many land pulmonates apparently also use the mantle cavity to retain water. Prosobranchs use the operculum, the horny or calcareous disk located on the back of the foot at the posterior end, to seal the shell opening after the head and body have been retracted.


The Mantle

The mantle is an
importantportant part of the body of a mollusk. It forms the outer wall of the mollusk's body. The mantle encloses the mollusk's visceral mass, which is its internal organs, including the heart, stomach, intestines, and gonads. The mantle is muscular, and many species have modified it to use for siphoning water for feeding and propulsion.
In mollusks that have shells, such as clams, mussels, and snails, the mantle is what secretes calcium carbonate and a matrix to form the mollusk's shell

In mollusks that lack shells, such as the slug, the mantle is completely visible. In some mollusks with shells, you can see the mantle extending from under the shell. This leads to its name, which means cloak or robe. The Latin word for mantle is pallium, and you may see that used in some texts. In some mollusks, such as the giant clam, the mantle can be very colorful. It can be used for communication.

The Mantle Margin and Siphons

In many types of mollusks, the edges of the mantle extend beyond the shell and are called the mantle margin. They can form flaps. In some species, they have been adapted to use as a siphon. In species of squid, octopus, and clams the mantle has been modified as a siphon, and it is used to direct water flow for several purposes.
Gastropods draw water into the siphon and over the gill for respiration and to search for food with chemoreceptors inside it. The paired siphons of some bivalves draw water in and expel it, using this action for respiration, filter feeding, excreting wastes, and reproduction.
Cephalopods such as the octopus and squid have a siphon called the hyponome that they use to expel a jet of water to propel themselves. In some bivalves, it forms a foot that they use for digging.

The Mantle Cavity

A double fold of the mantle creates the mantle skirt and the mantle cavity inside it. Here you find the gills, anus, olfactory organ, and genital pore.