chitons
The shell of certain animals, like turtles, has eight plates because the carapace (upper shell) consists of eight distinct bone plates that have fused together during the animal's development. These plates provide protection and support for the animal's body.
A mollusk is a sea creature that lives within a shell. A cobra does not live in a shell.
THey use a shell
the function of the its shell is to protect the mollusk's very vulnerable and sensitive organs.
Most mollusks have shells outside their soft bodies. The shell is a mollusk's skeleton. It is part of the animal and the mollusk is attached to it by muscles. The soft animal inside can never leave its shell and come back to it. The shell is made of a form of limestone and is built by the mollusk itself. Certain glands in the mollusk are able to take limestone from the water and deposit it in tiny particles at the edge of, and along the inside of, the shell. As a mollusk grows in size, its shell increases in thickness and size. The shell of a mollusk consists of three layers. The outside is covered with a thin layer of hornlike material that contains no lime. Under this is a layer of carbonate of lime. The inside layer is the "mother-of-pearl", or nacre. It is made up of very thin alternate layers of carbonate of lime and a horny substance. The coloring of the shell comes from some glands of the mollusk that contain coloring matter. So a shell may be spotted, all one color, or marked with lines.
Every mollusk except slugs, which have evolved to not need a shell, has a shell. Snails, clams and other bivalves have an external shell. Octopi, squid and cuttlefish have an internal shell.
no
slug
yes
A shell
jellyfish
It is a shell, as in a cockle shell or oyster shell.