The skeletal system forms the framework for body structure of an animal. They support the whole body system. Invertebrates have internal or external hard but non-bony substances as their skeleton. Type of skeleton is the characteristic feature of the phylum which an animal belongs to. Snail belongs to the largest phylum Mollusca which comprised of invertebrate animals. They show diversity in their behavior, habitat in addition to their structural organization.
The Structure of Skeleton system of Snail
Snails and slugs are collectively known as gastropods. Not every gastropod is possessed with a shell but most of them do have it. Snails have a hard shell on their back which serves as the skeleton. The shell on the back of snails is the external skeleton or also called exoskeleton. They provide the wide surface area for the attachment of muscles. These also take up the role of camouflage and protection from mechanical stress and predators. Especially in land snails, shells protect them from sun and water loss. Actually, every gastropod has a shell but in slugs during embryonic development, it has reduced and eased their mobility.
Gastropod shell consisted of three differentiated layers majorly made up of calcium (calcium carbonate) and about 2 percent of protein. Unlike animal body structures, these shells are non-cellular structures. Mantle tissue is a part of molluscan’s body which are present in the shell. Mantle tissues are in direct contact with the shell. They secrete and precipitate out minerals like calcium and proteins for the shell formation. Thus, proteins act as the building block while calcium polishes the shell.
The exoskeleton never sheds hence the shell grows from bottom to top as the body enlarges. The three layers of shell include an inner pearly layer of nacre, the prismatic layer, and proteinaceous periosteum. Among these, the inner and middle layers are calcium rich and calcified while the outer layer is uncalcified and made up of proteins. Shells vary in shape and size as well. Typically, spirally coiled shells are observed but in some varieties like limpets, shells are cone-shaped.
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