How Are Sea Shells Formed?
Whenever you walk alongside a beach, you might have probably seen a seashell lying on the sand which has been washed in by the waves. Hence, the shell will more or less be empty, for it is the home of some dead sea animals.
In fact, shells are generally available in sea rivers and ponds. Whenever people talk of shells, they mean to say about those soft-bodied animals which are known as mollusks.
Most of the mollusks have shells outside their soft bodies. This sort of shell is a skeleton of mollusk. In fact, it is an animal’s part and the mollusk is attached to it by muscles. The shell increases in size and strength as long as the mollusk grows bigger.
Such type of shell is generally made of a form of limestone and, infact, is built by the mollusk itself. Some of the glands in the mollusk enables to take limestone from the water and hence ultimately deposit it in tiny particles alongside the edge of the shell. The shell increases in thickness and size so long as a mollusk grows in size. You might have got the opportunity to see the lines of growth which are marked by ridges that run parallel to the outer edge and you might have observed these growth lines in the shells of oysters and clams. The other kind of ridges are caused due to ridges in the “mantle” of the mollusk or alternatively by muscles in its body.
The mollusk’s shell is generally in three layers. The outer part is covered with a thin layer of hornlike material which contains no lime. In between the outer and inner part, there is a layer of carbonate of lime. The extreme inner part of the layer is the “mother-of-pearl”, or nacre, which is made of very thin different layers of carbonate of lime and a -horny substance.
As far as colouring part of the shell is concerned, it comes from some glands of the mollusk which contain colouring matter. Hence, for all practical purposes it is feasible to have a shell spotted, all one color, one can be marked with lines. There are certain types of a shells which are visible only with the help of magnifying glass. Whereas the giant clam has three to four feet long shells which are easily visible.