Hi , sea shells are made by a family of animals known as mollusca which includes slugs, land and water Snails , Bivalves (better known as clams) and even the squid and octopus are included in this family.

In all these animals they share common features that unique to there family..

most of the mollusc family produce a shell of some kind. it is made out of calcium carbonate.. similar to the shells of crabs or even the stoney skeleton of corals.

Calcium carbonat is utilised by seacreatures as a building block as it can be pulled directly from solution in the seawater....

you wanted to know how the shell it made ? ill try and explain ill need to pick an example we'll say a conch shell . a Conch is a Gastropod, meaning stomachfoot in latin.. similar to a giant land snail and the chosen shell for a hermit crab to seek out .

Perfect but tiny snails are produced from sticky eggs deposited on a food source. While devoloping in the egg the embrio snail had allready started making its shell out of calcium carbonate absorbed through the egg wall .. once hatched the snails shell is amazingly thin and fragile . but as they are tiny the hide pretty well .

They eat and grow pertty quicky, so they dont outgrow there shell each evening the snail uses it mantle , which looks like a tongue, to reach out and lay a sticky layer of Calcium carbonate over the outside of the shell..

in snails they do this with a slight twist in the starting point each time, slowly increasing the opening and creating a spiral .

you can age a shell by growth rings similar to aging a tree, look or obvious ridges or bands.

bright colourings and paterns are created specific species genes and also there diet and topography , ie colour if sand around them .

Put some old shells in white vinegar , watch them fizz and disapear into CO2.. proves its Calcium carbonate ..

i hope this helped :)

Richard Lindley ,

Marine Biologist BSc