Mollusc shell

The mollusc (or mollusk) shell is typically a calcareous <a href="/facts/Exoskeleton/Wlmru4GW">exoskeleton</a> which encloses, supports and protects the soft parts of an animal in the <a href="/facts/Phylum/ELT3Jyax">phylum</a> <a href="/facts/Mollusca/1elgknsQ">Mollusca</a>, which includes <a href="/facts/Snail/y94YHrPw">snails</a>, <a href="/facts/Clam/5BB6vVl7">clams</a>, <a href="/facts/Tusk_shell/9YzqgvC6">tusk shells</a>, and several other classes. Not all shelled molluscs live in the sea; many live on the land and in freshwater.
The ancestral mollusc is thought to have had a shell, but this has subsequently been lost or reduced on some families, such as the squid, octopus, and some smaller groups such as the <a href="/facts/Caudofoveata/VvmrQjvN">caudofoveata</a> and <a href="/facts/Neomeniomorpha/kaPeEyEY">solenogastres</a>. Today, over 100,000 living species bear a shell; there is some dispute as to whether these shell-bearing molluscs form a monophyletic group (conchifera) or whether shell-less molluscs are interleaved into their family tree.
<a href="/facts/Malacology/ajD3luB7">Malacology</a>, the scientific study of molluscs as living organisms, has a branch devoted to the study of shells, and this is called <a href="/facts/Conchology/QrDIVx60">conchology</a>—although these terms used to be, and to a minor extent still are, used interchangeably, even by scientists (this is more common in Europe).
Within some <a href="/facts/Species/oDg6b96r">species</a> of molluscs, there is often a wide degree of variation in the exact shape, pattern, ornamentation, and color of the shell.

Mollusc shell open-in-new

Mollusc shell