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The carnivorous snails have tongues that are covered with thousands of tiny teeth to tear apart food. The gastropod fossils from Jacksboro, TX shown below are from the Pennsylvanian, Finis formation, and these gastropods lived about 300 million years ago.
Remove these ads. 1  Common types of shells include sea shells, snail shells, turtle shells and eggshells. 2  There are more than 50,000 varieties of mollusk shells. 3  Some open like clam shells, while others are shaped in a spiral and have a single hold where the animals enters and exits the shell.