One of the biggest shells I find on our beach is the Florida Fighting Conch (which is around 3 inches long).  The empty shells are often damaged in some way, but every now and then I find a nice one.

If I find one with the snail still inside, I leave it alone.  Or, if it is far from the water, sometimes I help the snail out and throw him back in.

Fighting conch with snout and eyes extended

You often find this sea snail stranded on the beach at low tide, trying to flip itself over with the sharp spike on its foot.



It also uses this spike to defend itself.  And, when the snail is fully retracted into its shell, the spike becomes a little door, neatly shutting intruders out.

The snail has a long snout, with which it gathers food, and eyes which are on stalks.  You can see the snout and eyes in this video:



Here is a snail that has got it right; it is mostly submerged in the sand, staying nice and moist until the tide comes in again.