Shells..
Shells are the hard parts of molluscs that give these animals sturdiness.
The shells on the beach are almost always bivalve molluscs, snails or squid.
Often empty shells on the beach have been hundreds of years old, if not thousands of years.
You can even find fossils of over 100,000 or millions of years old.
Only if there are leftover flesh residues or when the two valves are clogged together, you know that the animal has lived in the last few years. Squidfish have a very fragile shell, which are never old.