M is for ... mollusc!

Most (but not all) molluscs have shells - it is these shells you can see on the right. Snails, cockles, mussels, octopus, and squid are all molluscs you will probably have heard of.

Question: These three animals have shells, but one of them is not a mollusc. Which one is it?

a. Mussel
b. Barnacle
c. Cockle