First 107 words of the document:
Bivalves are softbodied invertebrates whose shells consist of a pair of calcareous valves.
Bivalves first appeared in the Cambrian but it was not until the Mesozoic that they
developed widely. They have various modes of life and can be marine or fresh water.
You need to be aware of the following features:
Shape and symmetry of valves
Number and size of muscle scars
Pallial line and sinus
On the diagrams below, label the following: Muscle scars
Teeth and sockets