How to Tell a Brachiopod From a Bivalve

Brachiopods and bivalves are common invertebrate fossils. They are often confused for one another because they both have a pair of shells connected by a hinge. However, you can follow these simple steps to help differentiate between these two types of fossils.

Instructions

1

Compare the two shells of the fossil. If the valves are mirror images of each other, your fossil is a bivalve. If one valve is smaller than the other, you are looking at a brachiopod.

2

Look at each shell of your fossil separately. If you can draw a line of symmetry down the middle of each shell, then your fossil is a brachiopod. If you can't do this, then your fossil is a bivalve.

3

Observe the hole often found on brachiopods. Many brachiopod shells have a hole or groove in the middle of the shell hinge where the brachiopod was attached to the ocean bottom.

4

Take note of the special features of bivalves. Look at the pair of shells together. Many bivalves have gaps along the edge of the shell which allowed the animal to both breathe and move when it was alive. On the inside of bivalve shells, you are likely to find one or more rough circles where muscles were attached.

5

Compare the ways in which you usually find brachiopod and bivalve fossils. Brachiopod fossils are usually found with their shells together, whereas bivalve fossils are usually found with their shells separated. This is because brachiopods had many muscles that kept their shells from separating.