One of the best designs for exoskeletons is the bivalve.  This consists of two shells connected on one side.  This is a useful design because it can open and close, and it can grow to keep up with the growth of the animal inside.

Three phyla found in Nashville use the bivalve design.
 

• Bivalve mollusks:  similar to modern clams and oysters.

• Brachiopods:  looking somewhat similar to bivalve mollusks, but no longer commonly found on beaches

• Arthropods:  Ostrocods-small shrimp-like animals living in tiny bivalve shells

Can you tell a bivalve mollusk from a brachiopod?

Consider the following shells.  Some of them are modern shells.  Som of them are fossils.  Write down the letters of the ones you think are modern.
 

A	B	C
D	E	F
G	H	I
J	K

When you are finished you can check your answers.

All of the three modern shells are mollusks.  Study them carefully and compare them with the fossils.

Two of the fossils are mollusks.  The other six are brachiopods.

Identify the two fossil mollusks.  Explain why you chose them.

When you are finished, you can check your answers.