Superficially, Brachiopods look a lot like bivalve Mollusks (clams, etc.). There are several ways to tell the live creatures apart. The Brachiopod will usually have a pedicle, a long stalk attached to one of the valves, and not much meat inside, just a lophophore. A bivalve Mollusk has no pedicle and lots of good, juicy meat.

None of these do much good when all you have is a shell, and the shell has been a rock for hundreds of millions of years. So you have to look at the symmetry of the shells.

A Brachiopod is equilateral but not equivalved. That is, the two valves (separate parts of a 2-part shell) are not the same, but each valve is symmetrical from one side to the other.

A bivalve Mollusk, like a clam, is equivalved, but not equilateral. The two valves of a clam shell are mirror images of each other, but each valve is asymmetrical to itself.

The exception to all this are the Ostrea, or oysters, which have no symmetry whatsover.

Log in or registerto write something here or to contact authors.