Identifying Brachiopods using a Dichotomous Key

A dichotomous key is a technique for identifying specimens by making a series of yes/no choices.

If you examine your fossil carefully, and follow it through the flowchart, you should be able to identify it correctly.
 
 

Brachiopods are particularly well adapted to this kind of identification, since the orders are distinguished to a large extent by characteristics which elementary school students can identify.

You have in your bag, five brachiopods.
 
 

Brachiopods are identified by three criteria which are easy to see.
 

The orientation of the shells.  Most brachiopods are biconvex, but some are concavo-convex, with their shells fitting
together like a pair of stacked spoons.  To help your students learn the terms, I am including a definitional spoon.

The shape of the hinge. Some brachiopods have flat hinges.  (They are called "strophic").  Others have pointed hinges
(They are called "astrophic").
 
 


Strophic

Strophic

Astrophic

The pattern on the surface of the shell.  This is called decoration.  Some have ridges; others don't.

Scientists also differentiate brachiopods by the microscopic structure of the shell and by the form of the feeding mechanism, but amateurs can't make those kind of distinctions.
 
 
 

Older students may be interested in knowing more about the brachiopods they are looking at.
Remember the classification system we use to identify organisms:

               Phylum
                      Class
                          Order
                              Family
                                  Genus
                                      Species

Brachiopods are divided into three classes.  I am only including the orders to which our brachiopods belong.
 

Class Lingulata:  Calcium phosphate shell and hinge of muscle Class Craniata:  Calcium carbonate shell and hinge of muscle Class Articulata:  calcium carbonate shell and hinge of shell.
Order Orthida:  Biconvex shell with strophic hinge
Order Strophemenida:Concavo-convex shell with strophic hinge
Order Rhynchonilida:  Biconvex shell with astrophic hinge.

 

Now, take your fossils and let's identify them.

1.  Is one of the shells concave?

       If yes, the shell is Rafinesquina.
       If no,  go to 2

2. Is the hinge pointed (astrophic)?

       If yes, go to 3
       If no,  go to 4

3.  Is the shell larger than 1 cm?

       If yes, the brachiopod is Orthorhynchula
       If no, the brachiopod is Rhynchotrema

4.  Does the brachiopod have ridges?

       If yes, the brachiopod is Platystrophia
       If no, the brachiopod is Hebertella
 
 

Check your answers