BRACHIOPODS Phylum: Brachiopoda Classes: Articulata Inarticulata   Orders: 7 Articulate 4 Inarticulate

MORPHOLOGY:  Copy diagram on page 125 a) and b) Black to show a typical articulate brachiopod. They have 2 VALVES (shells) that totally enclose the soft parts. The average size is 20 - 70 mm but can range up to 370 mm. The valves can open and are hinged at one end; muscles open and close the shell.

Morphology 2 They usually allow water into the shell, as they are filter feeders extracting food from seawater. The two valves are different in size (as opposed to bivalves). However; they do show a line of lateral symmetry along the middle of the animal. Highlight this on your diagram.

Morphology 3:Naming of the valves The smaller valve is the BRACHIAL valve (upper in life position). The larger valve is the PEDICLE valve (lower in life position). The animal secretes the valves as it grows, the original small shell is called the UMBO and the shell grows outwards from either side of this point. Make sure that you can see the umbo on a hand specimen.

Morphology 4: Often the pedicle valve has a small circular opening (FORAMEN) at the end through which a type of foot extends called the PEDICLE. Make sure that you can see the foramen in a hand specimen. The pedicle allows the brachiopod to attach itself to the sea floor. Inside the shell the body fills much of the body cavity.

Morphology 5: Some shells like rhynchonellids have a wrinkly COMMISURE with FOLDS (one on either side of the sulcus) and a SULCUS (in the middle). Draw a rhynchonellid showing the fold and sulcus and the inhalent and exhalent currents. Folds have inhalent and sulcus has the exhalent.  The currents are therefore separated. The crenulated commissure also provides a greater surface area.

The important muscles are: INTERNAL FEATURES: The inside of the shell is the MANTLE CAVITY and is mainly the LOPHOPHORE, which is a food gathering and water-filtering device.  Draw diagram (d) from page 125 Black. The important muscles are: At the posterior end is the pedicle “foot” type of ligament/muscle which when extended could usually reach outside of the shell. The main muscles were the ADDUCTOR and DIDUCTOR muscles, which were used to close the shell.

Internal morphology 2:  Draw diagrams from page 125 Black: c) for muscle position. e) and f) showing internal views of shells with muscle scars. Both sets of muscles were attached to the shell and although not preserved in the fossils there are scars left from where the muscles were attached to the shell. The CARDINAL PROCESS and HINGE acts as a fulcrum on which the muscles can pull. The diductor muscles contract and pull down the cardinal process and open the shell.

Internal Morphology 3: As the diductor muscles relax the adductor muscles contract and close the shell. Role of the lophophore is to act as a feeding device, which collects suspended particles. Some brachiopods like spiriferids have a spiral calcite support called a lophophore support or spiralia. Draw diagram d on page 137.

Internal morphology 4: On the diagram you can see that the brachiopod has TEETH (pedicle valve) and SOCKETS (brachial valve). What do you think the role of these are?

Articulate Brachiopod Orders: There are 7 orders. (including Productids). For each draw a simple diagram. Make a note of the type of hinge line: Long or Short

Articulate brachiopods' mode of life. They tended to live in shallow marine conditions (up to 500 m but may go down to 6, 000m). Modern forms live in cool - temperate waters around the Pacific (Japan, S. Australia, New Zealand, N. Atlantic and W. Scotland). As there are modern day equivalents we know their environments and so they are good palaeoenvironment indicators (index fossils).

Index fossils etc. Define an index fossil: A fossil that is restricted to a particular palaeoenvironment. Corals mare perhaps the best index fossils. The most common question regarding Brachiopods is how to tell the difference between them and Bivalves. We will cover this next when we look at Bivalves.

GEOLOGICAL HISTORY: Brachiopods are a long-lived Phylum ranging from the Cambrian to Present. They were very common in the Palaeozoic and slightly less so in the Mesozoic but still remain important. In the Present not many forms are left with approximately 70 Genera. Over 2500 fossil Genera are known. The largest were found in the Cambrian (370 mm).