Phylum: Brachiopoda
The Phylum Brachiopoda, which appeared in the Lower Cambrian Period, was one of the most abundant Paleozoic fossil phyla with over 30,000 species. That number has now dropped to 280 living species. The animal has two unequal valves which makes the brachiopod’s exoskeleton. They have a tiny heart with a poorly-developed circulatory system. Their respiratory and digestive systems are very primitive. The nervous system is developed. The brachiopods have separate sexes and are not colonial animals. They are sessile (stationary on the seafloor) animals attached to the seafloor by a pedicle, or half-buried within the muddy sediment. Others were propped up in the mud by fragile spines. There are two classes in this phylum: Inarticulata and Articulata.
Class Articulata (lower Cambrian to Recent)
This class of brachiopods is highly evolved and is the most common class, usually having a calcareous shell, hinged with a tooth socket arrangement for opening the valves. There are four common orders you should be able to recognize by examining the fossil’s hinge line and the valves. The valves are either concave (curving inward) or convex (curving outward).
Order Orthida. The hinge line is shorter than the width of the valve. Both valves are convex. The following genera belong to the order Orthida; Enteletes, Rhipidomella, or Schizophoria.
Order Strophomenida. The hinge line goes the full width of the valve. The valve is wider than long; one valve is convex, and the other is concave. The following genera belong to the order Strophomenida: Derbyia, Juresania, Meekella, Mesolobus, Reticulatia, Echinaria, Chonetinella, or Neochonetes.
Order Spiriferida. The valves are biconvex with the hinge line being the full width on the spirifer, but not on other genera. The following genera belong to the order Spiriferida: Neospirifer, Punctospirifer, Hustedia, and Composita.
Order Terebratulida. The valves are convex and teardrop-shaped. Dielasma and Beecheria are common genera in this order.
This class of brachiopods is highly evolved and is the most common class, usually having a calcareous shell, hinged with a tooth socket arrangement for opening the valves. There are four common orders you should be able to recognize by examining the fossil’s hinge line and the valves. The valves are either concave (curving inward) or convex (curving outward).
Order Orthida. The hinge line is shorter than the width of the valve. Both valves are convex. The following genera belong to the order Orthida; Enteletes, Rhipidomella, or Schizophoria.
Order Strophomenida. The hinge line goes the full width of the valve. The valve is wider than long; one valve is convex, and the other is concave. The following genera belong to the order Strophomenida: Derbyia, Juresania, Meekella, Mesolobus, Reticulatia, Echinaria, Chonetinella, or Neochonetes.
Order Spiriferida. The valves are biconvex with the hinge line being the full width on the spirifer, but not on other genera. The following genera belong to the order Spiriferida: Neospirifer, Punctospirifer, Hustedia, and Composita.
Order Terebratulida. The valves are convex and teardrop-shaped. Dielasma and Beecheria are common genera in this order.
Class Inarticulata (lower Cambrian to Recent)
No hinging structure; the valves are opened and closed by complex muscles. The shell generally is not calcium carbonate. Fossil records are usually preserved by the carbonization process. Usually only one valve is preserved, and it has no teeth or sockets. Common inarticulate brachiopods found in Kansas are Lingula, Crania, and Orbiculoidea
No hinging structure; the valves are opened and closed by complex muscles. The shell generally is not calcium carbonate. Fossil records are usually preserved by the carbonization process. Usually only one valve is preserved, and it has no teeth or sockets. Common inarticulate brachiopods found in Kansas are Lingula, Crania, and Orbiculoidea