Generalized Brachiopod Classification
Brachiopods are the official state fossil of Kentucky https://www.uky.edu/KGS/education/state-fossil-brachiopods.php. They are a phylum of life. Phylums are a very large-scale rank of organisms with a similar body plan. Brachiopods are classified into sequentially more specific classes, orders, families, genera, and species, based on shape and features of their shells. Brachiopods used to be classified into two broad ranks; inarticulate and articulate, which were then further subdivided. These terms are now replaced by scientific terms for the subphylums they represent, but the terms are still useful for informally describing the basic subdivisions of brachiopods.
The general name for types of brachiopods which have two articulated valves. Articulation of the valves occurs along tooth-and-sprocket structures along the hinge between the two valves, as well as through muscles which attach to both valves. Articulate brachiopods commonly have valves composed of hard, calcium carbonate minerals (which may be replaced by other minerals when fossilized). Articulates include the majority of fossil brachiopods.
Scientifically, articulate brachiopods are in the subphylum Rhynconeliformea, which is divided into two broad classes; Rhynchonellata and Strophomenata.
Rhynchonellata contains the orders:
Strophomenata contains the orders:
The general name for types of brachiopods in which the two valves of the brachiopod are held together by muscles alone, and not by a tooth-and-sprocket hinge mechanism. Inarticulate brachiopods commonly (but not always) have valves composed of phosphate, organic material and chiton (like the material in human fingernails), rather than calcium carbonate, which is common in articulate brachiopods. Inarticulates represent only a small amount of the total number of fossil brachiopods. Inarticulates were more common than articulate brachiopods in some depositional environments in the past, and were the dominant type of brachiopod during the Cambrian Period.
Scientifically, inarticulate brachiopods belong to the sub-phylums Craniformea (having calcium carbonate shells) and Lingulata (having phosphatic shells). Lingula is a modern example of Lingulata inarticulate brachiopods.
Craniformea contains only one class, Craniata, which contains the orders Craniida, Craniposida, and Trimerilida. These orders do not contain fossil brachiopods commonly found in Kentucky.
Lingulata contains the orders Acrotretida, Lingulida, and Siphonotretida, but only Lingulida contains fossils commonly found in parts of Kentucky.