Chonetes sp. - fossil brachiopod in sandstone in the Mississippian of Ohio, USA.

Brachiopods are sessile, benthic, filter-feeding, marine invertebrates. They first appear in Cambrian rocks and were abundant in Earth's oceans throughout the Paleozoic. They were also common in Mesozoic oceans, but are scarce in modern oceanic biotas. Brachiopods have two shells, called valves, that are usually calcareous (made of calcite - CaCO3 - calcium carbonate). Each shell of a brachiopod is bilaterally symmetrical, unlike each shell of a bivalve (clam).

The small brachiopod shown here is a chonetid, preserved as a mold (the calcareous shell is gone - dissolved away). The yellowish-brown staining is limonite, an iron oxide mineral.

The small white object in the lower part of the picture is a fragmentary fossil fish bone.

Classification of brachiopod: Animalia, Brachiopoda, Articulata (also known as Rhynchonelliformea), Strophomenata, Productida, Chonetidae

Stratigraphy: float from the upper Vinton Member, upper Logan Formation, ~middle Osagean Stage, upper Lower Mississippian