Dosinia discus (Reeve, 1850) - disc dosinia clam shell (modern) from Florida, USA.

Bivalves are bilaterally symmetrical molluscs having two calcareous, asymmetrical shells (valves) - they include the clams, oysters, and scallops. In most bivalves, the two shells are mirror images of each other (the major exception is the oysters). They occur in marine, estuarine, and freshwater environments. Bivalves are also known as pelecypods and lamellibranchiates.

Bivalves are sessile, benthic organisms - they occur on or below substrates. Most of them are filter-feeders, using siphons to bring in water, filter the water for tiny particles of food, then expel the used water. The majority of bivalves are infaunal - they burrow into unlithified sediments. In hard substrate environments, some forms make borings, in which the bivalve lives. Some groups are hard substrate encrusters, using a mineral cement to attach to rocks, shells, or wood.

The fossil record of bivalves is Cambrian to Recent. They are especially common in the post-Paleozoic fossil record.

The hole in this dosinia clam shell is a predatory boring. Borings are examples of trace fossils - any indirect evidence of ancient life. Other categories of trace fossils include burrows, tracks, trails, footprints, and bitemarks. Traces (also called ichnofossils) record the behavior of ancient organisms. Trace fossils are given scientific names in a similar style as living organisms or body fossils.

Predatory drill holes in shells are known from the latest Precambrian to the Holocene. The beveled boring seen here was made by a naticid gastropod (moon snail).

Classification: Animalia, Mollusca, Bivalvia, Heterodonta, Venerida, Veneridae