English: Martesia striata (Linnaeus, 1758) - "wood piddock" & borings in driftwood 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.

Seen here is a woodground - a piece of driftwood that washed ashore onto a marine beach. The holes were made by boring bivalves: Martesia striata (nicknamed "wood piddocks"). One light-colored Martesia shell is still occupying a drillhole. Martesia striata is also known to make excavations in firmgrounds and hardgrounds.

Classification: Animalia, Mollusca, Bivalvia, Heterodonta, Myoida, Pholadidae

Locality: Lighthouse Point beach, southern shore of the eastern tip of Sanibel Island, Gulf of Mexico coast of southwestern Florida, USA

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More info. at:

en.wikipedia.org/wiki/Pholadidae