Family Pholadidae

Shell size to 65 mm; shell shape variable, usually pear-shaped, thin. Sculpture of fine concentric, denticulate ridges anterior to oblique groove; ridges smooth posterior to groove. Very destructive wood borer. Anterior accessory plate (mesoplax) nearly as wide as narrow, circular or squarish with rounded edges, with sculpture of fine wrinkles. Juveniles circular in outline. The Striate Piddock uses the anterior end of its rough shell to bore through wood. Piddocks use a semi-circular motion to "drill", creating a long, cylindrical hole that is occupied for life by the animal. When crowded in a piece of driftwood, piddocks may become reproductively active at small size. To collect their shells, look for "Swiss cheese-like" driftwood with the characteristic boreholes indicative of their presence. Supplementary images show piddocks in their driftwood habitat, and the last image is a detail of the apophyses, attachment structures for the paired foot muscles, which are responsible for the rocking drilling motions.

Shell size to 20 mm; shell shape variable, usually pear-shaped, thin. Sculpture of fine concentric, denticulate ridges anterior to oblique groove; ridges smooth posterior to groove. Anterior accessory plate (mesoplax) very distinctive, longer than wide, tear-drop- or heart-shaped, sculpted with fine growth lines. Very destructive wood borer, found in drift wood and floating logs.

Shell size to 180 mm; shell light, thin, elongate. Sculpture of concentric ridges and strong radial ribs. Scale-like projections form at intersections of ridges and ribs. Pair of spoon-shaped structures under umbones, called apophyses, are points of attachment of foot muscles. Color pure white, seldom with delicate pinkish internal coloration. Borer in mud bottoms in protected bays. After storms, loose valves wash on Gulf beaches near inlets.

Shell size to 70 mm; shell elongate, thin, fragile. Valves widely gaping. Sculpture of radial ribs and concentric ridges. Anterior ridges with scale-like projections. Radial ribs weak or lacking posteriorly. Color dull-white. The Atlantic Mud Piddock bores into hard clay and soft rock. It will settle as a larva onto the host rock, and will grow as it bores into it. The resulting borehole is conical (with the narrow end toward the rock surface), and the piddock ends trapped inside the rock for life.