Sawtooth Pen Shell
Atrina serrata Sowerby, 1825
The spines of the Sawtooth Pen Shell
The clams of the Pen (Pinnidae) family are very distinctive in appearance, having two large wedge- or fan-shaped halves, or valves; the dorsal margin of each valve is straight, the ventral margin rounded, and the posterior gaping. Some species of the Pinnidae family grow to a length of more than two feet.
The bivalve lives near shore, partially buried, in sand flats and grass beds. The clam attaches itself to hard objects under the surface of the sand using protein threads (called the “byssus”). The narrow part of the “fan” sticks into the sand, and the flared part sticks out into the water above the sediment.
Pen Clams close their shells by flexing their adductor muscles and actually bending the shell. — Most bivalves use the hinge of their shells for opening and closing, rather than bending.
The Sawtooth Pen Shell is 8 to 12 inches long. Its fragile, translucent valves are yellowish-brown on the exterior. The inside surface of the bivalve halves is a lovely, iridescent, peacock-like play of color, more evident when the shell is wet.
Atrina serrata has a delicately sculpted surface with little, sharp, tooth-like spines on its approximately thirty closely-spaced rows of ribs.
The Sawtooth Pen Shell may be found from the North Carolina coast to Texas and the West Indies.