The Saw-tooth Pen Shell
The Saw-tooth Pen Shell, Atrina serrata (G.B. Sowerby 1, 1825), is one of three species of Pen Shells regularly found strewn on our beaches, particularly after winter storms or following environmental disturbances. Its shell is similar to the Stiff Pen Shell, Atrina rigida, but is thinner, showing lighter color. It also differs by the finer, smaller scale-like projections regularly deployed along about 30 radial ribs. This is the most distinctive of the three local species of Pen Shells in the genus Atrina.
The photo on right shows a Saw-tooth Pen Shell in the shell museum's "Live Tank." The bivalve is lying on its side (in nature it would assume a vertical position, half-buried in the sand) and the incurrent aperture (water gets in for feeding and respiration) is on right and excurrent ("used" water is expelled) on left. The bivalve can "zip-up" the mantle edges to regulate water flow. Photos by José H. Leal.