Wrinkled Pen Shell, Pinna rugosa

Wrinkled Pen Shell, Pinna rugosa. Size: 16 cm (6.3 inch) x 5.5 cm (2.2 inches). Shell collected from within the estuary of the Magdalena Bay complex, Baja California Sur, October 2018.

The Wrinkled Pen, Pinna rugosa (G.B. Sowerby I, 1835), is a bivalve mollusk that is a member of the a Pinnidae Family of Pens. They are also known as the Rugosa Pen and in Mexico as hacha larga, nacre rugosa, and pina hacha larga. The shell is long, triangular, and thin with radiating folds that form scales or short spines adorn the outside. The interior of both valves have two nacreous lobes, separated by a narrow groove. are long, triangular, and thin. Their exterior is yellowish brown to dark brown in color. The Wrinkled Pen Shell reach a maximum of 43 cm (17 inches) in length and  20 cm (8 inches) in height.

Wrinkled Pens are found in shallow mudflats in the intertidal zone to depths up to 100 m (330 feet). They range from the San Ignacio Lagoon, Baja California Sur to Peru, including the Clipperton and Galapagos Islands and throughout the Sea of Cortez.