Pinna rugosa is a species of pen shell, a large, fan-shaped bivalve mollusk belonging to the family Pinnidae. These marine bivalves are known for their elongated, triangular shells that are often anchored upright in sandy or muddy substrates by strong byssal threads. Elongated and wedge-shaped, with a broad opening at one end and a tapered, pointed end buried in sediment. Characterized by rugose (wrinkled or ridged) sculpturing, giving it a rough appearance. A filter feeder, extracting plankton and organic material from the water.