What is stiff pen shell?

Stiff pen shell (Atrina rigida) is a species of bivalve mollusk that is commonly found in the temperate and tropical waters of the Atlantic Ocean, ranging from Massachusetts to Brazil. They are also known as the giant pen shell due to their large size, and can grow up to 60 cm in length.

They are filter feeders, and primarily feed on plankton and other small organisms that they filter out of the water column. They are typically found in shallow waters up to a depth of 100 meters, and can be found in areas with sandy or muddy bottoms.

Stiff pen shells have an elongated, triangular shell with distinct ridges and grooves, which gives it a stiff appearance. They are typically brown or black in color, with a white interior.

Their shells are highly valued for their ornamental and decorative value, and are often used in jewelry and crafts. However, overfishing and pollution have led to a decline in population numbers in some areas, and stiff pen shells are now considered a threatened species in some parts of their range.