M-650 PEN SHELL, Atrina rigida or A. serrata

A large, brown fan-shaped bivalve that anchors itself down into the sand with an enormous tuft of silk byssus threads. Historians suggest that the “Golden Fleece” was made from Pen Shell silk. This triangular clam, which is normally three-quarters buried, uses the long fingerlike foot to shove bits of broken shell and gravel away from its orange mantle. Many specimens contain commensal crabs, Pinnotheres maculatus. Size: 12-20 cm.