Pen Shells of the Pinnidae Family

One Pen Shell of the Pinnidae Family can be found in this website:

Wrinkled Pen Shell, Pinna rugose. A representative of the of the Pinnidae Family of Pen Shells.

Phylogeny: Pen Shells of the Pinnidae Family are bivalve mollusks in the Ostreida order. There are three superfamilies in this order: Ostreoidea, Pinnoidea, and Pterioidea. The Pinnidae Family is the only family in the superfamily Pinnoidea. The Pinnidae Family is moderate in size, with no subfamilies, three genera, and sixty-three species. Shells in this Family are also commonly known as Fan Shells or Pinnids.

Description: Pen Shells are shaped like a long triangle or wedge that is moderately inflated. They are equivalve (both valves equal in size and shape). There is a significant gap between the valves at the much wider posterior end and a much smaller anterior gap, through which the byssal threads pass. They have a long straight hinge that lacks teeth.  The shells are thin and flexible, unless they dry out and become brittle. The exterior may be smooth or sculpted with short spines or radial undulations. These shells tend to be dully-colored. The interior will have nacreous areas that are indicative of the species. Some species of Pen Shells are among the largest of the bivalves, reaching 95 cm (37 inches) in length.

Habitat and Distribution: Pen Shells bury their anterior end in sand, mud or gravel, and attach themselves to the substrate via byssus. They live in the intertidal zone, and at depths up to 200 m (642 feet). They are found worldwide in subtropical to tropical seas. At least eight species from this family are found in Mexican waters.

Natural History: Pen Shells are suspension feeders, filtering plankton and fine detritus from the surrounding water. They are preyed upon by shorebirds, crabs, carnivorous mollusks and fish. Pen Shells are gonochoric and reproduce sexually through broadcast spawning. They produce pearls of moderate value. Some species produce “sea silk”, a material made from the byssus. Sea silk has been utilized in the manufacture of clothing for many centuries. Clothing made from sea silk has a golden hue and was greatly valued during ancient times. Pen Shells are edible and are the target of artisanal and small commercial fisheries in Asia and the South Pacific.