Noble pen shell

Pinna nobilis

ORDER

Pterioida

FAMILY

Pinnidae

TAXONOMY

Pinna nobilis Linnaeus, 1758, Mediterranean Sea.

OTHER COMMON NAMES

English: Fan shell, Mediterranean pen shell; French: La Grande Nacre, jambonneau; German: Grosse Steckmuschel; Spanish: Gran nacra.

PHYSICAL CHARACTERISTICS

Shell is narrowly elongated, compressed, and triangular in shape; umbo at pointed anterior end, bluntly flattened or rounded at gaping posterior end. Surface is fragile, sculptured with dense erect scales in younger specimens that erode to smooth areas in older parts of large adults. Exterior is light tan to orange in color; interior lightly nacreous in anterior portion. P. nobilis is the second largest living bivalve, growing to 35.5 in (90 cm) in length. Soft body with pallial organ; secretes long strong stalk of gold or brown byssal threads exiting shell ventrally near umbo.

DISTRIBUTION

Mediterranean Sea.

HABITAT

Infaunal, half-buried vertically in sand, mud, gravel, or sea-grass, in waters up to 197 ft (60 m) in depth. Shells form an important hard substrate for biocoenotic aggregations in soft-bottom habitats, especially mollusks and sponges, thereby increasing overall local species richness.

BEHAVIOR

The pallial organ actively clears broken shell and other debris from mantle cavity. Commensal crustaceans live outside the valves, retreating into mantle cavity when threatened; crab's entry stimulates pen shell to close, thereby protecting the crustacean.

FEEDING ECOLOGY AND DIET

Filter feeder.

REPRODUCTIVE BIOLOGY

Protandric hermaphrodite; broadcast spawner. Life span about 20 years.

CONSERVATION STATUS

Not listed by the IUCN. Overcollected by divers; considered endangered throughout the Mediterranean. Protected by national laws in Spain, France, and other coastal European countries.

SIGNIFICANCE TO HUMANS

Human food source (adductor muscle). The historical use of natural pearls, both nacreous and porcelaneous (orange to black), is documented as far back as the third century B.C. Gold-colored byssus threads as long as 2 ft (61 cm) were used in weaving textiles since Roman times, including cloth for gloves, shawls, stockings and cloaks. The mythological Golden Fleece was probably spun from byssus threads of this bivalve.