Pinna is a genus of bivalve molluscs belonging to the family Pinnidae. The type species of the genus is Pinna rudis. The most extensively studied species in the genus is P. nobilis, a Mediterranean pen shell which was historically important as the principal source of sea silk.

Description

These pen shells can reach a length of about 80 - 90 cm. They are characterized by thin, elongated, wedge-shaped, and almost triangular shells with long, toothless edges. The surface of the shells shows radial ribs over their entire length. Pinna is distinguished from its sibling genus Atrina by the presence of a sulcus dividing the nacreous region of the valves, and the positioning of the adductor scar on the dorsal side of shells. These bivalves most commonly lie point-first on the sea bottom in which they live, anchored by a net of byssus threads.

Distribution

Species in the genus Pinna are geographically widespread. This genus is very ancient, going back up to the Carboniferous period. It is especially represented in Jurassic and Cretaceous fossils.

Species

According to the World Register of Marine Species, extant species in the genus Pinna are: The following species are only known from the fossil record:

Nomen nudum

Nomen dubium

Synonyms