Pinna nobilis
Pinna nobilis, common name
Common name
A common name of a taxon or organism is a name in general use within a community; it is often contrasted with the scientific name for the same organism...

 the "noble pen shell" is a species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 of pen shell, a large marine
Marine (ocean)
Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology...

 bivalve mollusc in the family Pinnidae
Pinnidae is a family of large saltwater clams sometimes known as pen shells. They are marine bivalve molluscs in the order Pterioida.The shells are fragile and have a long and triangular shape, and in life they are anchored in sediment using a byssus...

, the 'pen shells'.

The bivalve shell can grow almost 91 cm (3 feet) long, and its shape is variable. Like all pen shells it is relatively fragile. It attaches itself to rocks using a strong "cable" composed of many silk-like hairs, or byssus, fibre the shell produces. The inside of the shell is lined with brilliant mother-of-pearl.

This species is the origin of sea silk
Sea silk
Sea silk is an extremely fine, rare and valuable fabric produced from the long silky filaments or byssus secreted by a gland in the foot of several bivalve molluscs by which they attach themselves to the sea bed....

, which was made made from the byssus
Byssus means both a silky filament by which certain molluscs attach themselves to hard surfaces, and a rare fabric, also called sea silk and its fibre source.-Word:...

 of the animal. It is endemic to the Mediterranean Sea
Mediterranean Sea
The Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by North Africa, and on the east by the Levant...

, and lives offshore down to a depth of 20 metres.

Unfortunately, in recent years, Pinna nobilis has become threatened with extinction, partly due to overfishing, the fact that the mollusc is edible, the decline in seagrass
Seagrasses are flowering plants from one of four plant families , all in the order Alismatales , which grow in marine, fully saline environments.-Ecology:...

fields, and pollution.
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