Kingdom – Animalia
Phylum – Molluska
Class – Bivalvia
Order – Pterioida
Family – Pinnidae
Genus – Pinna
Species – P. nobilis
Pinna nobilis (also called the noble pen shell) is the largest shellfish endemic to the Mediterranean. Its habitats include seagrasses of the species Posidonia oceanica and Cymodocea nodosa (see descriptions of these two species on our website).
The pen shell usually favours closed, protected bays with water depths up to 40 m. The main factors that characterise the habitat of the Pinna nobilis are suitable lighting, clean water, low seasonal variations in salinity (3.4 to 4%), moderate temperatures (7 to 28° C) and a uniform, slow flow with enough nutrients.
Noble pen shells are filter feeders, filtering planktonic organisms from 6 litres of water every hour. As a hermaphrodite, it produces male and female germ cells, which it alternately releases in the water from June to August. After fertilisation, free-swimming larvae are developed, which, after a few days and once they have formed a thin calcareous shell, drop to the ocean floor. Now the shell produces the first byssus threads and grows into place. In the first year it reaches a size of 10 to 15 cm, fully grown, the shell can grow up to a size of 120 cm and reach an age of 20 years (de Gaulejac 1995, Vicente 2000, Siletic 2004).
The byssus of the noble pen shell is a bundle of fine, tear-resistant fibres which are formed by the byssus gland in the foot of the shell. The surface is smooth, the diameter of this fibre is comparable to other animal and vegetable fibres. At the moment of formation of fibres, the movable, about 9 cm long foot forms a channel through which the protein secretion of the gland flows. With the toe of the foot the secretion is applied on a suitable location – roots of the seagrass, sand, stones. In contact with the water, the secretion hardens to the byssus fibre.
The silky fibres can reach lengths of 20cm and this is the raw material from which sea silk is produced
This species has been deemed endangered and is under great threat from anthropogenically produced pollution, recreational diving but most of all from bottom trawling and other destructive fishing methods.