PEN SHELL (pinna nobilis)

In Jule Verne's novel "Twenty Thousand Leagues Under the Sea" the whole staff is dressed in sea silk. Hardly anybody knows that this is not pure fiction.
The pen shell has a byssus gland that secretes byssus, an organic matter that hardens in contact with water and forms threads that help fasten the valves to the base. This is the raw material for the sea byssus. But only kings could afford to wear cloths from sea silk. 4000 shells had to be killed to get 1 kg of silk.
Also the meat is very tasty; no wonder that this species had to be protected in 1994 and collecting and trading with this species is strongly forbidden.
Pinna nobilis is fan – shaped, up to 45 cm long, red – brown shellfish. Its habitat is in the coastal region, standing upright in sandy or overgrown by sea – flowering plants sea bottoms, on depth 2 – 30 m. Population density is rarely more than 1 item on 10 m2 of the bottom. Its shell is often overgrown by algae, sponges, tubeworms, moss animals or other small sedentary animals. Pinna nobilis is a endemic species of the Mediterranean Sea and it is distributed along the Adriatic coast. It is the largest shellfish in the Mediterranean and its shell were used as a popular souvenir and decoration.
Recently marine biologists found out that there is a strong correlation of oxygen isotopes in the shell and the temperature of the water. Since the pina nobilis lives up to 40 years, the shell gives us information about the temperature some decades ago. The good thing is, that the shell has not to destroyed for such an examination.