The exhibit obtained in 1923 was found in the Adriatic Sea. It is the noble pen shell (Pinna nobilis), a representative of the class Bivalvia (bivalve molluscs) and the family Pinnidae. This endemic Mediterranean species is one of the region’s largest molluscs; its shell sometimes grows up to 1.2 meters (usually 30–50 cm). The shells are thin-walled, fragile, triangular, and have a pearlescent interior; in rare cases, pearls form within them. The mollusc is found at various depths, from half a meter to about sixty meters. It attaches itself to the seabed substrate with byssal threads at its pointed end. Byssus is a silk–like filament, composed of keratin and other proteins, produced by special glands of the mollusc.
The noble pen shell, like other bivalve molluscs, feeds on microplankton by filtering water. Inside the Pinna shells, the shrimp Pontonia pinnophylox or the crabs Nepinnotheres pinnotheres often live. These crustaceans, like the pen shell, feed by filtering water. It is believed that they somehow warn their host of danger, causing the mollusc to close.
The noble pen shell has been used for food for thousands of years, and the byssal threads are used to extract the so-called sea silk. The first knowledge of sea silk dates back about three thousand years. The processing, dyeing, spinning, and weaving of byssal threads is a complex, labor–intensive process. Sea silk fabric was a symbol of the highest status for people. It is said that Nefertiti and important representatives of Ancient Greece and the Roman Empire wore it. It has been found in pharaohs’ tombs. There is also an inscription about sea silk on the Ptolemy’s Rosetta Stone. In modern times, the production of sea silk has practically disappeared.
The noble pen shell (Pinna nobilis) has been listed as a critically endangered species in the International Red List since 2019. These molluscs are harmed by excessive fishing, pollution, and the loss of natural habitats. Collecting them is prohibited, but the ban is often ignored—pen shells are gathered for food or for their decorative shells. Since 2016, the noble pen shell has faced an even greater threat. The molluscs are being destroyed by the single-celled parasite Haplosporidium pinnae, which is carried by surface water currents throughout the entire Mediterranean Sea. It has been determined that the parasite damages the mollusc’s digestive system. How the parasite entered the Mediterranean Sea is unknown. It has been established that molluscs of the related genus Atrina do not become infected with this parasite. Scientists are making tremendous efforts to stop the spread of the parasite and protect the mollusc from extinction. In order to save the species, Pinna nobilis is even being transferred to aquariums in some locations.
