EUROPA – Underwater flora and fauna,The noble pen shell

The noble pen shell (Pinna nobilis) is an endemic species of the Mediterranean, the largest bivalve in the Mediterranean Sea and among the largest bivalves in the world. It usually grows between 30 and 50 cm but can reach lengths of up to 120 cm and live to be around fifty years old. It lives in sandy bottoms and seagrass meadows, from the surface up to about sixty meters in depth. It uses the rear pointed end of the shell to bury itself partially into the sediment and attach to it using numerous so-called byssal threads. The other end is fan-shaped, ranging from light brown to reddish color. The two shells are identical and the pen shell opens them only about a centimeter to filter the sea water and collect plankton and organic particles from it. It can filter hundreds of liters of sea on a daily basis. If it feels threatened, it will close its shells tightly. The little crab (Nepinnotheres pinnotheres), which often lives inside it, can also warn it of danger. The noble pen shell has always been a prized bivalve. Its durable byssal threads were used to make royal clothing, ornaments and gloves that shone like gold in the sun. Due to their grand size and smooth iridescent interior structure, its shells were used as an ornament. In many regions, it was a traditional delicacy. Sometimes, small irregular pearls were found inside the pen shells. With the increase in awareness of the need for its conservation, as well as its designation as a strictly protected species, pen shell populations in many areas of Croatia have developed dense settlements since the beginning of the 21st century. During the autumn of 2016, Spain recorded a death of this species. It was probably caused by a disease, which spread to the Croatian part of the Adriatic Sea in 2019, resulting in its mass mortality. The exact cause of this disease is unknown and it spread to the entire Mediterranean Sea, almost leading to the extinction of the noble pen shell as a species. At the beginning of 2024, only about 20 living specimens were known in the seabed of Croatia. However, their survival and the discovery of live specimens in some other areas of the Mediterranean, such as the Marble Sea, offer hope that noble pen shell will again spread in our seabed. Dr. sc. Ante Žuljević