The noble pen shell is a bivalve mollusk that can reach a size of about 3.3 feet. Like all bivalves, it is characterized by a shell composed of two parts, called valves, joined by a hinge. In the case of the noble pen shell, the two valves are symmetrical and shaped like elongated triangles ending in a rounded edge.

The noble pen shell is a bivalve endemic to the Mediterranean sea. Just like the seagrass meadows of Posidonia where it makes its home, it can be found from shallow waters down to depths of about 165 feet, as long as there is enough light.

The noble pen shell lives on sandy bottoms and mainly in Posidonia seagrass meadows, where it is buried in the sediment up to about one-third of its height or even half in some cases.

The noble pen shell feeds on living particles (plankton) or dead organic matter suspended in the water, filtering it through its gills. The water current is generated by the movement of tiny cilia.

The noble pen shell is hermaphroditic and its reproduction occurs through alternating releases of male and female gametes. Fertilization happens in open water, giving rise to larvae that, after a planktonic stage, settle on a surface or anchor in the sediment to develop and transform into a bivalve.

At lengths of 3.3 feet or more, the noble pen shell is the largest bivalve mollusk in the Mediterranean ! Alongside the giant clam, it is one of the largest bivalve mollusks in the world !

If it falls on the seabed, the noble pen shell can right itself using its foot.

The noble pen shell is a protected species: it appears in the decree of November 26, 1992 (published in the Official Journal No. 15 of January 19, 1993), which lists the protected species of marine fauna.

Nevertheless, the noble pen shell is threatened by the decline of Posidonia seagrass meadows and by careless anchoring of boats !

The noble pen shell is listed as many other marine species within The IUCN Red List of threatened species. The noble pen shell appears in the IUCN Red List since 2019 within the category Critically Endangered !

Large adult noble pen shells are easy to spot inside Posidonia meadows, but with attention you can also notice smaller specimens. A golden rule when exploring these meadows: maintain perfect buoyancy and take care with your fin movements to avoid knocking over a noble pen shell !

It is sometimes possible to find small crustaceans such as tiny crabs or shrimp inside the shell of the noble pen shell, where they find both food and shelter without disturbing their host.