Pinna nobilis, whose common name is the noble pen shell or fan mussel, is a large species of Mediterranean clams.
It reaches up to 120cm of shell length. It produces a rare manganese-containing porphyrin protein known as pinnaglobin.
As with other members of its genus, Pinna nobilis hosts symbiotic shrimp which live inside its shell. It is believed that when it sees a threat, the shrimp warns the host, perhaps by retracting its claws or even by pinching. The clam then closes shut. It has been demonstrated that the shrimp has a similar filter-feeding diet to its host and the relationship is likely.
In 2016, there was an outbreak of a disease that caused the mortality of 99% of its population in Spain.
The cause of the disease is a newly discovered pathogen, Haplosporidium pinnae and it is posing a serious threat to the survival of the species.
By 2019, mortality spots had been detected in Greece, Croatia, Turkey, Tunisia, France and Morocco.
In the past, Pinna nobilis has been threatened with extinction, due in part to fishing, incidental killing by trawling and anchoring,
and the decline in seagrass fields; pollution kills eggs, larvae, and adult mussels. The pathogen, which is still present in the environment,
will make recovery a challenge, so continuing declines are expected. The percentage of population size reduction over the last ten years is over 80%.
In December 2019, Pinna nobilis has entered the IUCN Red List as critically endangered
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