Fan Mussel (Pinna nobilis)

The Fan Mussel, also called Pen Shell and endemic to the Mediterranean, resides offshore, nestled in soft-sediment areas. It plays host to symbiotic shrimp, which live inside the shell and offer alerts upon sensing threats1. 

A devastating mass mortality event has occurred since 2016, caused by a harmful parasite and bringing about drastic population declines. Previous threats via illegal fishing, habitat loss, and climate change hadn't previously affected numbers so drastically. Because of these threats, the Fan Mussel is now critically endangered, with anticipated continued declines.