In the last few decades there has been a noticeable decrease in the population of the Mediterranean's endemic and largest bivalve, the noble pen shell. Pinna nobilis is a successive hermaphrodite with asynchronous gametogenesis that prevents self-fertilization. The individual becomes sexually mature between 1 and 2 years, after which the spawning season is visible once a year with rising of the sea temperature in late spring and with peaking during the summer months. The fertilisation is external. After the larval phase, which lasts approximately ten days, the individual is situated at the sea bottom. Juveniles are fragile and sensitive and that's why they are facing a diverse collection of threats, such as predators, poor food supply or being covered by the sediment. The individual is considered as an adult when it reaches the size of 10 centimeters. With growth and aging it becomes more and more resistant to external threats. The noble pen shell is a long-living bivalve with a lifespan of up to 45-50 years. The aim of this thesis is to sum up so far known information about stages of life cycle and developmental biology. Furthermore it may be used to point out the importance of correct care, protection and potential restocking of the critically endangered and biologically as well as ecologically important species.