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the pen shell (pinna nobilis) ................................................................................................................................................................................................
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| the pen shell (pinna nobilis) - august 2002 - the swedish naturalist carl linnaeus, also known as carl von linné or carolus linnaeus (1707-1778) first described the species in 1758. it is an endemic species of the mediterranean, belonging to the family of pinnidae. this large, brown fan-shaped bivalve shellfish, one of the largest in the world, can reach a breadth of 1,2 metres. its habitat is in the coastal region, on the shoals that are either sandy or overgrown by sea-flowering plants. it is found mainly in south italy /sardinia, but also in france /around the mediterranean islands (corsica ...), on the coasts of yugoslavia, in north-africa, etc. --- byssus threads the pen shell has a byssus gland that secretes byssus, an organic maner that hardens in contact with water and forms threads that help fasten the valves to the base. the fan mussel lives half buried in the sediment where it finds nourishment and shelter. like many other organisms it remains anached to the same substratum in the same place, almost stationary, to the end of its life. it can, however, use its foot to move slowly and in limited fashion. this means that the fan mussel can be found at different depths depending on age. during the larva stadium it spends its life swimming freely. the young individuals being found near the surface, while the older individuals live at a depth of approximately 40 metres. --- the decline in populations threatened with extinction for some forty years - it is partly due to the decline in the posidonia oceanica seagrass meadows. trawling, anchoring of yachts, various pollutants, sea resort and other developments, as well as unauthorized fishing by certain divers, have all contributed to accelerating the decline of this species. the decline in the seagrass has serious implications for the fan mussel whose highly specific ecology and metabolism renders its reproduction difficult. --- reproduction the eggs mature and the larvae develop in the open seas. then, made heavy by a thin calcitic shell following its planktonic phase, the larva falls to the bottom where it attaches itself. at this stage it measures approximately 2 cm and has a transparent and fragile shell, which leaves the animal prey to numerous predators, such as octopus, sea bream, etc. the mortality rate at this stage is therefore high.
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 the pen shell (pinna nobilis) with tuft of silky byssus threads  fishing of the pinna nobilis  the pen shell is dug into the oozy-sandy base with a third of its valve by its sharp pointed end  pinna nobilis, linné, 1758 |
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