They include oysters, crabs of great size, and a small mussel, found in enormous numbers.
The sea mussel (Mytilus edulis) belongs to the second order of the class Lamellibranchia, namely the Filibranchia, distinguished by the comparatively free condition of the gillfilaments, which, whilst adhering to one another to form gillplates, are yet not fused to one another by concrescence.
The pearl mussel was formerly used as bait in the Aberdeen cod fishery.
The sea mussel is scarcely inferior in commercial value to the oyster.
In Scotland and Ireland the pearl mussel fishery was also of importance, but has altogether dwindled into insignificance since the opening up of commercial intercourse with the East and with the islands of the Pacific Ocean, whence finer and more abundant pearls than those of Unio margaritiferus are derived.