Adula simpsoni (Marshall), a bivalve associated with Whale skulls in the North Sea.

The crew of a Scarborough trawler struggle to remove the rotting carcase of a 40ft whale brought up in the trawl; remains of whales and dolphins are frequently seen by trawler crews. Photo donated by Malcolm Ward.

The crew of a Scarborough trawler struggle to remove the rotting carcase of a 40ft whale brought up in the trawl; remains of whales and dolphins are frequently seen by trawler crews. Photo donated by Malcolm Ward.

The rotting or skeletonised remains of whales and dolphins are frequently brought up in the nets of trawlers working round the British Isles. However, it is only in recent years that biologists have discovered that the remains of dead whales, known as whale falls, attract a series of activities of other marine species, that not only reduce the carcase to its bony framework, but which then begin to colonise, and in some recently discovered polychaete worms, also extract nutrients from, its bones.

In the eastern North Atlantic and around the north of Scotland into the North Sea, however, a small bivalve of the mussel family Mytilidae, has long been known to be associated with the remains of whales.

Adula simpsoni has the exceptional habitat of settling in the sutures and inside the craniums of old skulls of whales, where it attaches firmly by means of the byssus threads.The bright yellow-brown shells of Adula are thin, with a glossy, varnished-like periostracum. It grows to a maximum length of 30mm, but shells approaching this size are always corroded, a factor that, given the extremely thin nature of the shells, probably brings about the death of the animal through exposure to predatory invertebrates. Growth stages on the shells are not very obvious, but it is likely that the life-span of Adula is not very long despite the otherwise protective nature of its environment.

The glossy shells of Adula grow up to 30mm long; the mollusc is found on old whale skulls.

The glossy shells of Adula grow up to 30mm long; the mollusc is found on old whale skulls.