Coronula diadema – Whale barnacle
1998.6.305 – 44mm x 52mm
This crown shaped shell is a whale barnacle. Although once thought to be related to snails, shells like this are actually crustaceans and more closely related to crabs.
Coronulid barnacles belong to the superfamily Coronuloidea, which includes species adapted to live on turtles, manatees, crabs, and snakes. This particular crustacean is a species found on humpback whales and attaches itself to areas around the lips, the long grooves of the throat and the genital region.
The barnacle begins its life as a free-swimming larva. When the larva findsa whale host, it then develops the heavy calcite plates that shield the soft body of the barnacle. As the plates grow and fuse, the whale’s skin is drawn into the spaces between the plates which helps cement the shell to the whale. You can see in the photographs that the barnacle has longitudinal ribs with strong transverse growth ridges. Even if the barnacle only lives for a few years the shell can be attached to the whale for many years after.
The barnacle does not hurt the whale; it has successfully evolved to live as a hitchhiker to get access to more food. Eventually the shell can fall off and they sometimes appear on the shores of beaches. To find one is very lucky indeed. This specimen was found on the shores of South Georgia and donated to the museum in 1998.
These barnacle shells are also found in the fossil record which gives palaeontologists information to be able to map ancient migration routes of whales by looking at the distribution in the sediments and rocks.