Crabs that look like shells
Together with other barnacles and root crabs, goose barnacles form the pedunculate (barnacle) order. Their special characteristic is their sedentary life. Once the barnacle larvae have opted for a location, the Goose barnacles stay bound to this chosen location for their entire life – as shown here in the picture on a rope found off the coast of Portugal. To do so the so-called Cypris-larva anchor themselves with their backs to a firm surface, such as stone, boulders or driftwood. Later, it forms a seashell-like calcareous shell crown on a stem. Between these shells delicate spring legs filter plankton out of the water.
One more thing in common with other barnacles is the gender dualism. Self-fertilisation is only rarely necessary for a special reason: with a length which can reach eight times of the body, its record-breaking penis can effortlessly fertilise the neighbourhood.
A distinctive feature of Goose barnacle is a long, muscular stem, which can be extended to a length between 4 and 80 centimetres. This, in turn, gives the crustacean a certain mobility, since they live preferably in surf zones. Depending on the type, the striking calcareous plates are round or shaped like a scalpel. The similarity of the crustacean to a goose or duck neck gave the animals its strange name. Earlier – before knowledge of bird migration – it was even assumed that adult barnacle geese developed from the long body shape.