Barnacles (Balanidae)

The species group can often be identified without enlarging aids
  • Bay barnacle, side view
  • A barnacle┬┤s bottom basal plate
  • Barnacles from above

Barnacles are small crustaceans that live attached to rocks and other hard surfaces in the sea. The body, which is round and 1-3 cm in diameter, is surrounded by limestone slabs. Barnacles likes to sit on other animals such as crabs, snails and mussels. Or on boat hulls. Barnacles attached to boats is a big problem because they cause increased water resistance, which means that the speed will be lower or that the boat requires more fuel. Barnacle has so-called internal fertilization, which means that with the help of a penis, sperm is transferred from one individual to the next. When the eggs hatch into larvae, they live as plankton. After a number of transformations a definitive larval form is formed, whose main task is to find a solid surface and then it will be converted into an adult barnacle, which is surrounded by  a hard calcium shell that can be opened and closed. Barnacle shells are sharp! In Nordic waters there are some 15 species and several are common along the Swedish coast.
Curiosities: The barnacle may be the animal with the longest penis in relation to their body size.

Bay barnacle (Balanus improvisus)