Acorn Barnacle

Semibalanus balanoides

What do they look like?

These barnacles have rough, greyish-white shells formed of 6 shell plates. There is a kite-shaped opening at the top through which—if you look closely—you might see two pairs of tightly sealed valves when out of water. When submerged, these valves open and 6 pairs of black, jointed legs (cirri) will emerge, forming a fan.

Where can I find them in Scotland?

Acorn barnacles can be found all around the coasts of Britain and Ireland and are the most common barnacle to be found on our shores. They will colonise any hard coastal substrate, from rocks and boats to the legs of piers or even the shells of other animals.

Up to 1.5cm
Up to 8 years
Conservation Status

Fun Fact
Acorn barnacles use their legs to catch their prey! Inside their shells, the shrimp-like creature effectively stands on its head and kicks particles of food into its mouth.

When rockpooling, please be careful to leave everything as you found it.

Discover more about how to rockpool responsibly by watching our Beginner's Guide.

Barnacles of varying sizes are crammed together on a sandstone rock
© Susan Davies