Acorn Barnacle - Semibalanus balanoides

Characteristics:

The two cover plates can be closed entirely to preserve the humidity inside while waiting to be flooded by waves or tidal water. Sometimes the barnacle sits on places where it can only be reached by extremely high tide. The carapace is build from 6 calcified shell plates. The diameter sometimes reaches 15 mm, the height usually a little less.

Habitat:

It is most frequent from the high tidal to the subtidal zone, often of very exposed locations. It tolerates low salinity very well.

Distribution:

This is one of the most widespread barnacles on the northern hemisphere. Along the Norwegian coast it can be found as far north as the western parts of Finnmark.