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Adult S. balanoides grow up to 15 millimetres (0.6 in) in diameter, and are sessile, living attached to rocks and other solid substrates. When the tide rises to cover the barnacles, the operculum opens, and feathery cirri (modified thoracic appendages) are extended into the water to filter food from the seawater.
Widespread boreo-arctic species. These were seen in beaches of Unst, Shetland I.