Semibalanus balanoides, one of the most common species on our shores. Barnacles are incredibly important creatures from an ecological perspective and are one of the true stalwarts of the coastal zone. Their abundance and distribution can help highlight long-term climatic conditions, oceanic food supply and local wave patterns. There are over 1,000 species of barnacle world-wide, but fortunately for the amateur rock-pooler there are only four species in the UK to contend with. Semibalanus balanoides can be identified most easily by a diamond-shaped opening which it uses to feed. One of three other species is an invasive non-native species (Elminius modestus or acorn barnacle) which can outcompete native barnacles in some situations. There is some excellent literature on the usefulness of barnacles as an ecological indicator.
For more information about this barnacle species, see:
Latin name: Semibalanus balanoides
Diet: The barnacle feeds on zooplankton when immersed, by extending the feathery thoracic appendages or cirri to beat passing food into the shell.
Size: up to 15mm in diameter. Their calcite shells are impermeable and help to protect against water loss when exposed to regular periods of direct sunshine.
Habitat: can be found on rocks in the inter-tidal zone around the entire coastline of Britain and Ireland
Life cycle: a cross fertilizing hermaphrodite which famously has one of the longest penises relative to body size. It may live for up to 8 years, depending on its position on the shore.