Description: A white to grey, 6-plated acorn barnacle with overlapping lateral plates, reaching a maximum diameter of around 15 mm. Overall form of the barnacle varies from a low cone to a tall tubular shape if they are crowded. The rostral plate (bottom plate) is wider than the opercular aperture. The aperture itself is broadly diamond shaped and has a stepped or sinuous suture visible. The tergo-scutal flap is white in colour.

Habitat: Found intertidally on most shores where there are hard substrata available. Occasionally found subtidally.

Distribution: Widespread around Britain and Ireland.

Similar Species: Could potentially be confused with other acorn barnacles but the overlapping lateral plates and the rostral plate being wider than the aperture are good diagnostic features.

Key Identification Features:

• 6-plated white acorn barnacle.
• Overlapping lateral plates.
• Broadly diamond-shaped operculum.
• Rostral plate wider than aperture.
• Stepped or sinuous suture visible across opening.

Distribution Map from NBN: Semibalanus balanoides at National Biodiversity Network mapping facility, data for UK.

iNaturalist: Semibalanus balanoides at iNaturalist World Species Observations database.

GBIF data for Semibalanus balanoides

WoRMS: Semibalanus balanoides at World Register of Marine Species. Accepted name: Semibalanus balanoides (Linnaeus, 1767). AphiaID: 106210.

Classification: Biota; Animalia; Arthropoda; Crustacea; Multicrustacea; Thecostraca; Cirripedia; Thoracica; Thoracicalcarea; Balanomorpha; Balanoidea; Balanidae; Semibalaninae; Semibalanus