Description: A large, white acorn barnacle that can reach up to 50 mm diameter. It may occasionally have a brownish tinge. The outer shell is made up of 6 plates and is broadly circular in shape with a very irregular edge. The plates are usually ridged and form a tall, steep cone. The opercular aperture is relatively small and teardrop shaped, and the operculum is deeply recessed when it is closed. The tergo-scutal flap is brown to purple in colour and edged with yellow.

Habitat: Found from shallow subtidal to depths of over 150 m.

Distribution: Found around all coasts of Britain and Ireland.

Similar Species: Could be confused with other species of Balanus or other acorn barnacles. The relatively small opercular aperture combined with the ridged plates and colour of tergo-scutal flap help to distinguish it from other species.

Key Identification Features:

• Large white acorn barnacle up to 50 mm in diameter.
• Outer shell consists of 6 ridged plates that form a tall, steep cone.
• Very irregular edge to outer shell.
• Relatively small opercular aperture.
• Tergo-scutal flap brown to purple, edged in yellow.

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

iNaturalist: Balanus balanus at iNaturalist World Species Observations database.

WoRMS: Balanus balanus at World Register of Marine Species.