Biodiversity & Conservation

An acorn barnacle - Semibalanus balanoides

Semibalanus balanoides

Image Keith Hiscock - Group of individuals. Image width ca XX cm.
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Distribution map

Semibalanus balanoides recorded (dark blue bullet) and expected (light blue bullet) distribution in Britain and Ireland (see below)

Why do the maps differ?

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Semibalanus balanoides is not listed under any importance categories.

Taxonomy icon Taxonomy Taxon English term
Phylum Arthropoda Arthropods, joint-legged animals, e.g. insects, crustaceans & spiders
Class Maxillopoda Barnacles, copepods and fish lice
Authority Linnaeus, 1767
Recent synonyms Balanus balanoides
Map icon Recorded Distribution in Britain and Ireland All coasts of Britain & Ireland, but sometimes is absent or rare in south-west Cornwall, the Isles of Scilly and south west Ireland.
Habitat information icon Habitat information Semibalanus balanoides is a dominant member of the eulittoral fauna of British rocky shores. It can be found on shores of all exposure and typically occurs in a zone below Chthamalus montagui, although the two can overlap. It may extend into the lower reaches of estuaries as it can tolerate salinities down to 20 psu.
Text page icon Description Semibalanus balanoides is the most widespread intertidal barnacle in the British Isles. It may grow up to 15 mm in diameter and has 6 calcified grey-white shell plates. It may be distinguished from other barnacles by the presence of a diamond shaped opercular aperture and a membranous shell base. The barnacle feeds on zooplankton when immersed, by extending the thoracic appendages (cirri). It is a cross fertilizing hermaphrodite and may live for up to 8 years, depending on its position on the shore.
Identifying features
  • Shell wall of 6, grey-white plates.
  • Opercular aperture diamond shaped.
  • Rostral plate broad.
  • Up to 15 mm in diameter.
  • Shell base membranous.
  • Tissue inside opercular aperture usually white or pinkish-white.
Additional information icon Additional information No text entered

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This review can be cited as follows:

Nicola White 2008. Semibalanus balanoides. An acorn barnacle. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 03/09/2010]. Available from: <http://www.marlin.ac.uk/speciesinformation.php?speciesID=4328>