Elminius modestus

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Elminius modestus

Elminius modesutus and Semibalanus balanoides

Kingdom:	Animalia
Phylum:	Arthropoda
Subphylum:	Crustacea
Class:	Maxillopoda
Order:	Sessilia
Family:	Balanidae
Genus:	Elminius
Species:	E. modestus

Binomial name

Elminius modestus
Darwin, 1854

Elminius modestus is a barnacle of the family Balanidae, native to Australia and especially New Zealand. It is found intertidally on solid surfaces around southern Australia and New Zealand, often forming dense mats, except where there is intense wave activity.

Elminius modestus is a small barnacle, protected by four calcified shell plates, attached to a wide range of substrates - rocks, metal, wharf pilings, and mollusc shells. Its general shape is low and conical with a diamond-shaped opercular aperture. In young barnacles the shell plates have a star-shaped base - older specimens have marked vertical ridges that give the barnacle an irregular, roughly circular margin.

Elminius modestus has become an invasive species in Britain and Europe. It was first described at Chichester Harbour in 1946, and is thought to have been transported in the ballast water of ships during World War II. It rapidly spread throughout Britain and northern Europe, being found on almost all shores of Britain by the 1970s. Elminius modestus not only competes with native British species, particularly Semibalanus balanoides, but has colonized some sheltered and estuarine habitats not previously inhabited by them. However, E. modestus is not able to colonise high wave action areas and these remain relatively safe for endemic barnacle species.

Coloration is opalescent greyish-white in juveniles and spat (newly settled and metamorphosised larvae) while adults are a drab grey colour.

Maximum size is about 10 mm in diameter.