Species description: A relatively small, white, acorn barnacle that reaches up to 10 mm in diameter. The outer shell is smooth and neat when young but gains vertical ridges with age that can make the outline irregular. It is broadly oval-shaped, and made up of four plates, with a diamond-shaped opercular opening. There are dark wedges on the larger pair of scutal plates. The tergo-scutal flap may be visible which is coloured white with a central orange marking.

Habitat: Grows on almost any hard surface from rocks, shells, other crustaceans to artificial structures in marinas and even on ships. Often found intertidally and can tolerate reduced salinity.

Distribution: Now widespread around Britain and Ireland, rarer on NE coast of Scotland.

Similar Species: This is the only barnacle that only has four plates which should help distinguish it from other species of white acorn barnacle which have six.

Key Identification Features:

• Small white acorn barnacle up to 10 mm.
• Four plates.
• Diamond-shaped opercular opening.
• Dark wedges on larger pair of scutal plates.

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

iNaturalist: Austrominius modestus at iNaturalist World Species Observations database.

WoRMS: Austrominius modestus at World Register of Marine Species. Accepted name: Austrominius modestus (Darwin, 1854). AphiaID: 712167.

Classification: Biota; Animalia; Arthropoda; Crustacea; Multicrustacea; Thecostraca; Cirripedia; Thoracica; Thoracicalcarea; Balanomorpha; Elminioidea; Elminiidae; Austrominius