Species description: A 6-plated barnacle up to 15 mm in diameter, usually wider than it is tall, giving it a low cone-like shape. The outer shell is white to cream in colour, although can often be dirty, with a rostral plate that is wider than the opercular aperture and overlaps the lateral plates. The opercular aperture is either a narrow diamond or pentagon shape with a toothed rim. There are growth lines visible on the scuta. The suture on the tergo-scutal flap usually forms an arrow point, but can be sinuous. The flap itself is white with 5 dark bands.

Habitat: Usually intertidal, but sometimes found subtidally. Can tolerate reduced salinity so can be found in estuarine and brackish areas. Found on a range of hard substrata including manmade structures.

Distribution: Scattered records from around Britain and Ireland with most concentrated in southern areas.

Similar Species: Could be confused with other 6-plated barnacles that also have diamond-shaped openings such as Semibalanus balanoides and Balanus crenatus, but the brackish habitat coupled with the 5 dark bands on the tergo-scutal flap should help distinguish this species.

Key Identification Features:

• 6-plated barnacle with a low, cone-like shape.
• Usually white to cream but can be dirty.
• Often found in estuarine or brackish environments.
• 5 dark bands on tergo-scutal flap.

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

iNaturalist: Amphibalanus improvisus at iNaturalist World Species Observations database.

WoRMS: Amphibalanus improvisus at World Register of Marine Species. Accepted name: Amphibalanus improvisus (Darwin, 1854). AphiaID: 421139.

Classification: Biota; Animalia; Arthropoda; Crustacea; Multicrustacea; Thecostraca; Cirripedia; Thoracica; Thoracicalcarea; Balanomorpha; Balanoidea; Balanidae; Amphibalaninae; Amphibalanus