Description: This bivalve reaches around 5 cm and has a swollen, solid shell with a very irregular outline and shape. The outline is broadly trapezoidal, and t is described by Tebble as being 'generally boat-like in shape with its wide cardinal area suggesting the flight deck of an aircraft carrier.' There is a wide byssal gape. It is dirty white to pale yellow or brown, with a light to dark brown periostracum. The outside of the shell is often heavily encrusted with calcareous algae or worm tubes, and may be worn in places especially if situated in a rock crevice. It has a straight hinge plate with 40-50 teeth. Shell interior is white with brown margins, sometimes with pale green or purple blotches.

Habitat: Found from lower shore to almost 100 m, attached via a large green byssus inside dead shells, small rocks or in crevices.

Distribution: Found on all coasts of Britain and Ireland aside from the SE coast of England.

Similar Species: Unlikely to be confused with any other species.

Key Identification Features:

• Distinctive swollen shape.
• Large green byssus.
• Prominent byssal gape.
• Straight hinge plate with 40-50 teeth.
• Shell interior white with brown margins, and green or purple blotches.

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

iNaturalist: Tetrarca tetragona at iNaturalist World Species Observations database.

GBIF data for Tetrarca tetragona

WoRMS: Tetrarca tetragona at World Register of Marine Species. Accepted name: Tetrarca tetragona (Poli, 1795). AphiaID: 751302.

Classification: Biota; Animalia; Mollusca; Bivalvia; Autobranchia; Pteriomorphia; Arcida; Arcoidea; Arcidae; Tetrarca