Description: This small oval bivalve reaches up to 20 mm in length and has a very swollen appearance. It is an off-white to yellow-brown and may be partially covered by the light brown periostracum. There are occasionally darker sections of periostracum present and these are scattered across the surface. There are 15-18 wide ribs towards the front of the shell and 20-35 finer ribs towards the back. Inside of the shell is pearly white with external sculpturing visible.

Habitat: Found from the lower shore to shallow sublittoral. Often in algal holdfasts or on underside of shells and stones. Often found in tests of large ascidians like Ascidia mentula or Ascdiella aspersa.

Distribution: Recorded all around Britain and Ireland.

Similar Species: Could be confused with Modiolula phaseolina, Musculus niger or Musculus discors. Could potentially be confused with juvenile Modiolus adriaticus, Modiolus modiolus, Modiolus barbatus or Mytilus edulis.

Key Identification Features:

• Small oval bivalve with a swollen appearance.
• 15-18 wide anterior ribs.
• 20-35 finer posterior ribs.

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

iNaturalist: Musculus subpictus at iNaturalist World Species Observations database.

GBIF data for Musculus subpictus

WoRMS: Musculus subpictus at World Register of Marine Species. Accepted name: Musculus subpictus (Cantraine, 1835). AphiaID: 506128.

Classification: Biota; Animalia; Mollusca; Bivalvia; Autobranchia; Pteriomorphia; Mytilida; Mytiloidea; Mytilidae; Crenellinae; Musculus