Brittle shell up to 1.5cm in length. The shell is yellow brown in colour but this is obscured by thick green or brown periositracum. The inside is generally white but sometimes pale purple. The surface of the shell is sculptured with fine concentric lines and radiating ribs. Margin of the shell is crenulate.
- Anterior region of shell has 8-12 ribs; posterior 30-40 ribs
- Periostracum is pale green of brown
Found under rocks and among algae. Spins together algae to create a nest from where it filters phytoplankton
CommonNorway south to the Mediterranean