Species description: Shells usually range in length from 20 mm to around 50 mm (rarely up to 60 mm) and have a distinctive oval shape, with a white to cream coloration and mottling or blotches of orange to brown-red. They can sometimes be relatively flat, but some shells have a very domed appearance. They are smooth in texture aside from irregularly spaced growth lines. The shell tapers to a point but this is off to one side, and gives some shells a ‘hooked’ appearance. Commonly known as the slipper limpet due to the appearance of the shell when turned upside down - there is a white plate projecting from the tapered front end to about half the length of the shell, giving appearance of a slipper.

Habitat: Found from the lower shore to shallow sublittoral, although has been reported from depths of up to 60 m. Usually attached to rocks or shells. Often associated with the blue mussel Mytilus edulis and the native oyster Ostrea edulis but have been found growing on a range of other animals that provide a suitable hard substratum to which they can attach.

Ecology: These shells form chains or stacks of up to 12 individuals growing on top of one another. The large shells at the bottom are female, and the smaller shells on top are males, while the intermediate shells are intersex.

Distribution: Throughout the island of Ireland it has mainly been recorded in Belfast Lough, with a few records from other areas including Lough Foyle and Carlingford Lough. Widespread around coasts of southern Britain with a few records from east Scotland. Any new sightings should be reported.

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

Key Identification Features:

• Very distinctive oval shell with ‘slipper’ appearance on underside.
• White-cream coloration with blotches or streaks of orange – brown-red.
• Can form chains of shells.
• Attaches to a range of hard substrata, but most commonly associated with oysters and blue mussels.

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

iNaturalist: Crepidula fornicata at iNaturalist World Species Observations database.

WoRMS: Crepidula fornicata at World Register of Marine Species. Accepted name: Crepidula fornicata (Linnaeus, 1758). AphiaID: 138963.

Classification: Biota; Animalia; Mollusca; Gastropoda; Caenogastropoda; Littorinimorpha; Calyptraeoidea; Calyptraeidae; Crepidula