Description: The shell of this piddock is a thin, brittle elongate oval. It reaches just over 6 cm in length and is an off-white to fawn colour, although it may be covered in part by a dark brown periostracum. The outer surface of the shell has at least 40 radiating ribs which become increasingly prominent towards the anterior end of the shell. The most thick and coarse of the ribs also have prominent flattened spines. The right valve has 2 cardinal teeth, the posterior of which is bifid. The left valve has 3 cardinal teeth, of which the middle is bifid. There are no lateral teeth on either valve. The inside of the shell is white and the structure of the coarser ribs is visible on the interior.

Habitat: Bores into mud, clay, peat-moss or limestone from mid to low water down to around 10 m.

Distribution: Non-native to this area but now established in Britain, mostly in southern half with some records from northern isles. No records so far from the island of Ireland.

Similar Species: Quite distinctive but could potentially be confused with Pholas dactylus.

Key Identification Features:

• Thin and brittle shell in the shape of elongate oval.
• At least 40 radiating ribs.
• Ribs towards anterior becoming more coarse and featuring prominent flattened spines.

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

iNaturalist: Petricolaria pholadiformis at iNaturalist World Species Observations database.

GBIF data for Petricolaria pholadiformis

WoRMS: Petricolaria pholadiformis at World Register of Marine Species. Accepted name: Petricolaria pholadiformis (Lamarck, 1818). AphiaID: 156961.

Classification: Biota; Animalia; Mollusca; Bivalvia; Autobranchia; Heteroconchia; Euheterodonta; Imparidentia; Venerida; Veneroidea; Veneridae; Petricolinae; Petricolaria