Petricolaria pholadiformis (Lamarck, 1818)Veneroidea : Petricolidae
To size: To 64mm. Shell Structure: Thin, fragile shell. Equivalve: Equivalve. Equilateral: Inequilateral. Beaks in front of midline. Tumidity: Not tumid. Outline: Elongate oval. Lunule not well-developed. Radiating ridges distinguish it from rest of shell. Escutcheon absent.
Sculpture: Radial ribs which, in the anterior, are developed into rib-like lamellae at the concentric lines. Margin: Smooth. Ligament: Inset, but highly visible, chesnut brown in colour. Runs almost to the end of the dorsal margin. Hinge: 3 cardinals in LV, the central is bifid and hooks from under the umbo, not on hinge plate. 2 cardinals in RV, posterior is bifid, the anterior originates beneath umbo and is hook-like. Pallial Musculature: Pallial sinus deep, extending past the midline. Periostracum: Thin, matt. Colour: White/cream.
Distribution & Ecology
Petricola pholadiformis was introduced not later than 1890 (Naylor 1957) and found in the River Crouch, Essex International Council for the Exploration of the Sea; 1972, Tebble 1976).
The species is native to the USA and was introduced from there. It is established along south and east coasts of England from Lyme Regis, Dorset, to the Humber, Humberside (Duval 1963; J. Light & I. Killeen pers. comm.), where it is found living in clay, peat or soft rock shores. It is most common off Essex and the Thames estuary e.g. the River Medway (see Bamber 1985). European populations occur from southern Norway to the Mediterranean and Black Seas (Tebble 1976).
Atlas shows records from other locations outside range shown on map. but IJK does not think that these are established. Bores into hard clay, chalk, stiff mud, peat-moss or limestone.
Juveniles & Similar Species
Key Features & Similar Species
Listed are literature citing Petricolaria pholadiformis (Lamarck, 1818). Reference containing the species Type Description is highlighted.
Lamarck J B P A de M 1818. Histoire naturelle des Animaux sans vertèbres 5. Paris. 612pp.
Purchon, R D 1955. The functional morphology of the rock-boring lamellibranch Petricola pholadiformis Lamarck. 34: 257-278.
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