Habitat: it lives, fixed to rocks by its long byssus, up to a few metres depth, on open rocky coasts at high hydrodynamics. Distribution: common all over the Mediterranean where in several localities it is breeded industrially for edible purposes. Plenty of it in the Black Sea too. It is diffused in many parts of the world, in temperate waters, mainly in dock habitats, employing ballast waters and ship hulls as transport vehicle. In some places this species is considered invasive, moving autochthonous species and becoming dominant species. This is due to its higher growing up and reproduction speed, notwithstanding to a better tolerance and resistance to air exposure. This species is widely cultivated in Japan and China too.
Notes: it is one of the most common species of the Mediterranean. Very changeable in form and sizes so to have a lot of synonyms and several varieties in form and colour pattern. Shell subquadrangular stretched in outline, terminal anterior umbo sharp and a little bit bent, posterior margin more or less roundish. Dorsal margin more or less sharp-cornered, ventral margin either straight or not much concave, byssal crack narrow and stretched. Surface with thin growth striae. It is present a thin but adherent periostracum. Hinge without real teeth but with crenulations changeable in number. Juvenile specimens brown in colour and more roundish in outline. Morphological differences with M edulis are mainly due to umbo bent making ventral margin concave, to valves higher and sharp-cornered on dorsal margin, to smaller sizes and to external colour darker generally.
Typical external colour uniform black violaceous, inside white pearly and margins bluish, but there were described many varieties in colour, among which we quote: radiatus Philippi and flavus Poli. having either bands brown, filiform too, or a yellowish ground with stains brown in colour.
The adult specimens average measures are around 70-80 mm in width, but form and measures can change in different areas.