The two halves of the shell are equal in size and similar in shape, being elongated and asymmetrical, with a dysodont hinge between the valves.

The outline is mytiliform with a terminal umbo, but the shape is very variable and specimens may be highly expanded posteriorly, occasionally curved; sometimes almost cylindrical with the beaks being sub-terminal.

[4] In the cooler waters of the western Mediterranean, B. pharaonis is restricted to habitats with higher temperatures and salinities, where it establishes dense mussel beds on hard substrates, especially where it is sheltered from waves.

[3] Brachidontes pharaonis was first recorded in the Mediterranean Sea in 1876 off Port Said in Egypt, reaching Lebanon and Palestine by the 1930s; Sicily by 1971; Greece by 1979; Syria and Turkey by 1985, Rhodes by 1989, Cyprus by 1996, and the northern Adriatic coast of Croatia by 1997.

[3] A species of whelk, Stramonita haemastoma, was found to preferentially prey on B. pharaonis off the coast of Israel[3] and in the south of Italy.

By the late 1990s Israeli surveys were showing that there had been a rapid shift in dominance, demonstrating that some populations of B. pharaonis had reached densities of up to 300 specimens per 100 cm2, while M. minimus was very infrequently encountered.