Specimen collected from Penzance. Length = 9mm.
<em>Musculus costulatus</em> (Risso, 1826)
Distributed from the south Britain to the Iberian Peninsula and into the Mediterranean.
Lives amongst algae and stones disguised with fragments of shell or gravel mixed up with the byssus threads. Feeds by filtering phytoplankton.
Brittle shell up to 1.5cm in length. It is dirty white in colour marked with purple brown streaks. The inside of the shell is pearly and sometimes dark brown. The surface of the shell is sculptured with fine concentric lines and ribs in the anterior and posterior region of the shell. The margin is crenulate where there are aribs but smooth elsewhere.