means a bivalve mollusk with a dark, elongated shell that clings to rocks and ropes by tough filaments, often gathered and eaten.

from From Old English 'muscle' or 'muxle,' itself from Latin 'musculus' — literally 'little mouse,' the same word that gave us 'muscle.' The Romans saw the small dark shellfish and apparently thought of a crouching mouse, so the clinging shellfish and the flexing bicep are linguistic siblings, both named for an imagined rodent.