Brachiopods are superficially similar to bivalves, both having two shells. Brachiopods are easily distinguished from molluscs because they have (different) dorsal and ventral shells. Bivalves have mirrored right and left shells. "Lingula" and most brachiopods also have a stalk (or peduncle) that extends through a hole near the tip of one of its shells. Bivalves may be attached to a substrate with byssus filaments, that extend from between the shells.