Lingula

Lingula is a genus of brachiopods in the class Lingulata. "Lingula" is known to have existed since the early Ordovician period. "Lingula" is a good example of a living fossil. Like all brachiopods, it is a filter feeder.
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.
The Lingulata brachiopods have existed from the Cambrian period to the present, a time span of over 500 million years! Modern species of "Lingula" are very similar from their fossil ancestors.