Lingulata is a class of brachiopod, among the oldest of all brachiopods having existed since the Cambrian period. They are also among the most morpholically conservative of the brachiopods, having lasted from their earlier appearance to the present with very little change in shape. Shells of living specimens found today in the waters around Japan are almost identical to ancient Cambrian fossils.
The Lingulata have tongue-shaped shells with a long, fleshy stalk with which the animal burrows into sandy or muddy sediments. They inhabit vertical burrows in these soft sediments with the anterior end facing up and slightly exposed at the sediment surface. The cilia of the lophophore generate a feeding and respiratory current through the lophophore and mantle cavity. The gut is complete and J-shaped.
Lingulata shells are composed of a combination of calcium phosphate, protein, and chitin. This is unlike most other shelled marine animals, whose shells are made of calcium carbonate. The Lingulata are inarticulate brachiopods, so named for the simplicity of their hinge mechanism. This mechanism lacks teeth and is held together only by a complex musculature. Both valves are roughly symmetrical.