Lingulata

Lore & Background

Lingulata have tongue-shaped shells, hence the name from the Latin word for 'tongue,' with a long fleshy stalk called a pedicle used to burrow into sandy or muddy sediments. They inhabit vertical burrows 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, and the gut is complete and J-shaped.

Reader's Guide

Lingulata are significant as one of the oldest brachiopod classes, with a fossil record extending back to the Cambrian period. Their extreme morphological conservatism—living specimens nearly identical to Cambrian fossils—makes them a key subject for studying evolutionary stasis. Unlike most shelled marine animals, their shells are composed of calcium phosphate, protein, and chitin, not calcium carbonate. As inarticulate brachiopods, their hinge mechanism lacks teeth and is held together only by complex musculature, with both valves roughly symmetrical. The genus Lingula, primarily Indo-Pacific, may be the oldest known animal genus still containing extant species and is harvested for human consumption in Japan and Australia. However, some researchers argue that the genus Lingula is not as old as commonly thought, introducing uncertainty into its status as a 'living fossil.'

Did You Know?

• Their shells are composed of calcium phosphate, protein, and chitin, unlike most shelled marine animals.
• The genus Lingula may be the oldest known animal genus that still contains extant species.
• Living Lingulata specimens found in waters around Japan are almost identical to ancient Cambrian fossils.