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Lingula - some things never change

Let the rocks tell their story

story under development...
Lingula is often considered a "living-fossil" based on its supposed lengthy morphological conservatism owing to its absence of evolution, and its remarkable survival for more than 550 M.Y. This conclusion is based on the typical apparently unchanged "linguliform" shape of the shell.
Lingula or forms very close in appearance have existed possibly since the Cambrian

fissil lingula

living lingula

Scientific explanation:
The linguliformean subphylum is regarded as the most primitive of the brachiopods.
They lack any form of shell articulation and rely on a complex internal musculature to keep the valves in place and to move them.
The pedicle in these forms appears from between the two valves rather than a dedicated foramen in one of the valves as seen in the more derived brachiopod subphyla.Also, unlike the other two brachiopod subphyla which have calcium carbonate shells, the ligulids have an organophosphatic shell.
 This hints at a primitive condition.