Horse mussels (Modiolus)
are true Jurassic survivors. You can still find their shells
on the beach today.
They lived by clinging to rocks.
In life, there would have been two half-shells joined by a hinge.
Modiolus could lock itself away by keeping the hinge firmly
closed, thanks to a strong set of interlocking teeth.
The picture shows a Modiolus
found in a brick pit at Napton.