This fossil structure shows molds and casts of a brachiopod species. Brachiopods are distinguished by their bilateral symmetry, with the line of symmetry along the shell running perpendicular to the hinge. Growth lines are indicated by the green markers. The yellow lines highlight the ribs of the brachiopod, usually these are more noticeable in better-preserved samples. Brachiopods first appeared in the rock record in the Cambrian period of the Paleozoic era and there are around 300 species still alive today. They occupy marine environments and have a wide salinity tolerance, so they can inhabit fresh and salt-water ecosystems.