Brachiopod fossils. Brachiopods are marine invertebrates inhabiting a bivalve shell, similar to today's marine molluscs. They were common between 590 and 65 million years ago, but only a few species survive today. These three are: (right to left): Dielasma hastata, Martinia glabra and Pleuropugnoides pleurodon. All date from the Carboniferous, and were found near Castleton, England. They are part of the collections held at the Natural History Museum, London, UK.