This Permian brachiopod fossil is from Western Australia and is 250-300 million years old. Brachiopods are commonly known as lamp shells and are marine invertebrates (unlike bivalves which are marine or aquatic).
The oldest known fossils are Cambrian 460-510MYA and the largest known fossil brachiopods were 30-38cm from Carboniferous.
Brachiopod fossil species diversity have been useful indicators of climate change.
Shells of brachiopods are attached to the dorsal and ventral surfaces of the organism, compared to bivalves which are attached laterally. Read more about the internal and external features of brachiopods here.
One specimen only included (two halves best match).