Brachiopoda (phylum)

Bottom-dwelling marine invertebrates characterized by being covered by two valves or shells, with one valve covering the dorsal or topside and the other covering the ventral or bottom side. They are so named for the Greek words meaning "arm" and "foot," and are commonly known as lamp shells because they resemble early Roman oil lamps. Although some evolutionary development is traceable from their appearance in the Cambrian Period to the present, it is still not completely understood.