Inarticulata

The Inarticulata are a class of brachiopods, which are marine invertebrates. Unlike other brachiopods, their shells are unhinged and typically made of chitinophosphatic material, lacking teeth and sockets. These ancient creatures, commonly known as lamp shells, have a history stretching back to the Cambrian Period. While once abundant, modern brachiopods are less diverse, but the Inarticulata order still includes forms like Lingula. They are distinguished by their simple shell structure and the way their pedicle, a stalk-like organ, develops.12