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Valves and Rear Hinge
Like a mollusc, a brachiopod has shells (the "valves") covering its soft parts. The hard upper and lower convex shells cover its dorsal and ventral surfaces and are connected at by a hinge. The bigger shell is called the pedicle valve because it bears the pedicle, or anchoring structure. The smaller shell, known as the brachial valve, holds the lopophore, or main feeding organ.
Articulate brachiopods have a rear hinge consisting of a projection, or "tooth," in the pedicle valve that fits into sockets located on the brachial valve. Inarticulate brachiopods, on the other hand, have untoothed hinges supported by complex muscles.
Mantle
Like all shellfish, brachiopods also have a mantle --- a skin-like tissue that secretes and lines the outer shell and encases their soft internal organs. The mantle is responsible for managing the organism's slow growth in size by extending the shells' outermost "skin," also known as the periostracum , along its edges. The shells harden as the organism builds biomineralized layers under the extended skin. Many brachiopods have a mantle further equipped with bristles known as setae, which serve as extra defense and as sensory organs.
Lopophore and Body
The cavity inside the two valves is occupied mainly by the animal's lopophore, which resembles a convoluted tube with small hairlike projections known as cilia. The lopophore filters food particles from water and transports them to the mouth by means of the cilia. The rest of the brachiopod's body takes up a mere third of the space between the shells and consists mainly of the pharynx, esophagus, stomach, heart, ganglia and gonads.
Pedicle
The pedicle, a long, fleshy appendage, holds the entire organism in place. It protrudes from an opening near the hinge and is protected externally by a cuticle made of chitin. Chitin is a tough and semi-elastic tissue present in most exoskeletons of other arthropods. In some species, the pedicle is strong enough to lift the entire animal up from where it rests, while in others, it is hardly anything more than a leash. The pedicle anchors the animal onto a surface with rootlike extensions or with small bumps called papillae.