Brachiopoda
English: Brachiopods; Lamp shells; Lampshells; Brachs.
Name: from Latin brachium, arm and poda, foot.
Clades: Mollusca; Spiralia; Animals.
Zoology
Molluscs; marine, benthic; valves or shells, 2, hard, on the upper and lower surfaces,hinged at the rear end, while the front can be opened for feeding or closed for protection; sessile, with a stalk-like pedicle projecting from an opening in one of the valves, the pedicle valve, attaching the animal to the seabed.
Taxonomy
Brachiopoda resemble Bivalvia to which they are not closely related.
Brachiopods have a plane of bilateral symmetry through the valves and perpendicular to the hinge. The two brachiopod valves differ in shape and size from one another.
Bivalvia usually have a plane of symmetry between the valves of the shell, which are mirror images of each other.
Brachiopods close with adductor muscles, and open iwth internal diductor muscles.
Bivalvia close their two valves with adductor muscles, and open them by means of an external or internal ligament.
Brachiopods are attached to the substrate by means of a fleshy "stalk" or pedicle.
Brachiopods are fixed to the substrate.
Bivalvia are mostly free-moving, usually by means of a muscular foot; some pelecypods such as oysters, mussels and the extinct rudists are fixed to the substrate.
Brachiopoda shells are sometimes made of either Calcium phosphate.
Bivlavia shelles are made of Calcium carbonate.
Subclasses
Articulate brachiopods have toothed hinges and simple opening and closing muscles.
Inarticulate brachiopods have untoothed hinges and a more complex system of muscles used to keep the two halves aligned.