(Latin.brachio = arm + Greek.pod = foot)
Brachiopoda have a calcium carbonate shell.
They bear a superficial relationship to bivalve molusks, but they are only distantly related. The shells of lamp shells consist of two plates (valves), one ventrally beneath the body and another dorsally above it. Most are attached by a short fleshy stalk (peduncle). The shape of the shells and this little stalk earned these animals their names.
A section through a brachiopod.
Braciopods dominated the early seas when since animal life was first common, but now only a handful exist.
Characteristcs:
1. Symmetry bilateral. No segmentation. Triploblastic.
2. External is covered with a shell, dorsal and ventral valves are unlike. The shell usually has a fleshy peduncle for attachment.
3. Mouth preceded by an extensive two armed lophophore. The digestive canal exists with or without an anus.
4. The coelom is well developed and filled with fluids. The circulatory system is open. The blood is colourless and with coelomocytes.
5. Excretion takes place by one or two nephridia serving also as reproductive ducts.
6. A nerve ring about gullet.
7. The sexes are usually seperate, each with paired gonads. Eggs and sperm are discharged into the seawater around it. A free swimming ciliated larva is born. No asexual reproduction takes place.
