Brachiopoda (arm foot)

Brachiopods get their name from internal paired appendages, the brachidia, which filter
water and pass food into the mouth. The body of the animal is covered by a mantle, a soft tissue layer which lines the two shells. These shells enclose and protect the animal. Brachiopods have a well-developed digestive system, but most lack an anus. They have a mouth, stomach, intestine, and a blood vascular system with a heart-like sac. Two nerve centers pass around the gullet. Reproduction is carried on by male and female brachiopods.

Brachiopods have two bilaterally symmetrical valves that are similar in shape but unequal in size. If the shells are hinged, the animals are called articulate brachiopods; if hingeless, they are called inarticulate brachiopods. A pedicle, or fleshy stalk, is attached to the interior of the larger valve by muscles. This pedicle secures the animal to the sea floor. Brachiopods are not colonial, but live in clusters in marine water. They appeared in the Early Cambrian (ca. 525 million years ago) and continue into the preseent. Because they are represented by numerous species that lived for specific lengths of time, they are excellent markers for the correlation of strata.

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