Brachiopod
Brachiopod
Brachiopod (pronounced: /ˈbrakiəˌpäd/), from the Greek words "βραχίων" (brachion) meaning "arm" and "πούς" (pous) meaning "foot", is a phylum of marine animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopods are among the most common fossils, with some 12,000 fossil species recognized.
Etymology
The term "Brachiopod" is derived from the Ancient Greek words "βραχίων" (brachion) meaning "arm" and "πούς" (pous) meaning "foot". This refers to the structure of the brachiopod, which features a stalk-like "foot" and arm-like structures within the shell that are used for feeding.
Anatomy
Brachiopods have two shells, known as valves, that are usually made of calcium carbonate. The valves are hinged at the rear end, and the animal opens them at the front to feed. Inside the shell, brachiopods have a lophophore, a crown of tentacles that they use to filter food particles out of the water.
Classification
Brachiopods are divided into two major groups: the inarticulate and articulate brachiopods. Inarticulate brachiopods have shells that are not hinged and are held together by muscles, while articulate brachiopods have a hinge mechanism.
Evolution
Brachiopods first appeared in the early Cambrian period and reached their greatest diversity in the Devonian and Carboniferous periods. They suffered a major decline in the Permian-Triassic extinction event, but have persisted to the present day with about 300 living species.
Related Terms
- Lophophore: A crown of tentacles that brachiopods use to filter food particles out of the water.
- Inarticulate brachiopods: A group of brachiopods with shells that are not hinged and are held together by muscles.
- Articulate brachiopods: A group of brachiopods with a hinge mechanism.
External links
- Medical encyclopedia article on Brachiopod
- Wikipedia's article - Brachiopod
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