Hobbies And Interests
Symmetry
The top and bottom shells of a brachiopod are different in shape. Brachiopod shells are bilaterally symmetrical, with the right half of each shell a mirror image of the left. Their plane of symmetry runs vertically down the middle of each shell. Bi-valve clams exhibit a different kind of symmetry, with the plane of symmetry running along the line where the two shell halves meet. The top and bottom shells are often identical.
Feeding Systems
Both clams and brachiopods live and feed in the sediment of shallow ocean waters, often near the shore. They're filter feeders with important anatomical differences, living off tiny aquatic marine organisms and organic matter. Clams use a siphon-like structure to feed while buried in sediment. They draw water into their shells to be filtered by a set of gills. Brachiopods possess a specialized feeding filter apparatus called a lophophore. It resembles a fringe of small tentacles drawing food particles into the animal's mouth.
Mobility
Most brachiopod species anchor themselves to the ocean floor with a muscular stalk-like appendage known as a pedicle. They remain in place and don't move. Clams use an extendable foot for mobility and to bury themselves in the sediment or sand of the ocean floor. Some clams can clap their shell halves together and swim for short distances. Clams use muscles to open their shells and ligaments to close them. Brachiopods use muscle power to both open and close their shells.
Fossils
Brachiopods are so abundant in the fossil record that scientists use specific species to date rock layers. Until the Permian extinction of 250 million years ago, brachiopods were more widespread and numerous than clams. Brachiopods and clams arose during the Cambrian period and peaked in diversity and numbers during the Paleozoic era of 400 million years ago. After the Permian extinction, clams took over and occupied the ecological niches formerly inhabited by brachiopods.