What they are
Lingulides, Brachiopods
Morphology
In many ways, Brachiopods resemble Pelecypods. Brachiopods have two shells, called valves, which house the creature inside. Through a hole in one of the valves, known as the pedicle foramen, extends a fleshy ligament called the pedicle. The pedicle is used by the brachiopod to attach itself to the sea floor.
The key difference between brachiopods and pelecypods is in their respective symmetries. Pelecypods have a line of symmetry along their hinge line. This means that the top and bottom shells of the animal are mirror images of one another. Brachiopods, however, have their line of symmetry normal, or perpendicular, to their hinge line. This means that the left side of both the top and bottom valves are a mirror image of the right side of both the top and bottom valve.
Ecology
Brachiopods live exclusively on the sea floor; they are therefore called Benthic animals. Most brachiopods live on the shallow continental shelf. However, there are a few species that can live in depths exceeding 5000m.
Most brachiopods tolerate only normal marine salinity, but a few species, such as the ligulides, can live in brackish salinities.
Brachiopods cannot burrow into the sea floor, consequently remaining near the surface of the sea floor. Here, currents can bring fresh food and oxygen to the creature while removing waste products.
All brachiopods are filter feeders and are incapable of moving in search of food. Brachiopods use what is called a lophophore, a fan-like filter-feeding device, to gather food from the surrounding water. The brachiopod will open its valves slightly and allow water to enter. The creature then shuts its valves and whips its lophophore around the water inside, gathering food particles. The creature then opens up to flush out the old water and allow new water to enter.