Brachiopods are marine invertebrate animals with two shells. Although they outwardly resemble clams (which are bivalve mollusks), they are not closely related and their internal anatomy is completely different. During the Paleozoic era (542-250 million years ago), brachiopods were one of the most abundant and diverse groups of marine organisms. This changed after the mass extinction at the end of the Paleozoic, and since then the abundance and diversity of brachiopods have been low relative to clams and most other major groups of marine invertebrates. In modern oceans, brachiopods tend to live in sheltered or hidden habitats with few predators and low food levels. Some scientists have suggested that these habitats are similar to those dominated by brachiopods in the Paleozoic.
Several groups of living brachiopods have shells that are very similar to those found as fossils in Paleozoic rocks, including the inarticulate brachiopods shown below.
Recent specimen of the brachiopod Lingula anatina from the Phillipines (PRI 76882). Specimen is from the collections of the Paleontological Research Institution, Ithaca, New York. Longest dimension of specimen is approximately 6 cm.
Fossil inarticulate brachiopod Lingula punctata from the Devonian Ludlowville Fm. of Seneca County, New York (PRI 76824). Specimen is from the research collections of the Paleontological Research Institution, Ithaca, New York. Maximum dimension of specimen is approximately 11.5 cm.