Reference work entry
Brachiopods are benthic invertebrates that live as single entity or in groups. They have concrete cavities, no segments and are bilaterally symmetrical. They also have two shells of unequal sizes, which are composed mainly of calcium or chitinophosphatic materials. There are approximately 100 genera and 300 species of existing brachiopods, but they flourished in the past. Approximately 3,500 genera and more than 30,000 species have already been illustrated. Brachiopod fossils are important for determining geological age. Brachiopods thrived from the Silurian to the Permian and are mainly preserved in limestone, marl and calcareous shale. Some specimens have higher ornamental value because many individual fossils tend to cluster together in the same rock. Brachiopod fossils have mainly been found in Hunan, Guangxi, Hubei, Yunnan and Guizhou Provinces (Fig. 24).
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