Geological History
Modern clam shrimp have no significance to humans. However, extinct species of these crustaceans are often studied by geologists. In freshwater deposits, generally poor in fossils, the well-preserved clam shrimp shells are found quite often. They help identify the age of the corresponding strata.
During the past geological periods clam shrimp were apparently more numerous and common than they are now. 300 extinct species are known, and half as many living species. The oldest clam shrimp, such as Asmussia murchisoniana, were found in Devonian deposits. Many extinct species, especially Triassic ones, lived in the sea, where no clam shrimp remain today.
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