Clam shrimp are a group of branchiopod crustaceans that possess bivalved carapaces, which resemble the shells of unrelated bivalved molluscs. Clam shrimp are now divided into three orders, Cyclestherida, Laevicaudata, and Spinicaudata, in addition to the fossil family Leaiidae. Clam shrimp nauplii are distinguished by very small front antennae. At the second stage (metanauplius), the larva develops the small shell. They develop very quickly. For instance, Cyzicus reaches sexual maturity in 19 days after hatching.

Taxonomy

Extant clam shrimp belong to three orders, divided into five families; some notable genera and prehistoric taxa are also listed:<!-- genus list is very incomplete but no complete list sems to exist online -->

Spinicaudata <small>Linder, 1945</small>

  • Cyzicidae <small>Stebbing, 1910</small>
  • Caenestheria
  • Caenestheriella
  • Cyzicus
  • Eocyzicus
  • Eosestheriidae <small>Zhang & Chen, 1976</small> (fossil)
  • Bairdestheria
  • Menucoestheria <small>Gallego & Covacevich, 1998</small>
  • Euestheridae <small>Defretin, 1965</small> (fossil)
  • Laxitextella <small>Kozur, 1982</small>
  • Leptestheriidae <small>Daday, 1923</small>
  • Eoleptestheria
  • Leptestheria
  • Leptestheriella
  • Maghrebestheria
  • Sewellestheria
  • Limnadiidae <small>Baird, 1849</small> (including Imnadiidae)
  • Afrolimnadia
  • Calalimnadia
  • Eulimnadia
  • Imnadia
  • Limnadia
  • Limnadiopsis
  • Limnadiopsidum
  • Metalimnadia
  • Palaeolimnadiidae <small>Tasch, 1956</small> (fossil)
  • Krasiestheria <small>Olempska, 2004</small> (tentatively placed here)

Cyclestherida <small>Sars, 1899</small>

  • Cyclestheriidae <small>Sars, 1899</small>
  • Cyclestheria
  • Paracyclestheria

Laevicaudata <small>Linder, 1945</small>

  • Lynceidae <small>Baird, 1845</small>
  • Leptestheriella
  • Limnetis
  • Lynceiopsis
  • Lynceus
  • Paralimnetis

Fossil record

Modern clam shrimp have little 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, a practice known as biostratigraphy.

During the past geological periods clam shrimp were apparently more numerous and diverse than they are now. 300 extinct species are known, twice that of living species. The oldest clam shrimp, such as Asmussia murchisoniana, were found in Devonian deposits. Many extinct species, mostly Triassic specimens, once lived in marine environments, where no extant clam shrimp inhabit today.

See also

  • Isoxys

References

  • [http://www.sacsplash.org/critter/clam-shrimp]
  • Introduction to the Branchiopoda