Leptostraca (from the Greek words for thin and shell) is an order of small, marine crustaceans. Its members, including the well-studied Nebalia, occur throughout the world's oceans and are usually considered to be filter-feeders. It is the only extant order in the subclass Phyllocarida. They are believed to represent the most primitive members of their class, the Malacostraca, and first appear in the fossil record during the Cambrian period.
Description Leptostracans are usually small, typically long, but the largest species (Nebaliopsis typica) can reach 4 cm, and the Silurian Ceratiocaris could grow to 75 cm.Invertebrate Palaeontology and Evolution They are distinguished from all other members of their class in having seven abdominal segments, instead of six. Their head has stalked compound eyes, two pairs of antennae (one biramous, one uniramous), and a pair of mandibles but no maxillipeds. They are the only malacostracans with a carapace that comprises two valves. It covers the head and the thorax, including most of the thoracic appendages, and serves as a brood pouch for the developing embryos. Its anterior tip bears a movable rostrum. Also unique among malacostracans is their eight pairs of thoracic appendages which have been specialized into leaf-like filter feeding organs, and are not used for locomotion. The first six abdominal segments bear pleopods, while the seventh bears a pair of caudal furcae, which may be homologous to uropods of other crustaceans.A phylogeny of the Leptostraca (Crustacea) with keys to families and generaMulticellular Animals: Volume II: The Phylogenetic System of the Metazoa
Leptostracans have gills on their thoracic limbs, but also breathe through a respiratory membrane on the inside of the carapace. The eggs hatch as a postlarval, or "manca" stage, which lacks a fully developed carapace, but otherwise resembles the adult.
Classification It is now accepted that leptostracans belong to the Malacostraca, and the sister crown group to Leptostraca is Eumalacostraca.
The order Leptostraca is divided into three families, with ten genera containing a total of around 40 validly described extant species:
Species Authority Date Family Distribution Nebaliopsis typica Sars 1887 Nebaliopsididae Southern Hemisphere Pseudonebaliopsis atlantica Petryachov 1996 Nebaliopsididae North Atlantic Nebalia antarctica Dahl 1990 Nebaliidae Antarctica Nebalia bipes Fabricius 1780 Nebaliidae Arctic and sub-Arctic Nebalia borealis Dahl 1985 Nebaliidae north-east Atlantic Ocean Nebalia brucei Olesen 1999 Nebaliidae Tanzania Nebalia cannoni Dahl 1990 Nebaliidae South Georgia Nebalia capensis Barnard 1914 Nebaliidae South Africa Nebalia clausi Dahl 1985 Nebaliidae Italy Nebalia dahli Kazmi & Tirmizi 1989 Nebaliidae Pakistan Nebalia daytoni Vetter 1996 Nebaliidae California Nebalia falklandensis Dahl 1990 Nebaliidae Falkland Islands Nebalia geoffroyi Milne-Edwards 1828 Nebaliidae north-east Atlantic Ocean Nebalia gerkenae Haney & Martin 2000 Nebaliidae California Nebalia herbstii Leach 1814 Nebaliidae north-east Atlantic Ocean Nebalia hessleri Martin et al. 1996 Nebaliidae California Nebalia ilheoensis Kensley 1976 Nebaliidae south-western Africa Nebalia kensleyi Haney & Martin 2005 Nebaliidae California Nebalia kocatasi Kocak, Moreira & Katagan 2007 Nebaliidae Mediterranean Sea Nebalia koreana Song, Moreira & Min 2012 Nebaliidae South Korea Nebalia lagartensis Escobar & Villalobos-Hiriart 1995 Nebaliidae Mexico Nebalia longicornis Thomson 1879 Nebaliidae South Pacific, South Africa, Caribbean Sea Nebalia marerubi Wägele 1983 Nebaliidae Red Sea Nebalia patagonica Dahl 1990 Nebaliidae Magellan region Nebalia schizophthalma Haney, Hessler & Martin 2001 Nebaliidae western Atlantic Ocean Nebalia strausi Risso 1826 Nebaliidae north-east Atlantic Ocean, Mediterranean Sea Nebalia troncosoi Moreira, Cacabelos & Dominguez 2003 Nebaliidae Spain Nebaliella antarctica Thiele 1904 Nebaliidae Kerguelen, New Zealand Nebaliella brevicarinata Kikuchi & Gamô 1992 Nebaliidae Antarctica Nebaliella caboti Clark 1932 Nebaliidae Cabot Strait, New Jersey Nebaliella declivatas Walker-Smith 1998 Nebaliidae Australia Nebaliella extrema Thiele 1905 Nebaliidae Antarctica Dahlella caldariensis Hessler 1984 Nebaliidae East Pacific Rise Sarsinebalia cristobi Moreira, Gestoso & Troncoso 2003 Nebaliidae north-east Atlantic Ocean Sarsinebalia typhlops 1870 Nebaliidae North Atlantic, Australia Sarsinebalia urgorrii Moreira, Gestoso & Troncoso 2003 Nebaliidae north-east Atlantic Ocean Speonebalia cannoni Bowman, Yager & Iliffe 1985 Nebaliidae Turks and Caicos Islands Levinebalia fortunata 1976 Paranebaliidae New Zealand Levinebalia maria Walker-Smith 2000 Paranebaliidae Australia Paranebalia belizensis Modlin 1991 Paranebaliidae Belize Paranebalia longipes 1875 Paranebaliidae Atlantic, Pacific and Indian Oceans Saronebalia guanensis Haney & Martin 2004 Paranebaliidae British Virgin Islands
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