Leptostraca is an order

Order (biology)

In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...

 of small, marine crustacean

Crustacean

Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...

s. Its members, including the well-studied Nebalia

Nebalia

Nebalia is a genus of small crustaceans containing more than half of the species in the order Leptostraca, with around 30 species:*Nebalia abyssicola Ledoyer, 1997*Nebalia antarctica Dahl, 1990*Nebalia biarticulata Ledoyer, 1997...

, occur throughout the world's oceans and are usually considered to be filter-feeders

Filter feeder

Filter feeders are animals that feed by straining suspended matter and food particles from water, typically by passing the water over a specialized filtering structure. Some animals that use this method of feeding are clams, krill, sponges, baleen whales, and many fish and some sharks. Some birds,...

. It is the only extant order in the subclass

Class (biology)

In biological classification, class is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, order, family, genus, and species, with class fitting between phylum and order...

 Phyllocarida

Phyllocarida

Phyllocarida is a subclass of crustaceans, comprising the extant order Leptostraca and the extinct orders Hymenostraca and Archaeostraca....

. They are believed to represent the most primitive members of their class, the Malacostraca

Malacostraca

Malacostraca is the largest of the six classes of crustaceans, containing over 25,000 extant species, divided among 16 orders. Its members display a greater diversity of body forms than any other class of animals, and include crabs, lobsters, shrimp, krill, woodlice, scuds , mantis shrimp and many...

, and first appear in the fossil record during the Cambrian

Cambrian

The Cambrian is the first geological period of the Paleozoic Era, lasting from Mya ; it is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the Latin name for Wales, where Britain's...

 period.

Description

Leptostracans are usually small, typically 5 to 15 mm (0.196850393700787 to 0.590551181102362 ) long, crustaceans distinguished from all other members of their class in having seven abdominal

Abdomen

In vertebrates such as mammals the abdomen constitutes the part of the body between the thorax and pelvis. The region enclosed by the abdomen is termed the abdominal cavity...

 segments, instead of six. Their head has stalked compound eyes, two pairs of antennae

Antenna (biology)

Antennae in biology have historically been paired appendages used for sensing in arthropods. More recently, the term has also been applied to cilium structures present in most cell types of eukaryotes....

 (one biramous, one uniramous), and a pair of mandibles but no maxillipeds. The carapace

Carapace

A carapace is a dorsal section of the exoskeleton or shell in a number of animal groups, including arthropods such as crustaceans and arachnids, as well as vertebrates such as turtles and tortoises. In turtles and tortoises, the underside is called the plastron.-Crustaceans:In crustaceans, the...

 is large and comprises two valves which cover the head and the thorax, including most of the thoracic appendages, and serves as a brood pouch for the developing embryo

Embryo

An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...

s. 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.

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

Malacostraca

Malacostraca is the largest of the six classes of crustaceans, containing over 25,000 extant species, divided among 16 orders. Its members display a greater diversity of body forms than any other class of animals, and include crabs, lobsters, shrimp, krill, woodlice, scuds , mantis shrimp and many...

, and the sister group to Leptostraca is Eumalacostraca

Eumalacostraca

The Eumalacostraca are a subclass of crustaceans, containing almost all living malacostracans, about 40,000 described species. The remaining subclasses are the Phyllocarida and possibly the Hoplocarida or mantis shrimps....

.

The Order Leptostraca is divided into three families

Family (biology)

In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

, with ten genera

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 containing a total of around 40 validky described extant species:

Species	Authority	Date	Family	Distribution
Nebaliopsis typica Nebaliopsis Nebaliopsis typica is a species of leptostracan crustacean, the only species in the genus Nebaliopsis. It is exceptionally large for a leptostracan, at up to in length, compared to for the other species...	Sars	1887	Nebaliopsididae	Southern Hemisphere Southern Hemisphere The Southern Hemisphere is the part of Earth that lies south of the equator. The word hemisphere literally means 'half ball' or "half sphere"...
Pseudonebaliopsis atlantica	Petryachov	1996	Nebaliopsididae	North Atlantic
Nebalia antarctica	Dahl	1990	Nebaliidae	Antarctica
Nebalia bipes Nebalia bipes Nebalia bipes is a species of leptostracan crustacean, and the first species in the order to have been described . It lives in coastal waters at depths of , under stones or among decaying organic matter where it is common and sometimes abundant. Its predators include the fish Merlangius merlangus...	Fabricius	1780	Nebaliidae	Arctic and sub-Arctic Arctic Ocean The Arctic Ocean, located in the Northern Hemisphere and mostly in the Arctic north polar region, is the smallest and shallowest of the world's five major oceanic divisions...
Nebalia borealis	Dahl	1985	Nebaliidae	north-east Atlantic Ocean Atlantic Ocean The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
Nebalia brucei	Olesen	1999	Nebaliidae	Tanzania Tanzania The United Republic of Tanzania is a country in East Africa bordered by Kenya and Uganda to the north, Rwanda, Burundi, and the Democratic Republic of the Congo to the west, and Zambia, Malawi, and Mozambique to the south. The country's eastern borders lie on the Indian Ocean.Tanzania is a state...
Nebalia cannoni	Dahl	1990	Nebaliidae	South Georgia
Nebalia capensis	Barnard	1914	Nebaliidae	South Africa South Africa The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
Nebalia clausi	Dahl	1985	Nebaliidae	Italy Italy Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...
Nebalia dahli	Kazmi & Tirmizi	1989	Nebaliidae	Pakistan Pakistan Pakistan , officially the Islamic Republic of Pakistan is a sovereign state in South Asia. It has a coastline along the Arabian Sea and the Gulf of Oman in the south and is bordered by Afghanistan and Iran in the west, India in the east and China in the far northeast. In the north, Tajikistan...
Nebalia daytoni	Vetter	1996	Nebaliidae	California California California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
Nebalia falklandensis	Dahl	1990	Nebaliidae	Falkland Islands Falkland Islands The Falkland Islands are an archipelago in the South Atlantic Ocean, located about from the coast of mainland South America. The archipelago consists of East Falkland, West Falkland and 776 lesser islands. The capital, Stanley, is on East Falkland...
Nebalia geoffroyi	Milne-Edwards	1828	Nebaliidae	north-east Atlantic Ocean Atlantic Ocean The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
Nebalia gerkenae	Haney & Martin	2000	Nebaliidae	California California California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
Nebalia herbstii Nebalia herbstii Nebalia herbstii is a leptostracan found in the north east Atlantic, including Galway Bay, Ireland. It is found in the intertidal zone in sandy and rocky shores. Total lengths are usually in the range of . N...	Leach	1814	Nebaliidae	north-east Atlantic Ocean Atlantic Ocean The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
Nebalia hessleri	Martin et al.	1996	Nebaliidae	California California California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
Nebalia ilheoensis	Kensley	1976	Nebaliidae	south-western Africa South West Africa South-West Africa was the name that was used for the modern day Republic of Namibia during the earlier eras when the territory was controlled by the German Empire and later by South Africa....
Nebalia kensleyi	Haney & Martin	2005	Nebaliidae	California California California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
Nebalia kocatasi	Kocak, Moreira & Katagan	2007	Nebaliidae	Mediterranean Sea Mediterranean Sea The Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by North Africa, and on the east by the Levant...
Nebalia lagartensis	Escobar & Villalobos-Hiriart	1995	Nebaliidae	Mexico Mexico The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
Nebalia longicornis	Thomson	1879	Nebaliidae	South Pacific Pacific Ocean The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World... , South Africa South Africa The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans... , Caribbean Sea Caribbean Sea The Caribbean Sea is a sea of the Atlantic Ocean located in the tropics of the Western hemisphere. It is bounded by Mexico and Central America to the west and southwest, to the north by the Greater Antilles, and to the east by the Lesser Antilles....
Nebalia marerubi	Wägele	1983	Nebaliidae	Red Sea Red Sea The Red Sea is a seawater inlet of the Indian Ocean, lying between Africa and Asia. The connection to the ocean is in the south through the Bab el Mandeb strait and the Gulf of Aden. In the north, there is the Sinai Peninsula, the Gulf of Aqaba, and the Gulf of Suez...
Nebalia patagonica	Dahl	1990	Nebaliidae	Magellan region
Nebalia schizophthalma	Haney, Hessler & Martin	2001	Nebaliidae	western Atlantic Ocean Atlantic Ocean The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
Nebalia strausi	Risso	1826	Nebaliidae	north-east Atlantic Ocean Atlantic Ocean The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area... , Mediterranean Sea Mediterranean Sea The Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by North Africa, and on the east by the Levant...
Nebalia troncosoi	Moreira, Cacabelos & Dominguez	2003	Nebaliidae	Spain Spain Spain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...
Nebaliella antarctica	Thiele	1904	Nebaliidae	Kerguelen Kerguelen Islands The Kerguelen Islands , also known as the Desolation Islands, are a group of islands in the southern Indian Ocean constituting the emerged part of the otherwise submerged Kerguelen Plateau. The islands, along with Adélie Land, the Crozet Islands and the Amsterdam and Saint Paul Islands are part of... , New Zealand New Zealand New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
Nebaliella brevicarinata	Kikuchi & Gamô	1992	Nebaliidae	Antarctica
Nebaliella caboti	Clark	1932	Nebaliidae	Cabot Strait Cabot Strait Cabot Strait is a strait in eastern Canada approximately 110 kilometres wide between Cape Ray, Newfoundland and Cape North, Cape Breton Island. It is the widest of the three outlets for the Gulf of Saint Lawrence into the Atlantic Ocean, the others being the Strait of Belle Isle and Strait of Canso... , New Jersey New Jersey New Jersey is a state in the Northeastern and Middle Atlantic regions of the United States. , its population was 8,791,894. It is bordered on the north and east by the state of New York, on the southeast and south by the Atlantic Ocean, on the west by Pennsylvania and on the southwest by Delaware...
Nebaliella declivatas	Walker-Smith	1998	Nebaliidae	Australia Australia Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
Nebaliella extrema	Thiele	1905	Nebaliidae	Antarctica
Dahlella caldariensis Dahlella Dahlella caldariensis is a species of leptostracan crustacean which lives on hydrothermal vents in the Pacific Ocean.-Description:Dahlella may reach a length of from the base of the rostrum to the end of the abdomen...	Hessler	1984	Nebaliidae	East Pacific Rise East Pacific Rise The East Pacific Rise is a mid-oceanic ridge, a divergent tectonic plate boundary located along the floor of the Pacific Ocean. It separates the Pacific Plate to the west from the North American Plate, the Rivera Plate, the Cocos Plate, the Nazca Plate, and the Antarctic Plate...
Sarsinebalia cristobi	Moreira, Gestoso & Troncoso	2003	Nebaliidae	north-east Atlantic Ocean Atlantic Ocean The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
Sarsinebalia typhlops		1870	Nebaliidae	North Atlantic, Australia Australia Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
Sarsinebalia urgorrii	Moreira, Gestoso & Troncoso	2003	Nebaliidae	north-east Atlantic Ocean Atlantic Ocean The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
Speonebalia cannoni	Bowman, Yager & Iliffe	1985	Nebaliidae	Turks and Caicos Islands Turks and Caicos Islands The Turks and Caicos Islands are a British Overseas Territory and overseas territory of the European Union consisting of two groups of tropical islands in the Caribbean, the larger Caicos Islands and the smaller Turks Islands, known for tourism and as an offshore financial centre.The Turks and...
Levinebalia fortunata		1976	Paranebaliidae	New Zealand New Zealand New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
Levinebalia maria	Walker-Smith	2000	Paranebaliidae	Australia Australia Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
Paranebalia belizensis	Modlin	1991	Paranebaliidae	Belize Belize Belize is a constitutional monarchy and the northernmost country in Central America. Belize has a diverse society, comprising many cultures and languages. Even though Kriol and Spanish are spoken among the population, Belize is the only country in Central America where English is the official...
Paranebalia longipes		1875	Paranebaliidae	Atlantic Atlantic Ocean The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area... , Pacific Pacific Ocean The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...  and Indian Ocean Indian Ocean The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and... s
Saronebalia guanensis	Haney & Martin	2004	Paranebaliidae	British Virgin Islands British Virgin Islands The Virgin Islands, often called the British Virgin Islands , is a British overseas territory and overseas territory of the European Union, located in the Caribbean to the east of Puerto Rico. The islands make up part of the Virgin Islands archipelago, the remaining islands constituting the U.S...