Leptostraca

Leptostraca (from the Greek words for thin and shell)^[3] 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.^[4] 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.^[5]

Leptostraca Temporal range: Cambrian–Recent PreꞒ Ꞓ O S D C P T J K Pg N
Nebalia bipes
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Malacostraca
Subclass:	Phyllocarida
Order:	Leptostraca Claus, 1880 [1]
Families [2]
Nebaliidae Nebaliopsididae Paranebaliidae † Rhabdouraeidae

Description

Diagram of Nebalia reboredae^[6] showing the major features of the external anatomy: 1: antennule; 2: rostrum; 3: carapace; 4: abdomen / pleon; 5: furca; 6: telson; 7: pleopods; 8: antenna; 9: thoracopods; 10: eye

Leptostracans are usually small, typically 5 to 15 millimetres (0.2 to 0.6 in) long,^[7] but the largest species (Nebaliopsis typica) can reach 4 cm, and the Silurian Ceratiocaris could grow to 75 cm.^[8] 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.^[4] 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.^[9][10][11]

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.^[5]

Classification

It is now accepted that leptostracans belong to the Malacostraca,^[12] and the sister crown group to Leptostraca is Eumalacostraca.^[13]

The order Leptostraca is divided into three families, with ten genera containing a total of around 40 validly described extant species:^[14]

Species	Authority	Date	Family	Distribution
Nebaliopsis typica	Sars	1887	Nebaliopsididae	Southern Hemisphere [2]
Pseudonebaliopsis atlantica	Petryachov	1996	Nebaliopsididae	North Atlantic [15]
Nebalia antarctica	Dahl	1990	Nebaliidae	Antarctica [2]
Nebalia bipes	Fabricius	1780	Nebaliidae	Arctic and sub-Arctic [2]
Nebalia borealis	Dahl	1985	Nebaliidae	north-east Atlantic Ocean [2]
Nebalia brucei	Olesen	1999	Nebaliidae	Tanzania [2]
Nebalia cannoni	Dahl	1990	Nebaliidae	South Georgia [2]
Nebalia capensis	Barnard	1914	Nebaliidae	South Africa [2]
Nebalia clausi	Dahl	1985	Nebaliidae	Italy [2]
Nebalia dahli	Kazmi & Tirmizi	1989	Nebaliidae	Pakistan [2]
Nebalia daytoni	Vetter	1996	Nebaliidae	California [2]
Nebalia falklandensis	Dahl	1990	Nebaliidae	Falkland Islands
Nebalia geoffroyi	Milne-Edwards	1828	Nebaliidae	north-east Atlantic Ocean [16]
Nebalia gerkenae	Haney & Martin	2000	Nebaliidae	California [2]
Nebalia herbstii	Leach	1814	Nebaliidae	north-east Atlantic Ocean [2]
Nebalia hessleri	Martin et al.	1996	Nebaliidae	California [2]
Nebalia ilheoensis	Kensley	1976	Nebaliidae	south-western Africa [2]
Nebalia kensleyi	Haney & Martin	2005	Nebaliidae	California [17]
Nebalia kocatasi	Kocak, Moreira & Katagan	2007	Nebaliidae	Mediterranean Sea [18]
Nebalia koreana	Song, Moreira & Min	2012	Nebaliidae	South Korea [19]
Nebalia lagartensis	Escobar & Villalobos-Hiriart	1995	Nebaliidae	Mexico [2]
Nebalia longicornis	Thomson	1879	Nebaliidae	South Pacific, South Africa, Caribbean Sea [2]
Nebalia marerubi	Wägele	1983	Nebaliidae	Red Sea [2]
Nebalia patagonica	Dahl	1990	Nebaliidae	Magellan region [2]
Nebalia schizophthalma	Haney, Hessler & Martin	2001	Nebaliidae	western Atlantic Ocean [20]
Nebalia strausi	Risso	1826	Nebaliidae	north-east Atlantic Ocean, Mediterranean Sea [2]
Nebalia troncosoi	Moreira, Cacabelos & Dominguez	2003	Nebaliidae	Spain [21]
Nebaliella antarctica	Thiele	1904	Nebaliidae	Kerguelen, New Zealand [2]
Nebaliella brevicarinata	Kikuchi & Gamô	1992	Nebaliidae	Antarctica [2]
Nebaliella caboti	Clark	1932	Nebaliidae	Cabot Strait, New Jersey [2]
Nebaliella declivatas	Walker-Smith	1998	Nebaliidae	Australia [2]
Nebaliella extrema	Thiele	1905	Nebaliidae	Antarctica [2]
Dahlella caldariensis	Hessler	1984	Nebaliidae	East Pacific Rise [2]
Sarsinebalia cristobi	Moreira, Gestoso & Troncoso	2003	Nebaliidae	north-east Atlantic Ocean [22]
Sarsinebalia typhlops	(Sars)	1870	Nebaliidae	North Atlantic, Australia [2]
Sarsinebalia urgorrii	Moreira, Gestoso & Troncoso	2003	Nebaliidae	north-east Atlantic Ocean [22]
Speonebalia cannoni	Bowman, Yager & Iliffe	1985	Nebaliidae	Turks and Caicos Islands [2]
Levinebalia fortunata	(Wakabara)	1976	Paranebaliidae	New Zealand [2]
Levinebalia maria	Walker-Smith	2000	Paranebaliidae	Australia [2]
Paranebalia belizensis	Modlin	1991	Paranebaliidae	Belize [2]
Paranebalia longipes	(Willemöes-Suhm)	1875	Paranebaliidae	Atlantic, Pacific and Indian Oceans [2]
Saronebalia guanensis	Haney & Martin	2004	Paranebaliidae	British Virgin Islands [23]