Malacostraca

The Malacostraca (Greek: "soft shell") are the largest class of crustaceans and include most of the animals that non-experts recognize as crustaceans, including decapods (such as crabs, lobsters and shrimp), stomatopods (mantis shrimp) and euphausiids (krill). They also include the amphipods and the only substantial group of land-based crustaceans, the isopods (woodlice and related species). With more than 22,000 members, this group represents two thirds of all crustacean species and contains all the larger forms. The first malacostracans appeared in the Cambrian.

The classification of crustaceans is currently being debated, and the Malacostraca are regarded by some authors as a class and by others as a subclass.

The phylogeny of this group of organisms is debated . Recent molecular studies (18S  and 28S ) have even disputed the monophyly of the Peracarida by removing the Mysida and have firmly disproven the monophyly of the Edriophthalma (Isopoda and Amphipoda) and the Mysidacea (Mysida, Lophogastrida and Pygocephalomorpha).

Morphology

] Their characteristics include: 3 tagmata: Head (5 segments), thorax (8 segments) and abdomen (6 segments (7 segments in Phyllocarida)).
The head has 5 segments, with a pair of antennules and a pair of antennae, as well as 3 mouthparts, comprising the mandibles, the maxillula and the maxilla.
There are 8 thoracic segments. The cephalothorax is covered by a carapace form via fusion of 3 of them, letting the 5 other uncovered.
They usually have 8 pairs of thoracic legs (thoracopods), of which the first pair or several pairs are often modified into feeding appendages called maxillipeds. The first pair of legs behind the maxillipeds is often modified into pincers.
The abdomen has 6 segments (7 segments in Phyllocarida). The appendages are called pleopods and are usually natatory. In Isopoda the pleopods are used for respiration.
Fixation of gonopores on 6th segment for the female and on the 8th segment for the male.
They have compound stalked or sessile eyes.
They have a two-chambered stomach.
They have a centralized nervous system.

Classification

Martin and Davis  present the following classification of living malacostracans into orders, to which extinct orders have been added, indicated by †.

Class Malacostraca Latreille, 1802 Subclass Phyllocarida Packard, 1879
†Order Archaeostraca
†Order Hoplostraca
†Order Canadaspidida
Order Leptostraca Claus, 1880
Subclass Hoplocarida Calman, 1904
Order Stomatopoda Latreille, 1817 (mantis shrimp)
Subclass Eumalacostraca Grobben, 1892
Superorder Syncarida Packard, 1885
†Order Palaeocaridacea
Order Bathynellacea Chappuis, 1915
Order Anaspidacea Calman, 1904
Superorder Peracarida Calman, 1904
Order Spelaeogriphacea Gordon, 1957
Order Thermosbaenacea Monod, 1927
Order Lophogastrida Sars, 1870
Order Mysida Haworth, 1825 (opossum shrimp)
Order Mictacea Bowman, Garner, Hessler, Iliffe & Sanders, 1985
Order Amphipoda Latreille, 1816
Order Isopoda Latreille, 1817 (including woodlice, slaters)
Order Tanaidacea Dana, 1849
Order Cumacea Krøyer, 1846 (hooded shrimp)
Superorder Eucarida Calman, 1904
Order Euphausiacea Dana, 1852 (krill)
Order Amphionidacea Williamson, 1973
Order Decapoda Latreille, 1802 (crabs, lobsters, shrimp and others)

Translation

The word "Malacostraca" occurs as such in the following languages: English, Spanish, French, Italian, Latin, Dutch, Portuguese, Simple English.

Translation(s) in other languages: Bulgarian: Висши ракообразни, Catalan: Malacostraci, Danish: Storkrebs, German: Höhere Krebse, Estonian: Kõrgemad vähid, Greek: Μαλακόστρακα, Esperanto: Malakostrakoj, Korean: 연갑강, Hebrew: סרטנים עילאיים, Latvian: Augstākie vēži, Lithuanian: Aukštesnieji vėžiagyviai, Hungarian: Felsőbbrendű rákok, Japanese: 軟甲綱, Norwegian (Bokmål): Storkreps, Norwegian (Nynorsk): Storkreps, Polish: Pancerzowce, Romanian: Rac, Quechua: Pura-pura qara, Russian: Высшие раки, Slovenian: Višji raki, Finnish: Kuoriäyriäiset, Swedish: Storkräftor, Tongan: ʻUo moʻoni, Ukrainian: Вищі раки, Chinese: 软甲纲.