Malacostraca

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{{Taxobox | color = pink | name = Malacostraca | image = Eoph_MagelaT_site2.jpg | image_width = 250px | image_caption = Eophreatoicus, a fresh water isopod from Australia. | regnum = Animalia | phylum = Arthropoda | subphylum = Crustacea | classis = Malacostraca | classis_authority = Latreille, 1802 | subdivision_ranks = Subclasses | subdivision = Eumalacostraca
Hoplocarida
Phyllocarida
See text for orders. }}

The Malacostraca (Greek: "soft shell") are the largest subgroup of crustaceans and include most of the animals that non-experts recognise as crustaceans, such as the decapods (such as crabs, mole crabs, lobsters and true shrimps), the stomatopods or mantis shrimps, and krills. They also include the huge group of amphipods, and the only substantial group of land-based crustaceans, the isopods (woodlice or sowbugs and related species). With more than 22,000 members, this group represents two third of all crustacean species and contains all the larger forms. It first 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.

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Morphology

Their characteristics include:

The head has 6 segments, with a pair of antennules and a pair of antennae, as well as mouthparts.
They have 5 pairs of walking legs, with the first often modified to form pincers.
There are 8 thoracic segments. The cephalothorax is covered by a carapace form via fusion of 3 of them, letting the 5 other uncovered.
The abdomen is behind and often used for swimming. There are 6 abdominal segments.
There are appendages near the mouthparts, these are called maxillipeds.
They have compound stalked or sessile eyes.
They have two-chambered stomach.
They have a centralised nervous system.

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Classification

Martin and DavisTemplate:Ref 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 Image:Mantis shrimp.jpg

†Order Archaeostraca
†Order Hoplostraca
Order Leptostraca Claus, 1880

Subclass Hoplocarida Calman, 1904

Order Stomatopoda Latreille, 1817 (mantis shrimps)

Subclass Eumalacostraca Grobben, 1892
- Superorder Syncarida Packard, 1885
  - †Order Palaeocaridacea
  - Order Bathynellacea Chappuis, 1915
  - Order Anaspidacea Calman, 1904 (including Stygocaridacea)
- Superorder Peracarida Calman, 1904 Image:ArmadillidiumVulgare.jpg
  - Order Spelaeogriphacea Gordon, 1957
  - Order Thermosbaenacea Monod, 1927
  - Order Lophogastrida Sars, 1870
  - Order Mysida Haworth, 1825
  - Order Mictacea Bowman, Garner, Hessler, Iliffe & Sanders, 1985
  - Order Amphipoda Latreille, 1816
  - Order Isopoda Latreille, 1817 (pillbugs, sowbugs, woodlice)
  - Order Tanaidacea Dana, 1849
  - Order Cumacea Krøyer, 1846
- Superorder Eucarida Calman, 1904
  - Order Euphausiacea Dana, 1852
  - Order Amphionidacea Williamson, 1973
  - Order Decapoda Latreille, 1802 (crabs, lobsters, shrimp)