Malacostraca

The Malacostraca (Greek: "soft shell") are the largest subgroup of crustaceans. They include decapods (such as crabs, lobsters and shrimp), stomatopods (mantis shrimp) and krill. There are 22,000 members in this group. It represents two thirds of all crustacean species. The first malacostracans appeared in the Cambrian period.

Malacostraca
Eophreatoicus, a fresh water isopod from Australia.
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Subphylum:	Crustacea
Class:	Malacostraca Latreille, 1802
Subclasses
Eumalacostraca Hoplocarida Phyllocarida See text for orders.

The classification of crustaceans is currently being debated. Some think Malacostraca is a class and others think it is a subclass.

Morphology

General malacostracan layout

Malacostraca have heads with six segments. They have a pair of antennules and a pair of antennae. They also have mouthparts. There are appendages near the mouthparts, called maxillipeds. They have five pairs of walking legs. The first pair is formed like a pincer. There are eight thoracic segments. There are six abdominal segments. They are used for swimming. Members of Malacostraca have compound stalked or sessile eyes. They have a two-chambered stomach and a centralized nervous system.

Classification

Lysiosquilla maculata, a mantis shrimp

Armadillidium vulgare, an isopod

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
    • Order Mictacea Bowman, Garner, Hessler, Iliffe & Sanders, 1985
    • Order Amphipoda Latreille, 1816
    • Order Isopoda Latreille, 1817 (woodlice, slaters)
    • 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)