Malacostraca

Malacostraca Fossil range: 542–0 Ma PreЄ Є O S D C P T J K Pg N
Scientific classification
Kingdom: Animalia Phylum: Arthropoda Subphylum: Crustacea Class: Malacostraca Latreille, 1802
Subclasses
Eumalacostraca Hoplocarida Phyllocarida See text for orders.

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 ^[1]. Recent molecular studies (18S ^[2] and 28S ^[3]) 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

General malacostracan Bauplan

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

Lysiosquillina maculata, a mantis shrimp (Stomatopoda)

Armadillidium vulgare, an isopod

Martin and Davis ^[4] 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)

References

Wikispecies has information related to: Malacostraca

Wikimedia Commons has media related to: Malacostraca

External links

• Malacostraca image key - Guide to the marine zooplankton of south eastern Australia, Tasmanian Aquaculture and Fisheries Institute