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 Major Groups | Crustacea (crustaceans) | Malacostraca (malacostracans)

Malacostraca (malacostracans)

Major Group: Crustacea
Minor Group: Malacostraca
The Malacostraca are the largest and most diverse class of subphylum Crustacea. Several malacostracan species are important in aquaculture and food industries. Of the three subclasses, Phyllocarida, Hoplocarida and Eumalacostraca, only Eumalacostraca contains freshwater species. Whilst crustaceans as a whole display highly variable body forms, malacostracans display a single type of basic body structure.

Descriptive Features:

  • single carapace, fused dorsally
  • head typically with paired compound eyes, usually at ends of movable stalks, but occasionally greatly reduced or lacking, and/or stalks immovable
  • 5 head (cephalic), 8 thoracic (thoracomeres) and 6 abdominal (pleomeres) segments
  • 5 pairs of cephalic appendages including: biramous antennules, antennae with flattened scale-like exopod, mandibles, maxillules, and maxillae
  • 5 pairs of thoracic appendages, segmented legs with claws
  • pleopods usually present, 6th pair (and sometimes others) differentiated into uropods
  • uropods may form a tail fan with telson, attached to end of pleon
  • Total length: up to 40 mm
    • Taxonomic Checklist: Orders
      Amphipoda (side swimmers)
      Bathynellacea (underground waters)
      Decapoda (yabbies plus)
      Isopoda (water slaters)
      Spelaeogriphacea (underground waters)
      Tanaidacea (underground waters)
      Thermosbaenacea (underground waters)

      Distribution: Australia wide

      Sensitivity Rating: SIGNAL grades from 2 to 6. Some freshwater species are euryhaline, tolerating salinity levels as high as 30%.

      Functional Feeding Group: shredders, gathering collectors, scrapers, parasites, filtering collectors, predators

      Ecology: Instream habitat: Almost every freshwater habitat is utilised by a malacostracan species, in both lotic and lentic surface waters and some uniquely in underground waters. Surface waters include; streams flowing to and through open grasslands, swamps and forested areas; permanent and temporary pools, pools in the downfall of a waterfall; ditches, waterholes, billabongs and lakes; ephemeral creeks, creeks subject to seasonal torrential flow; springs and interstitial waters. Many substrata types are inhabited, including rock, sand, peaty sand, clay, mud and gravel. Malacostracans tend to prefer the littoral zones of water bodies, especially well vegetated areas. They can be found in packs of leaf litter, under rotting logs, under stones, amongst plant roots and burrowing into the substratum. Some species are semi-aquatic being found in Sphagnum moss and in vegetation held water.
      Feeding ecology: Free living malacostracans are omnivores, predators, detritivores, herbivores and filter feeders.
      Habit: Many malacostracan species are burrowers. The burrows are connected to open waters or the water table. Some burrows are long, meandering 20-30 cm into the bank whilst others are short burrows or form a catacomb of holes in the soft stream banks. If the water dries out the burrows are sealed with a mud chimney. Malacostracans may be nocturnal or diurnal. They are mostly free living but may also be commensal or ectoparasitic.
      Life history:








      Information Sources: Davie 2002, Davie 2002a, Lowry & Stoddart 2003, Poore 2002, Guzik et al. 2008 
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