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 Major Groups | Crustacea (crustaceans) | Malacostraca (malacostracans) | Isopoda (water slaters)

Isopoda (water slaters)

Major Group: Crustacea
Minor Group: Malacostraca
Order: Isopoda

Descriptive Features:

  • free living forms: diverse range of body forms, typically dorsoventrally flattened but may also be cylindrical or laterally compressed
  • parasitic forms: body forms varied
  • carapace absent
  • thoracomere 1 fused to head (bearing maxillipeds)
  • eyes sessile
  • antenna 1 typically uniramous, antenna 2 uniramous or with small exopod
  • maxillipedal basis with mesial endite distally directed, epipod lateral
  • thoracopods 2-8 (pereopods 1-7) uniramous, coxae with dorsal plates sometimes fused to tergites (on pereopod 1 almost always so), sometimes with ventral plates
  • pleopods 1-5 usually biramous, respiratory
  • 6th pleonal limb modified as uropod
  • telson fused to pleonite 6
  • Total length:  
  • Taxonomic Checklist:


    Microparasellidae (underground waters)
    Tainisopidae (underground waters)

    Distribution: Australia wide

    Sensitivity Rating: SIGNAL grade 2

    Functional Feeding Group: shredders, predators (parasites)

    Ecology: Instream habitat: Isopoda species occur in lotic and lentic surface waters including streams in forested areas, lakes, springs, swamps and even in ditches. Some species also inhabit estuarine waters or the underground water of caves. Generally freshwater slaters are found under stones or in the interstitial waters of rocky streams and in muddy areas either amongst roots of macrophytes or in burrows in the stream bank. Some species are semi-aquatic, living in Sphagnum moss and liverworts in boggy areas. Hypsimetopus intrusor (Hypsimetopidae) has a commensal relationship, cohabiting in burrows, with the Decapoda species, Engaeus canicularius (Parastacidae).
    Feeding ecology: Isopoda species are mostly detritivores and shredders, however some species are parasitic or ectoparasitic on shrimp, prawns or fish.
    Habit: Many phreatoicidean species (Amphisopidae, Hypsimetopidae, Phreatoicidae, Phreatoicopsidae) are curled under at the end. This spiny posterior is used to push them through the cryptic habitats they favour. The ‘head to toe’ curl is typically a resting or defensive position.
    Life history: Isopoda sexes are separate. Insemination is internal and the females incubate the eggs in a brood pouch for a length of time seemingly determined by environmental factors. Young water slaters are released from the brood pouch in a form similar to that of the adults but without pereopod 7. There is no larval stage or resistant egg stage. Some phreatoicidean isopods are able to avoid dry conditions by burrowing into the moist deeper layers of the streambed.
    Information Sources: Wilson 2003, 2012, Poore 2002, Williams 1980, Gooderham & Tsyrlin 2002

    Note: Anthuridae, Cirolanidae, Sphaeromatidae and Styloniscidae not included, as they are not noted as freshwater families occurring in Australia in Zoological Catalogue (Poore 2002). These families were included in Horwitz 1995.

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