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Groundwater isopods (Phreatoicidae)

Taxonomic group

Family: Phreatoicidae

Diagnostic features

The phreatoicids are among the isopod groups that include species specialised to living in groundwater. They differ from most isopods in being laterally compressed (as if squashed from the sides) giving them an amphipod-like appearance. As is typical of groundwater invertebrates, they have little or no body pigmentation, and no visible eye.

Typical habitats

Phreatoicids are common in some South Island streams, presumably where is inflow from groundwater aquifers that support these isopods.


Being groundwater invertebrates, they presumably feed on bacterial biofilms.

Indicator value

  • Hard bottom: unassigned; Order Isopoda value 5
  • Soft bottom: unassigned; Order Isopoda value 4.5

The tolerance values (ranging from 0 to 10) give an indication of which are the sensitive taxa (values of 8 or more) and which are the tolerant taxa (values of 3 or less). For more information see: Indicator species

The occurrence phreatoicids in streams indicates a connection to interesting groundwater communities, but may indicate little about stream water quality. There are no tolerance values assigned to this genus but the Order Isopoda has been assigned tolerance values of 5 (hard bottom sites) and 4.5 (soft bottom sites).