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Groundwater isopods (Cruregens)

Taxonomic group

Paranthuridae: Cruregens

Diagnostic features

The freshwater paranthurid isopods have elongated bodies, making them look quite unlike the more familiar slater-shaped isopods. Cruregens is easily distinguished from the similar-shaped Paranthura by the absence of eyes (which are present in Paranthura). Cruregens also has little or no body pigmentation, unlike Paranthura.

Typical habitats

Cruregens is one of several pale, eyeless crustaceans known to live in groundwater, and they are infrequently recorded in streams.


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 of Cruregens 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).