THE XERCES SOCIETY FOR INVERTEBRATE CONSERVATION

Aquatic Invertebrates in Pacific Northwest Freshwater Wetlands
An Identification Guide and Educational Resource

These two uncommon genera are very difficult to distinguish when they are immature. They are primarily hyporheic. If you encounter small isopods that are eyeless and don't have body pigment, it's most likely one of these genera. They may be separated spatially, with Salmasellus farther north and east (Montana, Alberta) and the Calasellus more southern and western (California). Though because the hyporheic zone is so poorly understood, both may be widely distributed in the Northwest.