Freshwater species in general (and crayfish specifically) often have limited ranges with high species endemism within, and species turnover between, catchments. Freshwater species also face ever-increasing threats, and genetic diversity (both at and below the species level) is being lost as a result of these threats. Molecular taxonomy provides a tool by which this diversity can be rapidly (and relatively cheaply) uncovered before it is lost. Identifying previously unrealised diversity within crayfish via molecular techniques can act as a stimulus to further taxonomic investigations and conservation efforts. Specific examples are given from Australian crayfish, where molecular data have highlighted significant genetic diversity, which may correspond to previously overlooked morphological variation. We hope these examples can promote the undertaking of wide scale molecular revisions of as many crayfish taxa as possible, looking for any previously unrecognised lineages within currently described species (akin to ESUs) that warrant further revision. Beyond this, we advocate that these lineages should be afforded conservation consideration in order to buy time for more thorough reviews to be completed.