SYSTEMATICS OF THE FRESH-WATER CRAYFISH GENUS CHERAX ERICHSON (DECAPODA, PARASTACIDAE) IN SOUTH-WESTERN AUSTRALIA - ELECTROPHORETIC, MORPHOLOGICAL AND HABITAT VARIATION

A detailed study of electrophoretic, morphological and habitat variati on amongst species of Cherax in south-western Australia supported the recognition of only five of the eight species currently recognised and revealed that morphological and habitat variation within these crayfi sh is more extensive and complicated than was previously realised. Wit hin several species morphological and habitat variation was found to b e as great as that between species. Furthermore, a major component of the morphological variability, both within and between species, was fo und to be associated with habitat variation. Three of the five species of Cherax recognised in this study correspond to the consistently rec ognised and widespread species, C. preissii Erichson, C. quinquecarina tus (Gray) and C. tenuimanus Smith. The two other species are C. crass imantus Riek and C. glaber Riek which have restricted distributions in the extreme south-west of Western Australia. The species C. glabriman us Riek and C. neocarinatus Riek could not be distinguished from C. qu inquecarinatus, nor could C. plebejus (Hess) be distinguished from C. preissii. On a general level, the results of this study question the v alue of morphological information in systematic studies of freshwater crayfish. Morphologically based taxonomic studies of freshwater crayfi sh need to be interpreted with caution because, firstly, taxonomic cha racters may be far more variable than realised; secondly, morphologica l and habitat differences cannot necessarily be equated with specific distinctions; and thirdly, genetically distinct species that occupy si milar habitats need not be morphologically distinct.