A detailed study of electrophoretic, morphological and habitat variation 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 crayfish is more extensive and complicated than was previously realised. Within several species morphological and habitat variation was found to be as great as that between species. Furthermore, a major component of the morphological variability, both within and between species, was found to be associated with habitat variation. Three of the five species of Cherax recognised in this study correspond to the consistently recognised and widespread species, C. preissii Erichson, C. quinquecarinatus (Gray) and C. tenuimanus Smith. The two other species are C. crassimantus Riek and C. glaber Riek which have restricted distributions in the extreme south-west of Western Australia. The species C. glabrimanus Riek and C. neocarinatus Riek could not be distinguished from C. quinquecarinatus, nor could C. plebejus (Hess) be distinguished from C. preissii. On a general level, the results of this study question the value of morphological information in systematic studies of freshwater crayfish. Morphologically based taxonomic studies of freshwater crayfish need to be interpreted with caution because, firstly, taxonomic characters may be far more variable than realised; secondly, morphological and habitat differences cannot necessarily be equated with specific distinctions; and thirdly, genetically distinct species that occupy similar habitats need not be morphologically distinct.

Abstract. Crustaceans in the class Branchiopoda exhibit a wide range of breeding systems, including dioecy (gonochorism), androdioecy, parthenogenesis, cyclic parthenogenesis, and hermaphroditism. The largest subgroup of the Branchiopods, the Diplostraca, is reported to encompass all five of these breeding systems. However, many of these reports are based primarily on simple observations of sex ratios in natural populations. Herein we report the beginnings of a more rigorous approach to breeding system determination in the Diplostraca, starting with the family Limnadiidae. We combine measurements of sex ratio, offspring rearings, and behavior to identify three breeding systems within the Limnadiidae: dioecy, androdioecy, and selfing hermaphroditism. To date, no instances of parthenogenetic reproduction have been identified in this family. Comparisons of breeding system determination via simple population sex ratios with our more controlled studies show that simple sex ratios can be useful when these sex ratios are ∼50% males (=dioecy) or 5–30% males (androdioecy). However, population sex ratios of 0–5% males or 35–45% males necessitate further investigation because estimates in these ranges cannot distinguish selfing hermaphroditism from androdioecy or androdioecy from dioecy, respectively. We conclude by noting that the genetic sex‐determining system outlined for one of these limnadiid species, Eulimnadia texana, provides a parsimonious framework to describe the evolution of the three breeding systems observed within the Limnadiidae.

Among the variety of reproductive mechanisms exhibited by living systems, one permutationandrodioecy (mixtures of males and hermaphrodites)-is distinguished by its rarity. Models of mating system evolution predict that androdioecy should be a brief stage between hermaphroditism and dioecy (separate males and females), or vice versa. Herein we report evidence of widespread and ancient androdioecy in crustaceans in the genus Eulimnadia, based on observations of over 33 000 shrimp from 36 locations from every continent except Antarctica. Using phylogenetic, biogeographical and palaeontological evidence, we infer that androdioecy in Eulimnadia has persisted for 24-180 million years and has been maintained through multiple speciation events. These results suggest that androdioecy is a highly successful aspect of the life history of these freshwater crustaceans, and has persisted for orders of magnitude longer than predicted by current models of this rare breeding system.

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External and internal feeding structures of the pelagic final phyllosoma, the transitional puerulus, and the benthic juvenile Western Rock Lobster, Panulirus cygnus, were studied by means of scanning electron microscopy. The study revealed that the external feeding structures of phyllosomata are well equipped for capture and mastication of food. The foregut, however, is not clearly divided into pyloric and cardiac regions and a gastric mill is absent, although a comb row and gland filter are present. Juveniles, on the other hand, have a well-developed gastric mill and gastric teeth, and a cardiopyloric valve separates the foregut into cardiac and pyloric regions. External mouthparts of juveniles are suitable for mastication of solid food particles and bear numerous setae. In contrast, external mouthparts of pueruli are largely non-setose. Furthermore, although the foregut is differentiated into pyloric and gastric regions and a gland filter and comb row are present, a functional gastric mill is absent during the puerulus stage. Absence of such structures indicates that the puerulus may be a non-feeding stage. It is postulated that absence of (or reduced) feeding may be a response to an increased risk of predation rather than a result of the considerable morphological changes taking place during the transition from a planktonic to a benthic lifestyle, as has been previously proposed. © 1994 Wiley-Liss, Inc.