The family Parastacidae contains all freshwater crayfish found naturally occurring in the southern hemisphere. Although widespread, with representatives occurring in South America, Madagascar (Fig. 2), and New Zealand, the family achieves by far its greatest diversity within Australia (Fig. 1). Over 85% of the known species of parastacid crayfish are from Australia. Similarly, nine of the 14 genera presently recognized within the Parastacidae are restricted to the Australian continent and nearby islands (including southern New Guinea) (Hobbs, 1988; Hobbs, 1991). The Australian freshwater crayfish fauna is unique and highly diverse, both in terms of species richness and in ecological and morphological diversity. This fauna contains the largest known freshwater invertebrate (Astacopsis gouldi [Clark]) and the highly evolved "land crayfishes" (e.g. Engaeus) which are able to complete their entire life cycle independent of surface water. In terms of the number of species, morphological variability, and ecological diversity, Australia's freshwater crayfish fauna is rivalled only by that found in the south east of the USA (for examples of Australian crayfish diversity, see Merrick, 1993).
Evolution and Systematics
Discussion of Phylogenetic Relationships
Studies of phylogenetic relationships among genera of parastacid crayfish to date have been of limited scope (Riek, 1969; Riek, 1972; Patak & Baldwin, 1984; Patak et al., 1989; Austin, 1995; Crandall et al. 1995) and have produced conflicting results using a variety of approaches and data sets. Riek (1969) presented the first systematic hypothesis for the relationships among the Australian genera (presented here). This hypothesis was based on features of the male genitalia, cephalothorax, and chelae as well as body shape (Riek, 1969). Subsequent to this study, Riek (1972) proposed an alternative interpretation with the additional characters associated with the cephalothoracic grooves and orientation of the chelae. This latter hypothesis added the genera Gramastacus and Paranephrops to the phylogeny and shifted the association of Parastacoides from the Euastacus-Astacopsis clade to the Cherax clade.
The two major clades proposed by Riek (1972) form two ecologically distinct groups; Engaeus, Engaewa, and Tenuibranchiurus form the first group, representing strong burrowers in which the fingers of the chelae move in a vertical plane; Euastacus, Astacopsis, Gramastacus, Geocharax, Parastacoides, Paranephrops, and Cherax comprise the second group of moderate burrowers in which the fingers of the chelae move largely or completely in a horizontal plane.
Patak and Baldwin (1984) applied electrophoretic and immunochemical comparisons of haemocyanins to infer phylogenetic relationships among a subset of the Australian genera. These biochemical techniques generated a hypothesis that differed from that of Riek (1972) in that the Geocharax-Gramastacus clade was clustered with the genus Engaeus instead of within Riek's ecological group two. Patak et al. (1989) later added two additional genera to their study (Parastacoides and Paranephrops) resulting in a phylogeny that differed in the placement of Cherax and Euastacus. Using a goodness of fit test in association with the immunochemical data, Patak et al. (1989) rejected their previous tree as well as the hypothesis of Riek (1972), concluding these were incompatible with their new data set.
Austin (1995) proposed a sister relationship between Cherax and Geocharax based on allozyme data (24 enzymatic loci) and morphological data (55 characters, including most traits previously emphasized by Riek [1969, 1972] and Hobbs ). Treating the morphological data and allozyme data as independent data sets, Austin (1995) obtained support for the clustering of Cherax with Geocharax in both cases. Finally, Crandall et al. (1995) reconstructed phylogenetic relationships for representatives of various Australian genera using nucleotide sequence data from the 16S mitochondrial genome. The resulting tree was statistically incompatible with the hypotheses proposed by Riek and the Patak and Baldwin hypothesis. However, the results were compatible with the Patak et al. (1989) and the Austin (1995) hypotheses. For a summary of these alternative hypotheses see Crandall et al. (1995). Because none of these studies have included all the genera found in Australia (not to mention in the family Parastacidae) the tree shown is Riek's (1969) with the additional southern hemisphere genera included with relationships suggested by Hobbs (1988;1991).
Molecular Biology and Genetics
Statistics of barcoding coverage
Specimens with Sequences:578
Specimens with Barcodes:509
Species With Barcodes:122
Parastacidae is the family of freshwater crayfish found in the southern hemisphere. The family is a classic Gondwana-distributed taxon, with extant members in South America, Madagascar, Australia, New Zealand and New Guinea, and extinct taxa also in Antarctica.
Australasia is particularly rich in crayfish. The small genus Paranephrops is endemic to New Zealand. Two genera, Astacopsis and Parastacoides are endemic to Tasmania, while a further two are found on either side of the Bass Strait – Geocharax and Engaeus. The greatest diversity, however, is found on the Australian mainland. Three genera are endemic and have restricted distributions (Engaewa, Gramastacus and Tenuibranchiurus), while two are more widespread and contain nearly ninety species between them: Euastacus, around the Australian coast from Melbourne to Brisbane, and Cherax across Australia and New Guinea.
The oldest specimens from the family Parastacidae are the Albian fossils of Palaeoechinastacus from Victoria, Australia. The only northern hemisphere representative is also a fossil, Aenigmastacus crandalli from Canada.
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