Redescription of Euastacus clydensis Riek, 1969 (Crustacea: Parastacidae), a valid species of spiny crayfish from southern New South Wales, Australia.

The Giant Sydney Crayfish (Euastacus spinifer (Heller, 1865)) was thought to have a wide range in New South Wales, Australia, spanning some 600 km north-south. A recent extensive molecular phylogenetic and population genomic analysis of E. spinifer across its geographical range revealed strong population structure corresponding to several major geographically correlated clades, the southernmost clade being the most genetically divergent and clearly a separate species. This southern clade corresponds to the junior synonym E. clydensis Riek, 1969 and is sister to the clade comprising the remaining populations of E. spinifer and Euastacus vesper. We formally remove E. clydensis from the synonymy of E. spinifer, increasing the recognised number of species of Euastacus to 54. Euastacus clydensis is redescribed based on type and other material, and is distinguished from E. spinifer by differences in abdominal spination and the form of the antennal scaphocerite. Euastacus clydensis has a restricted southern New South Wales range in the Shoalhaven and Jervis Bay-Clyde River catchments, from Moss Vale south to the vicinity of Clyde Mountain; much of the known range of E. clydensis was burnt in the 2019-2020 eastern Australian megafires.

Cherax latimanus sp. nov., a new burrow-dwelling freshwater crayfish (Decapoda, Parastacidae) from the mid-Murray River catchment, Australia.

A new species of freshwater crayfish in the southern hemisphere family Parastacidae is described from the Murray Darling Basin (MDB), eastern Australia. The Swamp Yabby, Cherax latimanus sp. nov., is found in the mid-Murray River area of the states of New South Wales and Victoria and is only the third species of Cherax found naturally occurring in the MDB. It is morphologically distinguished from all other species of Cherax by the presence of marginal mesial dactylar basal spines and extensive ventral propodal setation. It is found in sympatry with the widespread but morphologically similar Common Yabby, Cherax destructor Clark, 1936, but can be distinguished by a suite of morphometric and meristic characters that include a broad rostrum lacking an apical spine, very broad chelae with deep punctations on the lateral propodal edge and ventral propodal setation, two prominent dactylar teeth, one mesial carpal spine, dorsal meral spines present, no setae on carpal mesial margin, cervical spines absent or tiny, and by genetic data. Cherax latimanus is further diagnosed by its distinctive biology: it is not found in permanent aquatic habitats such as streams or billabongs, spending the majority of its time in extensive, terrestrial, burrow networks containing some water, in ephemerally wet habitats such as drainage lines, roadside drains, depressions, swamps and cleared areas of pasture in lowland to foothill areas. It is occasionally found in stream habitats but only during large flood events when burrow systems are inundated.

Euastacus vesper sp. nov., a new giant spiny crayfish (Crustacea, Decapoda, Parastacidae) from the Great Dividing Range, New South Wales, Australia.

Euastacus vesper sp. nov., is described from the upper Cudgegong River, Coricudgy State Forest, New South Wales, Australia. The new species occurs in the western drainage of the Great Dividing Range, and is most closely related to E. spinifer (Heller, 1865), which occurs on the eastern side of the range. Euastacus vesper differs from E. spinifer by its considerably smaller maximum size (OCL 67.9 mm versus 116.7 mm), greater degree of thoracic spination loosely arrayed in three instead of two rows and absence of the antennular basipodite and coxopodite spines. Observations on burrowing, ecological preferences and biology are presented.

The eastern swamp crayfish Gramastacus lacus sp. n. (Decapoda, Parastacidae) a new species of freshwater crayfish from coastal New South Wales, Australia.

Gramastacus lacus sp. n., is described from coastal lowlands of the Central and Mid North Coast regions of New South Wales, Australia. Gramastacus lacus has a restricted distribution in ephemeral habitats, being dependent on regular natural flooding and drying cycles, and burrows for survival during temporary dry cycles. Documented are population distributions in lowland habitats (3-48 m, a.s.l.) from Wamberal Lagoon, north along the coastal strip to Wallis Lake. The species is small, reaching a maximum weight of 7 grams and 21.3 mm OCL, and distinguished by a large male genital papilla, large raised post orbital ridges, laterally compressed carapace and elongated chelae.

Euastacus morgani sp. n., a new spiny crayfish (Crustacea, Decapoda, Parastacidae) from the highland rainforests of eastern New South Wales, Australia.

Euastacus morgani sp. n., is described from a highland, rainforest site in Bindarri National Park, in eastern New South Wales, Australia. Euastacus morgani is found living sympatrically with two more common species, Euastacus dangadi Morgan, 1997 and Euastacus neohirsutus Riek, 1956. Systematically, the species belongs in the 'simplex' complex of the genus that includes Euastacus simplex Riek, 1956, Euastacus clarkae Morgan, 1997, Euastacus maccai McCormack and Coughran 2008 and E. morgani. This new species differs from its nearest congenor, Euastacus simplex, in having three mesial carpal spines. A key to the 'simplex' complex is presented.