Currently, between one-third and two-thirds of marine species may be undescribed, and previous estimates of there being well over one million marine species appear highly unlikely. More species than ever before are being described annually by an increasing number of authors. If the current trend continues, most species will be discovered this century.

The freshwater crayfishes are a group of decapod crustaceans that have played a critical role in a diversity of biological studies, from physiology, to ecology, neurobiology, conservation, and evolution. Central to many of these fields of study is the dependence on a robust taxonomic framework for accurate communication relating to species diversity and associated attributes. Despite a huge body of taxonomic work since Linnaeus, there has never been a single, comprehensive taxonomic summary of all the species of crayfish of the world. There has also been an abundance of recent taxonomic work in terms of new species descriptions and taxonomic insights gained from a variety of phylogenetic studies. Here we gather diverse taxonomic and phylogenetic information into a single resource. We develop an updated classification system that includes all the crayfishes worldwide and taxonomic changes to better reflect the current phylogenetic knowledge of the group. We also include all the fossil crayfish taxa for a complete classification of extant and extinct crayfishes. Our classification results in two superfamilies (Astacoidea and Parastacoidea), five families, 38 genera, and 669 species (692 including distinct subspecies). We provide a checklist of all species and include validated taxonomic authorities, type localities, figure references, and synonyms. We also provide arguments for our revised classification. The updated and complete classification aims to provide a robust framework for future studies of the freshwater crayfishes of the world.

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The majority of the almost 1,000 species of Palaemonidae, the most speciose family of caridean shrimp, largely live in symbioses with marine invertebrates of different phyla. These associations range from weak epibiosis to obligatory endosymbiosis and from restricted commensalism to semi-parasitism, with the specialisation to particular hosts likely playing a role in the diversification of this shrimp group. Our study elucidates the evolutionary history of symbiotic palaemonids based on a phylogenetic analysis of 87 species belonging to 43 genera from the Indo-West Pacific and the Atlantic using two nuclear and two mitochondrial markers. A complementary three-marker analysis including taxa from GenBank raises this number to 107 species from 48 genera. Seven larger clades were recovered in the molecular phylogeny; the basal-most one includes mostly free-living shrimp, albeit with a few symbiotic species. Ancestral state reconstruction revealed that free-living forms likely colonised cnidarian hosts initially, and switching between different host phyla occurred multiple times in palaemonid evolutionary history. In some cases this was likely facilitated by the availability of analogous microhabitats in unrelated but morphologically similar host groups. Host switching and adaptations to newly colonised host groups must have played an important role in the evolution of this diverse shrimp group.

Regional scale speciation reveals multiple invasions of freshwater in Palaemoninae (Decapoda).-Zoologica Scripta, 41, 293-306. The generic level, systematic relationship in Palaemoninae was inferred from analyses based on the mitochondrial 16S rDNA and nuclear Histone (H3) genes, primarily focussed on the genera Palaemon and Palaemonetes, as previous morphological and molecular studies indicated potential paraphyly in some genera. Palaemonetes, Exopalaemon, Coutierella and certain Palaemon recover as a strongly supported monophyletic clade, but with the exception of Palaemon concinnus, P. pandaliformis and P. gracilis. Within this clade, six major clades are identified with geographic relationships appearing stronger than generic relationships. The data strongly suggest that Palaemon, Palaemonetes, Exopalaemon and Coutierella are synonymous and that the morphological characters currently used to define these genera require re-evaluation. Freshwater species are not closely related to each other, but instead group with geographically close marine species, suggesting multiple invasions of freshwater by physiologically plastic ancestors rather than a single colonisation event with subsequent speciation.

Freshwater caridean shrimps account for approximately a quarter of all described Caridea, numerically dominated by the Atyidae and Palaemonidae. With the exception of Antarctica, freshwater shrimp are present in all biogeographical regions. However, the Oriental region harbours the majority of species, whilst the Nearctic and western Palaearctic are very species-poor. Many species are important components of subsistence fisheries, whilst the Giant River Prawn forms the basis of an extensive aquaculture industry. A total of 13 species are threatened or endangered, with one species formally extinct.

We present the first global assessment of extinction risk for a major group of freshwater invertebrates, caridean shrimps. The risk of extinction for all 763 species was assessed using the IUCN Red List criteria that include geographic ranges, habitats, ecology and past and present threats. The Indo-Malayan region holds over half of global species diversity, with a peak in Indo-China and southern China. Shrimps primarily inhabit flowing water; however, a significant subterranean component is present, which is more threatened than the surface fauna. Two species are extinct with a further 10 possibly extinct, and almost one third of species are either threatened or Near Threatened (NT). Threats to freshwater shrimps include agricultural and urban pollution impact over two-thirds of threatened and NT species. Invasive species and climate change have the greatest overall impact of all threats (based on combined timing, scope and severity of threats).

Freshwater caridean shrimps account for approximately a quarter of all described Caridea, numerically dominated by the Atyidae and Palaemonidae. With the exception of Antarctica, freshwater shrimp are present in all biogeographical regions. However, the Oriental region harbours the majority of species, whilst the Nearctic and western Palaearctic are very species-poor. Many species are important components of subsistence fisheries, whilst the Giant River Prawn forms the basis of an extensive aquaculture industry. A total of 13 species are threatened or endangered, with one species formally extinct.