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Phylogenetic reconstruction, divergence time estimations and ancestral range estimation were undertaken for 66% of the Afrotropical freshwater crab fauna (Potamonautidae) based on four partial DNA loci (12S rRNA, 16S rRNA, cytochrome oxidase one [COI], and histone 3). The present study represents the most comprehensive taxonomic sampling of any freshwater crab family globally, and explores the impact of paleodrainage interconnectivity on cladogenesis among freshwater crabs. Phylogenetic analyses of the total evidence data using maximum-likelihood (ML), maximum parsimony (MP), and Bayesian inference (BI) produced a robust statistically well-supported tree topology that reaffirmed the monophyly of the Afrotropical freshwater crab fauna. The estimated divergence times suggest that the Afrotropical Potamonautidae diverged during the Eocene. Cladogenesis within and among several genera occurred predominantly during the Miocene, which was associated with major tectonic and climatic ameliorations throughout the region. Paleodrainage connectivity was observed with specimens from the Nilo-Sudan and East African coast proving to be sister to specimens from the Upper Guinea Forests in West Africa. In addition, we observed strong sister taxon affinity between specimens from East Africa and the Congo basin, including specimens from Lake Tanganyika, while the southern African fauna was retrieved as sister to the Angolan taxa. Within the East African clade we observed two independent transoceanic dispersal events, one to the Seychelles Archipelago and a second to Madagascar, while we observe a single transoceanic dispersal event from West Africa to Sao Tomé. The ancestral area estimation suggested a West African/East African ancestral range for the family with multiple dispersal events between southern Africa and East Africa, and between East Africa and Central Africa The taxonomic implications of our results are discussed in light of the widespread paraphyly evident among a number of genera.

An assessment of the global freshwater crab diversity is presented. A total of 1,476 species in 14 families are currently known from all zoogeographical regions (except Antarctica), including 1,306 species in eight exclusively freshwater families (Pseudothelphusidae, Trichodactylidae, Potamonautidae, Deckeniidae, Platythelphusidae, Potamidae, Gecarcinucidae and Parathelphusidae). Estimates of true freshwater crab diversity including likely numbers of undescribed taxa suggest that the field remains largely in a “discovery” phase. Main ideas on the origins, diversification, and phylogeny of true freshwater crabs are briefly discussed. The economic importance of freshwater crabs is also highlighted.

A new species of freshwater crab, Potamonautes amathole sp. nov. , is described from the Winterberg-Amathole mountain range in the Eastern Cape Province, South Africa. Morphologically, P. amathole Peer & Gouws, sp. nov. most closely resembles P. tuerkayi but can be distinguished by key morphological characters including the variation in the shape of the subterminal segment of gonopod 2 between both species. Genetically, P. amathole Peer & Gouws, sp. nov. is placed within the clade of small-bodied, mountain-dwelling crabs including P. parvispina , P. parvicorpus , P. brincki , P. tuerkayi , P. baziya , and P. depressus . The new species is found in slow-moving mountain streams and pools at high altitudes. The continued discovery and description of new freshwater crab species reinforces the need for ongoing research, especially in under-sampled regions.

Louisea Cumberlidge, 1994 (Crustacea, Brachyura, Potamonautidae) currently includes four endemic Cameroonian freshwater crab species whose phylogenetic relationships were previously unresolved. In the present study, phylogenetic analyses are carried out involving three mtDNA loci (COI, 12S rRNA, and 16S rRNA). The COI locus revealed divergence times of 5.6 million years ago (myr) for when L. balssi (Bott, 1959) diverged from L. edeaensis (Bott, 1969); 4.1 myr for when L. edeaensis diverged from L. yabassi Mvogo Ndongo, von Rintelen & Cumberlidge, 2019; and 2.48 myr for when the later species diverged from L. nkongsamba Mvogo Ndongo, von Rintelen & Cumberlidge, 2019. Three genetic lineages were found within L. nkongsamba that are supported by uncorrected p -distances and the haplotype network. Morphological variation in some taxonomically important characters was found within both L. nkongsamba and L. yabassi . No correlation, however, was found between the morphotypes within these species and the uncovered genetic lineages. Recognition of species boundaries and of subpopulations of species will prove valuable when making informed conservation decisions as part of the development of species action plans for these rare and threatened freshwater crabs.

Four new species of freshwater crab are described from material collected in northern and southwestern Cameroon and assigned to Sudanonautes Bott, 1955. Sudanonautes cameroonensis sp. n., S. eyimba sp. n., S. ngaoundere sp. n. and S. nkam sp. n., are distinguished by characters of the carapace, thoracic sternum, chelipeds, mandibles, adult male gonopods, and in addition by genetic analyses using the mitochondrial CO1 and 16S rRNA genes. Diagnoses, illustrations, and a phylogenetic tree based on mtDNA sequences are provided, as well as a discussion of the threats and conservation of all species.

A new species of freshwater crab of the genus Potamonemus Cumberlidge & Clark, 1992 is described from Mount Manengouba Reserve and Bakossi National Park in the tropical rainforests of southwestern Cameroon, Central Africa. Potamonemus man sp. nov. is recognized by characters of the carapace and chelipeds. In addition, a phylogenetic analysis based on partial sequences of three mitochondrial DNA genes (COI, 12S rRNA, and 16S rRNA) that included representatives of all other freshwater crab genera found in Cameroon recovered each of the new species as a distinct lineage. A diagnosis and illustrations of the new species are provided, and it is compared to the other species of Potamonemus . Brief notes are provided on the ecology of the new species and the two other species of Potamonemus . An identification key to the species of Potamonemus is provided. The conservation status of the genus is discussed.

The taxonomy of the freshwater crab genus Louisea Cumberlidge, 1994, is reviewed based on type material and newly obtained specimens from three different localities in southwestern Cameroon. The genus is endemic to Cameroon and previously included two species: L. edeaensis (Bott, 1969) (type species) from Lake Ossa wetland complex (altitudes below 400 m asl) and L. balssi (Bott, 1959) from Kumba and Mt. Manengouba (altitudes above 1300 m asl). Here two new species of Louisea are described based on morphological and/or genetic data: L. nkongsamba sp. nov. from the Nlonako Ecological Reserve (1000–1400 m asl) in the sub-montane zone and L. yabassi sp. nov . from Yabassi in the lowlands. A redescription and amended diagnostic features of L. edeaensis and L. balssi are provided, and the genus diagnosis is updated to accommodate all four species. An identification key is also provided for the species of Louisea . A tree of phylogenetic relationships based on three mtDNA loci (COI, 12S rRNA, and 16S rRNA) supports the taxonomic revision, and indicates speciation of Louisea species along an altitudinal gradient, but further phylogenetic analyses are needed to understand whether this can lend support to the hypothesis that there is a montane centre of speciation along the Cameroon Volcanic Line. The phylogenetic tree also shows that Buea Cumberlidge, Mvogo Ndongo, Clark & Daniels, 2019 and Potamonemus Cumberlidge & Clark, 1992 are sister genera that may be derived from the Louisea lineage.

Adaptations to a terrestrial lifestyle occurred convergently multiple times during the evolution of the arthropods. This holds also true for the “true crabs” (Brachyura), a taxon that includes several lineages that invaded land independently. During an evolutionary transition from sea to land, animals have to develop a variety of physiological and anatomical adaptations to a terrestrial life style related to respiration, reproduction, development, circulation, ion and water balance. In addition, sensory systems that function in air instead of in water are essential for an animal’s life on land. Besides vision and mechanosensory systems, on land, the chemical senses have to be modified substantially in comparison to their function in water. Among arthropods, insects are the most successful ones to evolve aerial olfaction. Various aspects of terrestrial adaptation have also been analyzed in those crustacean lineages that evolved terrestrial representatives including the taxa Anomala, Brachyura, Amphipoda, and Isopoda. We are interested in how the chemical senses of terrestrial crustaceans are modified to function in air. Therefore, in this study, we analyzed the brains and more specifically the structure of the olfactory system of representatives of brachyuran crabs that display different degrees of terrestriality, from exclusively marine to mainly terrestrial. The methods we used included immunohistochemistry, detection of autofluorescence- and confocal microscopy, as well as three-dimensional reconstruction and morphometry. Our comparative approach shows that both the peripheral and central olfactory pathways are reduced in terrestrial members in comparison to their marine relatives, suggesting a limited function of their olfactory system on land. We conclude that for arthropod lineages that invaded land, evolving aerial olfaction is no trivial task.

The need for highly-variable, nuclear microsatellite markers to accurately determine population genetic structure and infer patterns of gene flow and dispersal in true freshwater crabs of the genus Potamonautes MacLeay, 1838 (Potamonautidae) was raised more than a decade ago. The present study uses a shotgun genomic approach, next-generation sequencing and a bioinformatics pipeline designed for isolating microsatellites from Illumina sequence read data to isolate di- and tetra-nucleotide repeat microsatellites for Potamonautes danielsi Peer, Gouws, Lazo-Wasem, Perissinotto & Miranda, 2017 from data produced by a fraction of a MiSeq run. Twelve loci were initially identified, with reproducible amplification of eight loci in the target species. Compiled in two multiplex reactions, all eight loci were polymorphic with between three and 15 alleles. Evaluated according to PIC, three loci were considered to be highly informative and four as reasonably informative. Cross-amplification success was evaluated by screening loci for three species (P. lividus Gouws, Stewart & Reavell, 2001, P. principe Cumberlidge, Clark & Baillie, 2002 and P. sidneyi (Rathbun, 1904)) representing varying degrees of phylogenetic relatedness to P. danielsi. Cross-amplification attenuated along with relatedness, with seven loci being successfully amplified P. lividus and P. sidneyi, and four in P. principe. The number of polymorphic loci was further reduced and, for P. sidneyi at least, individual amplification success was low. Nonetheless, the present study does present a microsatellite panel that can be applied to population genetic studies of the widespread P. danielsi and has some potential for closely-related species. This is only the third microsatellite panel to be developed for the true freshwater crabs.

Evolutionary relationships amongst three species of freshwater crabs, Liberonautes latidactylus (De Man, 1903), L. nimba Cumberlidge, 1999, and L. rubigimanus Cumberlidge and Sachs, 1989, were examined using DNA sequence data of the mitochondrial cytochrome oxidase subunit I (COI) locus. The latter three species are listed in the IUCN Red List for 2008 as least concerned, vulnerable, and endangered, respectively. Specimens of the three species were collected in Liberia and neighbouring Guinea, West Africa. Phylogenetic results derived from maximum parsimony, maximum likelihood, and Bayesian inference revealed the monophyly of all three species. Moderate genetic variation was observed within L. latidactylus. Within the narrow endemic, montane species, L. nimba shallow divergence was observed, whereas marked genetic divergence was observed within L. rubigimanus. Three statistically well-supported clades were observed within the latter taxon, two of these clades were sympatric at Simandou, Liberia (clades A and B), and characterised by a 10% uncorrected sequence divergence for the COI locus, whereas the divergence between the latter two clades and the larger L. rubigimanus clade was 8%. Haplotype networks corroborate the absence of maternal gene flow amongst the three L. rubigimanus clades suggesting possible reproductive isolation and the presence of two novel species. Our results suggest that Liberonautes harbours undescribed, narrowly distributed species. The results are discussed in a conservation framework for the three Liberonautes species.