Freshwater Crab Research Articles

Digitization of the Data on Indian Freshwater Crabs: 1 Travancoriana Schirnerae Bott, 1969 (Decapoda: Gecarcinucidae)

This resent research article is on the digitized form of valuable data on freshwater crab, Travancoriana schirnerae Bott, 1969. The data acquired from various sources, such as, internet articles, published research articles and databases about the species has been organized in the form of a web portal open for access for a wider audience. The data collected are categorized into 15 user friendly heads such as, Species name, Anatomy, Life Cycle, Moulting, Spawning, Diseases, Fossils, Fisheries and Industries, Nutritive value, Internet links, Books and resources, Barcoding, General Biology, References of resources and General Aspects, under the title named resources. Digitization will ensure to provide background information to all those are interested to continue further in research in this area and this forms the major objective of the paper.

Mitogenome phylogeny reveals Indochina Peninsula origin and spatiotemporal diversification of freshwater crabs (Potamidae: Potamiscinae) in China.

The Asian potamid subfamily Potamiscinae is the most species-rich group of primary freshwater crabs in the world, and a large number of these (318 species in 52 genera) are found in China where they exhibit a remarkably high rate of endemism. However, the evolutionary history and phylogenetic relationships of this subfamily is still poorly understood and the hypothesis that the Chinese potamids originated in the Indochina Peninsula has yet to be tested using a modern phylogeographic reconstruction and molecular dating methods. Here we analyze the phylogenetic relationships and biogeographic history of the Chinese potamiscines based on whole mitogenomes of 72 species of Asian freshwater crabs representing 65% of the potamiscine genera found in China, including new mitogenome sequences for 57 species. The mitogenomic phylogeny generated four separate clades: Southwest China (SWC), Indochina-Southwest China (ISWC), Central China (CC), and South China-adjacent Islands (SCI). Our results suggest that the Chinese potamiscine fauna most likely originated in Indochina during the Eocene. The establishment of the East Asian monsoon during the Eocene/Oligocene resulted in major climate changes that coincide with the local diversification of the CC and SCI clades. In addition, diversification of two other clades (ISWC and SWC) may have been driven by past large scale environmental changes taking place at that time such as increased local precipitation and expanding freshwater habitats associated with the uplifting of the Hengduan Mountains. In addition, our phylogenies did not support monophyly for six currently recognized potamiscine genera, highlighting the need for further taxonomic revisions of this fauna. The broad taxonomic sampling and well-supported molecular phylogenies used here allow for the updating of our understanding of the evolutionary origins and diversification of the potamiscine freshwater crabs in China.

Description of a new genus and new species of freshwater crab (Brachyura: Potamoidea) from southern Vietnam

Description of a new genus and new species of freshwater crab (Brachyura: Potamoidea) from southern Vietnam

Short communication: Effects of acute copper exposure on ionic regulation of the freshwater crab Aegla castro

Aeglids are unique freshwater decapods whose habitats are being impacted by metallic compounds, such as copper (Cu). Thus, we investigated the effects of acute Cu exposure on ionic regulation of Aegla castro. For this, male specimens in intermolt were collected from a reference stream and acclimated for 5 days in laboratory. After which, crabs were exposed to 11 μg L−1 Cu (Cu11) or only to water (CTR) for 24 h. Hemolymph samples were withdrawn for the determination of Na+, K+, Ca2+, and Mg2+ concentrations and the posterior gills removed for the analysis of Na+/K+-ATPase, Ca2+-ATPase, H+-ATPase, and carbonic anhydrase (CA) activities. Increased Ca2+ and Mg2+ hemolymph concentrations were observed in animals from Cu11, when compared with CTR group. In addition, decreased activity of CA was observed in animals exposed to Cu. In the current study, alterations in Ca2+ and Mg2+concentrations probably indicate that animals activated exoskeleton reabsorption mechanisms, characteristic of the premolt. Therefore, increased Ca2+ and Mg2+ concentrations in hemolymph may indicate that a biochemical signal associated with the molting cycle was triggered by Cu exposure. Despite the known harmful effects of Cu on osmoregulatory enzymes, here we observed decreased activity only in CA. However, decreased activity of CA could trigger both acid-base imbalance and ionic disruption, since CA provides H+ and HCO3− for intracellular pH maintenance, and underpins Na+ and Cl− for ionic regulation. Therefore, understanding how aeglids respond to metal contamination in laboratory conditions is crucial to assess their potential as an alternative biological model for aquatic ecotoxicology.

Detoxification and recovery after cadmium exposure in the freshwater crab Sinopotamon henanense.

Cadmium (Cd) is a common pollutant in the aquatic environment, which puts the health and safety of aquatic organisms and humans at risk. In the present study, the freshwater crab Sinopotamon henanense was exposed to Cd (0, 50, 100, and 500 μg·L-1) for 14 d (0-14th d), followed by 21 d (14-35th d) of depuration. The changes in Cd bioaccumulation, microstructure, biomacromolecules (polysaccharides, neutral lipids, DNA and total proteins), and biochemical parameters (SOD, CAT, GR, TrxR, MDA and AChE) in the gills and hepatopancreas were tested. The injured microstructure, activated antioxidant system, increased MDA, and inhibited AChE of the gills and hepatopancreas responded with progressive bioaccumulation of Cd. Meanwhile, the polysaccharides and neutral lipids in the hepatopancreas reduced and DNA synthesis enhanced. During depuration, more than 58.80 ± 8.53% and 13.84 ± 12.11% of Cd was excreted from the gills and hepatopancreas, respectively. Recovery of microstructure and biomacromolecules as well as alleviated oxidative damage and neurotoxicity were also found in these two organs. Additionally, based on PCA, Ihis, GR and MDA were identified as the optimal biomarkers indicating the health status of crabs. In conclusion, S. henanense could resist Cd stress through antioxidant defence and self-detoxification.

Oliverio O. Segura, MD (1933-2021) Through A Son’s Eyes – A Tribute to Dad

Oliverio O. Segura, MD (1933-2021) Through A Son’s Eyes – A Tribute to Dad

Discovery of two new populations of the rare endemic freshwater crab Louisea yabassi Mvogo Ndongo, von Rintelen & Cumberlidge, 2019 (Brachyura: Potamonautidae) from the Ebo Forest near Yabassi in Cameroon, Central Africa, with recommendations for conservation action

The endemic freshwater crab, Louisea yabassi Mvogo Ndongo, von Rintelen & Cumberlidge, 2019, is currently only known from three populations in the biodiversity-rich rainforests of southwestern Cameroon. The first record of L. yabassi dates back to 1908 from Yabassi, while the other two populations were discovered in December 2019 and March 2020 from the Ebo Forest near Yabassi. These specimens were initially identified as L. edeaensis (Bott, 1969), but were subsequently assigned to L. yabassi. The newly-discovered populations of L. yabassi provided important data on its habitat, population structure and geographical distribution, all critical knowledge for conservation measures. Reported here are the anthropogenic threats to L. yabassi and its rainforest habitat, which include forest destruction, agricultural encroachment, water pollution and firewood collection. This information is inherently useful in the assessment of the extinction risk of L. yabassi and highlights the importance of implementing strategies for preserving primary rainforest and its associated aquatic habitats in Central Africa.

Baseline growth of the Trinidad freshwater crab Poppiana dentata () under laboratory conditions.

Poppiana dentata (Randall, 1840) is widely distributed throughout riverine habitats in Trinidad. However, there is a scarcity of information on the biology of this species. This study provides the first baseline examination that describes growth aspects for P. dentata. Juvenile crabs were obtained from berried females collected in northwest Trinidad. Carapace width (CW), length (CL), moult incident, intermoult period and qualitative aspects were recorded for crabs (N = 23) over 9 months. CW, CL and intermoult period were used to derive percentage size increment, specific growth rate (SGR) and size at structural maturity for both sexes. Growth curves and logistic equations were also generated for each sex. Hatched crabs (< 5 mm CW) underwent rapid hardening after their first moult, indicating a fast turnover of moult cycles. SGR and CW percent increment were also the highest for this initial moult (P < 0.05). CW, CL, intermoult period, size increment and SGR did not differ between sexes (P > 0.05), with logistic equations expressed as CW = 32.81 (1+exp (1.481 ̵ 0.031t))-1 for males and CW = 34.07 (1+exp (1.516 ̵ 0.027t))-1 for females. Yet, breakpoint analyses indicated dissimilar sizes for structural maturity (male: 28.40 mm CW; female: 16.84 mm CW). These patterns reflect a shorter life span for this species in comparison to what has been reported for other trichodactylid relatives. This can have implications for P. dentata populations residing in anthropogenically disturbed habitats; thus, highlighting the need for conservation strategies to ensure preservation of native wild stock.

Natural diet of the endemic freshwater crab Aegla castro Schmitt, 1942 (Decapoda: Anomura: Aeglidae)

Abstract We characterized the natural diet and feeding dynamics of Aegla castroSchmitt, 1942 (Aeglidae), an endemic freshwater crab. Research was undertaken on the trophic spectrum of the species by analyzing the stomach contents of individuals collected in a stream in southeastern Brazil, and evaluating the diet through the index of relative importance (IRI). Seasonal and circadian variations in diet composition were analyzed, and the feeding dynamics investigated through repletion index (RI) analysis. We analyzed a total of 240 stomachs and identified 20 main food categories of the diet, which were studied throughout the seasons. Aegla castro maintained a constant RI throughout the year, with a peak of food activity between midnight (00) and 0600. The species was characterized as an omnivorous generalist and opportunist. The high overlay in the diet composition of adults of both sexes and juveniles indicates that they share the same food resources, even though they seem to exploit them in different quantities and frequencies. Future research should focus on the species of Aegla whose diets have not yet been described, and use available data to inform trophic network analyses and models.

Unravelling the Potamonautes lirrangensis (Rathbun, 1904) species complex (Potamoidea: Potamonautidae), with the description of two new species

The taxonomic status of the widely distributed freshwater crab Potamonautes lirrangensis (Rathbun, 1904) sensu lato is revised because morphological and molecular evidence indicates that this taxon is a complex comprising more than one species. Four taxa are now recognized: Potamonautes lirrangensis (Rathbun, 1904) s. str. and P. kisangani sp. nov. from the Middle Congo River in Central Africa, P. amosae sp. nov. from the drainages of Lakes Kivu and Tanganyika, and P. orbitospinus (Cunnington, 1907) from Lake Malawi which had been previously synonymised with P. lirrangensis s. lat. Diagnoses, illustrations and distribution maps are provided for each of these taxa and they are compared to similar species from Central and Southern Africa.

Antiproliferative effects of fresh water crab hemolymph and meat extract on breast cancer cell line

Background and aims: Despite the advances in drugs, side effects of chemotherapy drugs continue to exist. Therefore, more attention has been paid to the compounds derived from medicinal herbs and aquatic organisms. This study aimed to investigate the effect of freshwater crab hemolymph and meat extract on breast cancer (BC) cell line (4T1). Methods: After isolation of freshwater crab hemolymph and meat extract, protein concentration and total antioxidant capacity were analyzed by bicinchoninic acid (BCA) and cupric reducing antioxidant capacity (CUPRAC) methods. The 4T1 cells and bone marrow mesenchymal stem cells (BMSCs) were treated with crab hemolymph (1, 2, 10 mg/mL) and meat extract (0.1, 0.2 and 1 mg/mL), and cell survival was analyzed using 3-(4, 5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay (MTT) at 48 and 72 hours. Nitric oxide (NO) secretion was measured by Griess method. Data were analyzed using one-way analysis of variance (ANOVA). Results: Protein concentration of 23.25 mg/mL was shown in crab hemolymph, and 2.3 mg/mL in meat extract. Total antioxidant capacity was reported as 1.036 µM/mL and 1.104 µM/mL in crab hemolymph and meat extract, respectively. Cell survival in the 4T1 cells was decreased in a dose- and time-dependent manner (P≤0.001). NO secretion of 4T1 cells was decreased after treatment with different concentrations of crab hemolymph and meat extract at 48 and 72 hours. Cellular growth was observed in BMSCs after treatment with different concentrations of crab hemolymph and meat extract at 48 and 72 hours. Conclusion: Since crab hemolymph and meat extract have protein and antioxidant activities, they can have anti-cancer effects on 4T1 cells.

Analysis of the misdiagnosis of 8 adult cases of paragonimiasis with lung masses as the main manifestation in Xishuangbanna, Yunnan

ObjectiveTo summarize the clinical characteristics of adult cases of paragonimiasis with lung masses as the main manifestation in Xishuangbanna, Yunnan Province, analyze the causes of misdiagnosis, and improve the levels of clinical diagnosis and treatment.MethodWe conducted a retrospective analysis of the clinical data and diagnosis and treatment of 8 adult cases of paragonimiasis with lung masses as the main manifestation that were diagnosed in the Oncology Department of People’s hospital of Xishuangbanna Dai Autonomous Prefecture from July 2014 to July 2019.ResultAll 8 patients were from epidemic paragonimiasis areas and had a confirmed history of consuming uncooked freshwater crabs. The clinical manifestations were mainly fever, dry cough, and chest pain. The disease durations were long, and peripheral blood eosinophil counts were elevated. The cases had been misdiagnosed as pneumonia or pulmonary tuberculosis. After years of anti-inflammatory or anti-tuberculosis treatment, the symptoms had not improved significantly. Patients eventually sought treatment from the oncology department for hemoptysis. Chest computed tomography showed patchy consolidation in the lungs, with nodules, lung masses, and enlarged mediastinal lymph nodes.ConclusionParagonimiasis is a food-borne parasitic disease. Early clinical manifestations and auxiliary examination results are nonspecific. The parasite most often invades the lungs, and the resulting disease is often misdiagnosed as pneumonia, pulmonary tuberculosis, or lung cancer (Acta Trop 199: 05074, 2019). To avoid misdiagnosis, clinicians should inquire, in detail, about residence history and history of unclean food and exposure to infected water and make an early diagnosis based on the inquired information and imaging examination results. For patients who have been diagnosed with pneumonia or pulmonary tuberculosis and whose symptoms do not improve significantly after anti-inflammatory or anti-tuberculosis treatments, their epidemiological history should be traced to further conduct differential diagnosis and avoid misdiagnosis.

Disentangling the Sudanonautes granulatus (Balss, 1929) species complex (Potamoidea: Potamonautidae), with the description of two new freshwater crabs from Nigeria and Côte d'Ivoire, West Africa.

The taxonomic status of the widely distributed West and Central African freshwater crab Sudanonautes granulatus (Balss, 1929) sensu lato is revised in the light of improved morphological evidence which indicates that this taxon is a complex comprising at least 4 species: Sudanonautes granulatus (Balss, 1929) sensu stricto from Togo, S. koudougou n. sp. from Côte d'Ivoire, S. umaji n. sp. from Nigeria, and S. tiko from Cameroon, Nigeria, and Bioko. Diagnoses, illustrations and distribution maps are provided for these species and they are compared with congeners from West and Central Africa.

Effects of Physicochemical Variables of Superficial Waters on the Abundance of the North African Freshwater Crab Potamon algeriense (Bott, 1967).

The large number of pollutants discharged into the aquatic environment may influence the physicochemical and biological qualities of the aquatic ecosystem. This study discloses the global quality of the surface waters and the effect of physicochemical variables on the abundance of the African freshwater crab Potamon algeriense inhabiting Zegzel watercourse, a mountain stream in the northeast of Morocco. Physicochemical variables including streamflow, water temperature, pH, dissolved oxygen, suspended matter, chloride, calcium, magnesium, ammonia, nitrite, nitrate, orthophosphate, and organic matter were evaluated monthly for one year (October 2017-September 2018). The evaluation of the physicochemical quality showed that the waters of all the stations studied are between the excellent and good quality classes concerning all the physicochemical variables and highlights also two variations with a tendency towards degradation, one spatial from upstream to downstream and the other seasonal from the wet to the dry period. The abundance of crabs was recorded to exhibit a positive correlation with dissolved oxygen, calcium (N = 44) (p < 0.01), and magnesium. However, a negative correlation has been noticed for streamflow (N = 1) (p < 0.01), water temperature, pH, suspended matter, chloride, ammonia, nitrite, nitrate, orthophosphate, and organic matter. The results obtained reveal that besides the biotic variables, the distribution of P. algeriense also depends on these specific environmental variables.

Entangled Aeglidae (Decapoda, Anomura): Additional evidence for cryptic species

AbstractCryptic species are a major challenge for morphologically based species identification. Molecular approaches to species delimitation can be a valuable tool to provide preliminary taxonomic hypotheses and significantly complements morphological taxonomy. In South America, the freshwater crabs of the genus Aegla have sparked much interest as they are key species in the often‐endangered freshwater ecosystems and themselves are often considered endangered species. Morphological similarity among Aegla species is not always positively correlated with genetic relatedness and growing evidence suggests that several putative single taxa are actually assemblages of cryptic species. We coupled broad geographically sampling (Argentina, Brazil and Uruguay) with multilocus (COI, 16S and ANT) phylogenies to investigate the diversity of Aegla uruguayana. Our species delimitation analyses suggested that 19 aeglid populations form a well‐supported clade, although individuals from 10 populations possibly represent a complex of cryptic species. The significant amount of cryptic diversity found in aeglids seem to rely on several factors, including habitat fragmentation, life history features, morphological stasis, convergent evolution and recent divergence. The search for new diagnostic characters and the description of the cryptic species that remain unnamed will probably be the next challenge for this unique group of crustaceans.

Invasive crayfish outperform Potamonautid crabs at higher temperatures

Abstract Data on ecological impacts of freshwater crayfish invasions in Africa are scarce but invasion history suggests the likelihood of negative implications for biodiversity. To evaluate the potential for ecological impacts we describe the consumer‐resource dynamics of two established crayfish species (Cherax quadricarinatus and Procambarus clarkii) in comparison with the native trophic analogue, the freshwater crab Potamonautes perlatus preying upon Clarias gariepinus fry using comparative functional responses (FRs) and FR ratio (FRR). Experiments were conducted under dark and light conditions as well as low (19°C) and high (28°C) temperature treatments. All three species exhibited potentially population destabilising Type II (hyperbolic) FRs towards prey, which was significantly higher in the dark than in the light. At low temperatures, P. perlatus exhibited the highest maximum feeding estimate although the FR curve was not significantly different from C. quadricarinatus at the highest prey densities. Both crayfish species had higher attack rates at both temperatures and consumed significantly more prey at the high temperature than P. perlatus. The FRR of both crayfish species at the high temperature treatment was higher than that of P. perlatus due to high attack rate and low handling parameters. At 19°C, P. perlatus had a higher or negligible relative FR magnitude compared to P. clarkii and C. quadricarinatus respectively, which suggests some degree of biotic resistance at this temperature; however, this resistance is decreased at 28°C. Cherax quadricarinatus consistently had disruptive FR parameters across both temperatures. Findings from this study represent an important step towards understanding the impacts of crayfish in Africa for public authorities and environmental managers. The two invasive crayfish species have the potential to exert greater per capita impacts on benthic prey communities in invaded systems as shown by their high FRs and FRRs. Furthermore, C. quadricarinatus is an emerging invader globally and our results provide evidence of potential for negative ecological impact regardless of thermal conditions. African countries and their respective environmental managers should therefore maximise efforts to prevent the introduction and spread of these invaders to conserve native biodiversity.

Regional climates shape the biogeographic history of a broadly distributed freshwater crab species complex

AbstractAimThe evolutionary importance of paleoclimate regimes has been noted in biogeographic studies. However, little is known about how paleoclimate differences shaped the biogeographic pattern and diversification history of the freshwater fauna in important zoogeographical boundary regions. Here, we aim to investigate how past regional climatic differences have shaped the biogeographic history of the inland aquatic fauna in China using an endemic freshwater crab species complex found on both sides of the Qinling Mountains–Huaihe River Line (QHL), a critical ecological boundary in eastern China, as a model system.LocationEastern China, the Qinling Mountains–Huaihe River Line.TaxonThe Sinopotamon yangtsekiense species complex.MethodsA total of 482 individuals of Sinopotamon yangtsekiense sensu lato were collected from 34 localities throughout its entire distributional range. The phylogeographic analyses of population structure, morphological and genetic variations, and demographic dynamics were made based on multiple mtDNA and nuDNA loci and on morphological traits. Fine‐tuned ecological niche modeling was used to reconstruct the location of climatically suitable areas that existed during the Last Glacial Maximum.ResultsThe divergence of two freshwater crab lineages across the QHL correlated with significant past variations in monsoon intensity and with the location of multiple refuges. The divergence time was broadly consistent with the timing of the critical paleoclimate transition event in the mid‐Pleistocene (95% HPD, 0.48–1.06 Ma). Each freshwater crab lineage has evolved distinct male genital traits associated with their isolation in areas with different precipitation rates and temperatures in the past. The patterns of crab distribution observed today reflect past contractions of the two lineages in response to glacial and interglacial cycles during the Pleistocene, followed by their subsequent rapid expansion after the Last Glacial Maximum (~15 kya).Main conclusionsPopulations of the widespread species Sinopotamon yangtsekiense s.l. experienced a deep division in the past that led to the phylogeographical isolation observed today. The two main drivers of genetic isolation in this taxon were (a) differences in the intensity of the monsoons on each side of the QHL boundary during the mid‐Pleistocene, and (b) isolation of different populations of S. yangtsekiense s.l. in a number of separate refuges during the LGM.

Comparative responses of Sinopotamon henanense to acute and sub-chronic Cd exposure.

Studies on the freshwater crab Sinopotamon henanense have shown that acute and sub-chronic Cd2+ exposure induced differential alterations in the respiratory physiology and gill morphology. To elucidate Cd2+ toxicity under these two exposure conditions, crabs were acutely exposed to 7.14, 14.28, and 28.55 mg/L Cd2+ for 96 h and sub-chronically exposed to 0.71, 1.43, and 2.86 mg/L Cd2+ for 3 weeks. The Cd2+ accumulation, total metallothionein (MT), superoxide dismutase, and malondialdehyde (MDA) contents in the gill tissues were detected. Moreover, the glucose-6-phosphate dehydrogenase (G6PDH) activity, NADPH content, reduced glutathione (GSH), oxidized glutathione (GSSG), and GSH/GSSG ratio in the hepatopancreas were determined. The morphology of the X-organ-sinus gland complex was also observed. The results showed that sub-chronical Cd2+ exposure induced lower MT content and higher MDA level in the gills than in the acute exposure. In the hepatopancreas, acute Cd2+ exposure decreased the pentose phosphate pathway activity and NADPH content; however, an increased G6PDH activity and NADPH content were detected in sub-chronic Cd2+ exposure (2.86 mg/L). Morphological changes occurred in the sinus gland in crabs exposed to 2.86 mg/L Cd2+ for 3 weeks. The tightly packed structure composed by the axons, enlarged terminals, and glial cells, became loose and porous. Ultra-structurally, a large number of vacuoles and few neurosecretory granules were observed in the axon terminal. These effects added to our understanding of the toxic effects of Cd2+ and provide biochemical and histopathological evidence for S. henanense as a biomarker of acute or long-term waterborne Cd2+ pollution.

Behavioural repertory of juveniles of the freshwater crab Poppiana dentata (Randall 1840) under laboratory conditions

The behavioural repertory for Poppiana dentata has not been previously reported in literature. Therefore, this study aimed to describe the repertory of behaviours for juvenile P. dentata, under laboratory conditions. An ethogram was used to categorize activities into seven main behavioural acts; foraging, eating, grooming, locomotion, quiescence (inactive), prolonged agonism and non-agonistic contact. Juvenile daily behaviour (n = 12) were continuously recorded over 72 hr and the time durations for each behavioural act were determined from viewing video footage (n = 864 hr). Activities over 24 hr were derived from percent daily proportions of each behavioural act. Overall, juvenile crabs spent most of their time foraging (54.8%) and resting (quiescence; 25.4%), while they performed eating (11.1%), grooming (5.3%), locomotion (2.6%) and displayed agonism (0.8%) to a lesser extent. Diurnal differences between light and dark phases were significant for foraging, quiescence and eating (P < 0.05). Time spent on grooming, locomotion and prolonged agonism were higher in the light phase versus the dark but these photoperiodic variations were not significant (P > 0.05). High occurrences of non-agonistic contact were similarly observed for light (101 events) and dark (93 events) phases, reflecting a gregarious nature for the juvenile stage of P. dentata. This behavioural repertory represents the first ethological description reported for the species.

A new species of the freshwater crab genus Potamonemus Cumberlidge &amp;amp; Clark, 1992 (Crustacea, Potamonautidae) endemic to the forested highlands of southwestern Cameroon, Central Africa

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. Potamonemusmansp. 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.