Cadmium (Cd) is an extremely toxic heavy metal and widespread in the environment, which has been demonstrated closely associated with numerous organs damage and even death. To evaluate the signaling pathway and the toxicity induced by Cd2+ in aquatic organisms, freshwater crabs Sinopotamon henanense were exposed to Cd2+ (0, 14.5, 29 and 58 mg/L) for 4 d. The results showed that Cd2+ induced the increase of diacylglycerol (DAG) and inositol-1,4,5-triphosphate (IP3), the rapid change of Ca2+ concentration in the cytoplasm and activation of protein kinase C (PKC) in the gill of crab. Also, Cd2+ raised the expressions of 6 genes relating with protein detoxification and folding, including cytochrome P450 (CYP450), BAG regulator 3 (BAG3), protein disulfide isomerase (PDI) and 3 genes encoding heat shock proteins (Hsp21, Hsp27 and Hsp70). And, it was observed that Cd2+ exposure aggravated filament swelling and raised the number of dead epidermal cell in gill. Meanwhile, Cd2+ exposure degraded DNA which was accompanied by an obvious decrease in ATP level. In conclusion, Cd2+ triggered DAG-PKC/IP3-Ca2+ double signaling pathway, caused gene expression, DNA degradation and ATP decrease, and finally induced the cell injury in S. henanense based on histological observation. This study would provide us fundamental information to discover the underlying mechanism of Cd2+-induced cytotoxicity.

Isolated island endemic crabs: Fine-scale genetic population structure of an endangered freshwater crab, Geothelphusa miyakoensis

The present study was conducted to assess the diversity, distribution, and morphometric characteristics of freshwater crabs inhabiting the tributaries of the Godavari River system across Nanded, Hingoli, and Parbhani districts in Maharashtra. Extensive field surveys were carried out between June 2023 and June 2025 in various freshwater habitats, including rivers, tributaries, streams, lakes, farming areas and ponds. Some areas yet to be remain study and surveys. Specimens were collected manually and identified based on their external morphological features. A total of two crab species belonging to the genus Barytelphusa were recorded such as Barytelphusa guerini and Barytelphusa cunicularis. Among them, B. guerini was the most widely distributed, occurring in several tributaries such as the Aasna, Manyad, and Kayadhu rivers, whereas B. cunicularis was restricted to deeper and stable water bodies. Distinct variations in body coloration, size, and chela structure were noted between species. Morphometric analysis showed clear sexual dimorphism, with males exhibiting larger carapace dimensions, heavier body weight, and more robust chelae, while females possessed broader abdomens adapted for egg carrying. The findings highlight the Ecological richness of the Godavari-river basin and the adaptive diversity of its freshwater crab Fauna. Despite moderate anthropogenic pressure, these tributaries continue to support stable crab populations. The data generated in this study serve as a baseline for future ecological monitoring, biodiversity assessment, and conservation planning of freshwater ecosystems in the Marathwada region.

The freshwater crab Paratelphusa jacquemontii is a vital component of aquatic ecosystems in South Asia, particularly in India, Sri Lanka, and Bangladesh. While it plays a key role in nutrient cycling and serves as a food source, concerns have emerged regarding its potential toxicity due to bioaccumulation of environmental pollutants. The accumulation of heavy metals (Cd, Pb, and Hg) and pesticide residues in crab tissues (muscle, gills, and hepatopancreas) obtained from contaminated and reference sites is assessed in this work. The findings showed that crabs from industrial areas had far higher concentrations of Pb and Cd. Hepatopancreas > gills > muscle was the order of tissue-specific accumulation. Seasonal differences showed that pesticide residues were higher during the monsoon season. These results point to possible health and ecological dangers connected to eating infected crabs. The study emphasizes the necessity of ongoing observation and better environmental management techniques.

Abstract The decapod crustacean Barytelphusa cunicularis (Westwood in Sykes, 1836) (Gecarcinucidae) is among the world’s largest freshwater crabs, with both ecological and economic significance. The crab species inhabits diverse aquatic habitats throughout peninsular India, including the Western Ghats. Although commensal associations between invertebrates (including crustaceans) and aquatic insects are widespread, no previous records exist of brachyurans hosting immature chironomids (Diptera: Chironomidae). This study documents the first commensal association between B. cunicularis (Brachyura) and chironomid larvae and pupae, based on field surveys during the dry season in the Kalsubai Harishchandragad Wildlife Sanctuary, Maharashtra. Of 28 crabs examined, 23 harboured chironomid larvae or pupae, most commonly occurring in their subbranchial region, especially in subadults with pre-existing exoskeletal deformities. No infestations were detected in crabs collected during the rainy season or among more terrestrial species, indicating strong seasonal and ecological specificity. Observed deformities in regions where larvae were present appeared to predate their occurrence and were likely related to moulting or environmental stress; there was no evidence that chironomid larvae caused further host damage, supporting a commensal, rather than parasitic, relationship. A potential benefit to the larvae may include passive transport via the host, although this requires further investigation. These findings expand the recognised host range of chironomids and underscore the ecological plasticity of this symbiosis, highlighting the need for further taxonomic and ecological investigation.

A new species of freshwater crab from the Democratic Republic of the Congo, Central Africa is described based on previously unidentified museum material. Potamon (Potamonautes) johnstoni stappersi Balss, 1936, also from the D. R. Congo, is here recognized as a valid species and redescribed following examination of the type material and other specimens from Tanzania. The new taxa are assigned to Arcopotamonautes Bott, 1955, based on a combination of characters of the carapace, chelipeds, mouthparts, and gonopods. These species are compared to, and distinguished from, similar Arcopotamonautes species found in Central and East Africa. Illustrations and a distribution map are provided.

Until recently, the Karpathos water frog (Pelophylax cerigensis) was considered endemic to Karpathos Island (Greece) and has recently been reclassified by the IUCN as Endangered (EN), having been previously assessed as Critically Endangered (CR). The species faces severe threats primarily associated with the scarcity of freshwater bodies in the southern Aegean Sea. Over the past decade, demographic assessments have revealed a marked population decline, driven by the intensifying effects of climate change, including reduced rainfall, and increasing summer temperatures. In addition, the few natural ponds that persist during the dry summer months are often shared with the Levantine freshwater crab (Potamon potamios), resulting in increased frog mortality due to predation. Despite these challenges, recent developments provide cautious optimism. These include the construction of a dam in southern Karpathos and the taxonomic reassessment of the water frog population on the neighboring island of Rhodes as conspecific with P. cerigensis. In response to the species' precarious status, the Hellenic Herpetological Society designed and implemented a National Action Plan aimed at the protection and conservation of the Karpathos water frog. The Action Plan includes a series of targeted mitigation measures, such as the construction of artificial ponds to retain water during the summer, as well as a hydrological study addressing the seasonal drying of the ecologically important Eleimonitria spring. A key component of the Action Plan involves education and outreach initiatives targeting primary school students, local residents, and visitors, highlighting the frog's ecological importance and conservation needs. Informational brochures will be distributed across the island to raise awareness of the species' conservation status and the importance of safeguarding its habitat. The implementation of this Action Plan aims to secure the long-term survival of the Karpathos water frog and to strengthen integrated conservation efforts across its extremely limited range.

During the present study species boundaries we examined in the freshwater crab species complex (comprising Potamonautes clarus Gouws, Stewart & Coke, 2000 and P. depressus Krauss, 1843). DNA sequence data from three mitochondrial loci and one nuclear locus were used for additional specimens sampled along the Drakensberg Mountains, KwaZulu-Natal Province, South Africa. Phylogenetic analyses using Bayesian Inference and Maximum Likelihood platforms incorporating additional sample localities using a total evidence DNA sequence dataset revealed the presence of a monophyletic Drakensberg Mountain group comprised of four main clades. Clade A comprised specimens from Impendle, Karkloof Nature Reserve, Injisuthi and Dargle Forest sister to clade B. The latter clade comprised specimens from Ngome Forest sister to P. clarus (from Oliviershoek Pass, and Gudu Falls) sister to Paardeplaats Nature Reserve. Clade (B) was sister to P. baziya Daniels, Marais, Barnes & Gouws, 2021 (clade C) that was sister to the remainder of clade D that comprised specimens from Himeville, Bushmans Nek, Rougham, Vergelegen Nature Reserve, Coleford Nature Reserve, Sani Pass and Garden Castle Nature Reserve. Clade A was collected closest to the type locality in the near eastern Drakensberg Mountains and is here designated P. depressus s.s., whereas specimens from Ngome Forest and Paardeplaats Nature Reserve are designated as P. ngomiensis sp. nov. and P. paardeplaatsie sp. nov. respectively, whereas the clade from the southern Drakensberg Mountains (clade D) is here designated as P. drakensbergie sp. nov. and sister to P. baziya. Divergence time estimation revealed Pliocene-Pleistocene cladogenesis. Climatic ameliorations are recognised as the main driver of speciation in the species complex. The three new potamonautid freshwater crab species are herein described and a neotype is designated for P. depressus s.s. to stabilise the taxonomy of the species. ZooBank: urn:lsid:zoobank.org:pub:954D6BEA-075F-4DAA-8D27-CCBEAC459FE3.

The taxonomies of two species of freshwater crabs from Tanzania and Kenya, the river and stream-living A. johnstoni (Miers, 1885) and the threatened lake endemic Arcopotamonautes platycentron (Hilgendorf, 1897) are revised based on examination of the holotypes. Updated diagnoses, illustrations, and distribution maps are provided for these species, and their conservation status is discussed. DNA sequence data of the mitochondrial cytochrome one locus (CO1) between the two aforementioned species indicate a close evolutionary relationship as evident from an unexpectedly low uncorrected CO1 ‘p’ distance of 1.51% that would not normally be considered enough to warrant their recognition as two separate species. On the other hand, it is possible that the distinctly separate habitats of the two species (lake versus streams and rivers) may have given rise in a relatively short evolutionary time for rapid ecological speciation to have produced the numerous morphological changes observed in the lake species.

Paragonimus spp. are foodborne trematodes with complex life cycles involving freshwater snails and decapod crustaceans. In Central America, Paragonimus mexicanus is a known zoonotic agent, whereas the public health significance of P. caliensis remains unclear. Between 2015 and 2016, we surveyed freshwater crabs across 51 sites in 15 river basins spanning three major climatic regions in Costa Rica. A total of 419 crabs (10 species) were examined for metacercariae; male crabs were identified morphologically, and infected females were identified to species by 16S rRNA and COI sequencing. Metacercariae were detected in six crab species, three of which represent new hosts of Paragonimus. The highest prevalence in male crabs occurred in Ptychophallus uncinatus (55.6%, 25/45). Molecular analyses confirmed the presence of two Paragonimus species in crabs: P. mexicanus and P. caliensis. A binomial GLM showed that males had higher odds of infection than females (p = 0.0059). Most infections occurred in areas along the Caribbean coast and in the Northern Region, which drains into Lake Nicaragua and Río San Juan. A binomial GLM revealed that the probability of Paragonimus infection varied significantly across climatic regions. Crabs from the Caribbean slope had the highest odds of infection, followed by the Northern Region. In contrast, crabs from the Pacific slope were significantly less likely to be infected. These patterns support the existence of geographic clusters of transmission within Costa Rica. We provide the first species-level, molecular confirmation of infected female crabs in Costa Rica and identify three freshwater crab species as newly recognized second intermediate hosts. These findings expand the known host range and distribution of Paragonimus in Costa Rica and highlight the need for public health education about the risks of consuming undercooked freshwater crabs.

Abstract Paragonimus is the only genus in the family Troglotrematidae. Dogs, cats and other mammals may become infected by consuming crabs or shrimp harbouring metacercariae. A 1.11‐year‐old cat was presented with chronic coughing episodes. Thoracic radiography and ultrasonography suggested diffuse pneumonia. Cytology from a pulmonary granuloma and faecal examination revealed numerous trematode eggs (50–100 µm) consistent with Paragonimus spp. Molecular analysis of faecal DNA confirmed 100% nucleotide identity with Paragonimus mexicanus metacercariae previously reported from freshwater crabs in Puntarenas, Costa Rica. Antiparasitic therapy combining praziquantel, pyrantel and mebendazole resolved clinical signs. This case highlights the importance of including paragonimiasis in the differential diagnosis of cats with chronic respiratory disease in Central America, where aquatic intermediate hosts and wild reservoirs are abundant, even in peri‐urban settings.

ABSTRACT Island biogeography provides a crucial framework for interpreting global biodiversity patterns; however, the distinctive dynamics of continental islands remain underexplored relative to those of volcanic oceanic islands. This knowledge gap obscures our understanding of species dispersal and evolution, particularly on small continental islands whose connectivity has been modulated by Quaternary sea‐level oscillations. Here, we integrate double‐digest restriction‐site‐associated DNA (ddRAD) sequencing with mitochondrial COI and 16S rRNA data to investigate the phylogeography, population structure, demographic history and ecological niche of the narrowly distributed freshwater crab Nanhaipotamon nanriense inhabiting mainland and nearby islands in southeastern China. Our analyses revealed strong genetic differentiation, highlighting a deeply divergent island lineage isolated by a narrow marine channel and an inland lineage isolated by the Minjiang River. Demographic reconstructions indicated significant population expansions during lower sea level in the Pleistocene, followed by population contractions correlated strongly with post‐glacial sea level rise in the Holocene. By synthesising genomic, demographic and ecological evidence, our study demonstrates how marine inundation, riverine barriers and glacio‐eustatic cycles jointly shape the genetic and distributional patterns of continental island freshwater species and also provide critical insights for conservation strategies.

Recent explorations of caves in Pahang, central Peninsular Malaysia yielded specimens of an unusual long-legged terrestrial, cave-dwelling crab. Morphological examinations of the specimens collected, in comparison with known species from the region suggests that they belong to a new genus and species, which are described herein. Merapohra karsticola gen. nov. et sp. nov., is differentiated from other potamids by characters of the carapace epigastric and postorbital cristae, ambulatory legs, male thoracic sternum, male pleon, and diagnostic structure of the male first gonopod. The discovery of this new genus and species of cave-dwelling crab highlights the importance and high diversity of karst systems in Peninsular Malaysia, which are imperilled in light of ongoing quarrying and mining activities.

Two new species of freshwater crabs are described from a hillstream in Chixi Town, Taishan City, Guangdong Province, China: Megapleonum taishanense sp. nov. and Cantopotamon chixiense sp. nov. The two new species are sympatric and are similar in size, colour and superficial appearance in the field. Inspection of key morphological characters sets them apart as undescribed species from two different genera. Megapleonum taishanense sp. nov. and Cantopotamon chixiense sp. nov. can immediately be separated from their respective congeners by their unique G1 morphology but also their combination of carapace, maxilliped 3 and male pleon characters. A phylogeny constructed using the mitochondrial COI gene places Cantopotamon chixiense sp. nov. in its own clade as sister to C. yangxiense Huang, Ahyong & Shih 2017 and a previous 16S rRNA gene study has already shown that Megapleonum taishanense sp. nov. represents an independent clade within Megapleonum Huang, Shih & Ahyong 2018, supporting the current taxonomic treatment of both new species.

A new species of semiterrestrial freshwater crab is described from Tapah Hills in Peninsular Malaysia. Geosesarma wongi sp. nov. is the 13th member of the genus reported from the country and is most similar to G. peraccae (Nobili, 1903) and G. cataracta Ng, 1986, but easily separated by its distinct carapace features and structures of the adult male chela and male first gonopod. The types of G. peraccae are figured for the first time. Geosesarma cataracta is also figured in detail, and the type series is shown to be mixed.

Cirrodrilus osumi sp. nov. (Clitellata: Branchiobdellida: Branchiobdellidae) is described based on the specimens on the freshwater crab Geothelphusa exigua Suzuki and Tsuda, 1994 (Decapoda: Potamidae) collected from headwater areas in Osumi Peninsula, Kagoshima, southern Japan. Although the new branchiobdellidan resembles the continental East Asian Cirrodrilus kawamurai (Yamaguchi, 1934) in having four membranous large dorsal lobes on the peristomium, it differs by having shorter dorsal lobes and four pairs of small teeth in the jaws. Additionally, Ci. kawamurai is partially redescribed based on Yamaguchi's original slide collection. The Bayesian inference tree using partial mitochondrial cytochrome c oxidase subunit I sequences supported that the new species is genetically more closely related to a congener from the Korean Peninsula than to the endemic congeners from northern Japan. The finding of the new species in this study represents the record of the 12th species of the genus Cirrodrilus Pierantoni, 1905 from Japan, as well as the first record of a branchiobdellidan associated with freshwater crabs in East Asia.

The pursuit of sustainable agriculture has intensified the search for effective organic fertilizers from renewable resources. Crustacean shell waste, rich in chitin, minerals and nutrients, represents a promising yet underutilized resource for enhancing soil fertility and plant growth. This study investigated the efficacy of freshwater crab (Oziotelphusa aurantia) shell powder (CSP) as an organic fertilizer on the growth and yield of okra (Abelmoschus esculentus), in comparison to vermicompost and an unamended control. A pot experiment was conducted using red soil amended with CSP at 0.5% (w/w), vermicompost and a control. Growth parameters, including germination rate, plant height, leaf number and dimensions, flowering time and pod yield were monitored over eight weeks. CSP amendment significantly enhanced plant growth and productivity. Germination commenced one day earlier in the CSP-treated soil compared to the control and vermicompost. Plants grown in CSP-amended soil demonstrated superior performance in vegetative growth, producing a greater number of leaves, larger leaf dimensions (9 cm length, 10 cm width by week 6) and a higher final plant height. While flowering initiated slightly later than in the vermicompost group, CSP-treated plants yielded a significantly greater number of pods (12 per plant), with longer pod length (12.2 cm) heavier pod weight (11 g) and a higher total yield per plant (200 g) compared to both vermicompost (120 g) and the control (82.5 g). Freshwater crab shell powder is a highly effective organic fertilizer that significantly improves the growth, yield and nutritional quality of Abelmoschus esculentus. The utilization of this aquaculture waste product offers a sustainable strategy for enhancing agricultural productivity, improving soil health and reducing environmental pollution.

Neotropical aquatic ecosystems harbor a rich diversity of endemic species, many critically threatened by anthropic activities, such as the aeglid crabs. Hemolymph cell morphology and viability analyses offer diagnostic tools for evaluating the biological condition of species subjected to environmental stressors. This study investigates apoptotic cell ratios in freshwater crabs of the genus Aegla, exposed to anthropic impact. Hemocyte morphology and apoptosis levels were assessed in Aegla spp. collected from streams with different levels of disturbance across Brazil's southeast region. Water quality parameters were measured alongside concentrations of metals and surfactants. Sites exhibiting the lowest water quality presented significantly elevated apoptotic cell ratios. The integration of hemolymph analyses with environmental assessments revealed potential correlations between biotic and abiotic factors, offering an understanding of the relationship between immune status and ecological conditions in aeglid species. This integrative approach provides a valuable framework for informing conservation strategies for these freshwater organisms.

Potamon ibericum , a freshwater crab species, is highly sensitive to environmental changes, especially water temperature and flow regimes. This sensitivity makes it an excellent bioindicator for assessing the health and stability of freshwater ecosystems under climate change scenarios. However, its limited dispersal ability makes it vulnerable to habitat fragmentation and climate-induced range shifts. Therefore, predicting its future habitat suitability is crucial for early conservation planning. This study utilizes current and future (2060–2080) climate variables along with species distribution modeling (SMD) tools. By collecting presence records of the species from various datasets and published articles, we examined its potential distribution. The results indicated that temperature seasonality is the most significant factor influencing the species’ distribution. Additionally, with increasing climatic changes, the species’ altitude range shifts to higher elevations, averaging between 1,600 and 1,900 meters above sea level. We also assessed the degree of overlap between Iran’s protected areas and the current and future suitable habitats for the species. The findings revealed that the most important refuge is the Central Alborz Protected Area, which encompasses approximately 1,803 square kilometers of suitable habitat. However, future projections under the most severe climate scenarios suggest that less than one-fifth of the suitable habitat will remain within protected areas. In general, P. ibericum may face the risk of extinction and significant loss of suitable habitat in Iran due to extreme future climatic conditions. Protecting this sensitive and ecologically important species within freshwater ecosystems is vital, and immediate management actions are necessary to ensure its conservation.

Paragonimus westermani is a food-borne zoonotic trematode transmitted to humans through the consumption of undercooked crustaceans. Freshwater crabs act as the second intermediate host for the encysted metacercariae stage. However, accurate identification of intermediate hosts remains a challenge. Here, we aimed to detect and identify P. westermani in randomly collected freshwater crabs and determine the species of infected crabs in Davao Oriental through molecular methods. Specifically, Sanger and next-generation sequencing were conducted for species identification through BLASTn, followed by phylogenetic analyses to understand geographic and taxonomic relationships. Results showed P. westermani DNA was detected in five out of eleven crab samples and these sequences were closely grouped to the Philippine reference sequence. Through a similar approach, the infected crabs showed high sequence similarity and formed tight clustering to Isolapotamon sp. Overall, the results provided evidence that P. westermani DNA was detected in Isolapotamon sp., a genus endemic to Mindanao, and can be a potential intermediate host. This expands our current understanding of transmission ecology beyond the only known intermediate host in the Philippines, Sundathelphusa philippina.