Diaptomid Copepods Research Articles

Anticipating the impacts of climate change on diaptomid copepod richness in the La Plata Basin: insights for conservation planning and climate refuge identification

Anticipating the impacts of climate change on diaptomid copepod richness in the La Plata Basin: insights for conservation planning and climate refuge identification

Elucidating the Disrupted Seasonal Cycle of Eodiaptomus japonicus (Calanoida, Copepoda) in Lake Biwa: Insights from an Individual-Based Model

The seasonal fluctuations of the copepod Eodiaptomus japonicus, which dominates the zooplankton community of Lake Biwa, have been disrupted several times over the past 45 years. The aim of this study was to clarify the primary environmental factor that caused the disrupted seasonal cycle in population density of E. japonicus. Here, we tested the hypothesis that the disruption in their seasonal cycle was due to the impacts of water temperature, food conditions, and predator pressure, using an individual-based model (IBM). Based on the experimental data from the literature, we described the growth and reproduction of E. japonicus using temperature- and food-dependent functions. Previously, the developmental time of this species was expressed using Bělehrádek’s equation. In this study, we applied the Kontodimas equation, which successfully reproduced the effects of food scarcity at higher temperatures. Additionally, the influence of predators was incorporated into the survival rate of adult individuals. The long-term data set of Lake Biwa was input into the developed model to simulate the population fluctuations during the disruption period (1975–1979) and stable period (1995–1999) of their seasonal cycle. The combination of environmental data to be input was (1) water temperature, food availability, and predators; (2) water temperature and food availability; and (3) water temperature and predators. Disruptions in the seasonal cycle of the population were only observed in scenario (1) during the disruption period simulation, suggesting that the disrupted seasonal cycle of this species in Lake Biwa may have been caused by the effects of both food condition and predators. The results of simulation scenarios (2) and (3) indicated that predators have a stronger impact on the population than food availability. This time, we used common and simple indicators to describe food conditions and predators, but the model can be improved to be more complex and accurate as more data become available. Such models are important tools for understanding the relationship between environmental factors and the dynamics of diaptomid copepod populations.

Mastigodiaptomus galapagoensis n. sp. (Crustacea: Copepoda: Diaptomidae), a possibly extinct copepod from a crater lake of the Galápagos archipelago.

A new species of a Neotropical diaptomid copepod is described based on individuals recovered from a small, almost forgotten collection of unique plankton samples from El Junco, a crater lake in San Cristóbal island, Galápagos archipelago. This copepod was regularly reported (1966-2004) as an abundant zooplankter in the lake, but it was not found in subsequent plankton surveys (2007-2018), and its specific identity remained unknown. In 2020, it was declared extinct because of introduced fish predation, rotenone treatment, and other major disturbances. The taxonomic examination of these invaluable specimens allowed us to recognize them as representing an undescribed species of the freshwater diaptomid genus Mastigodiaptomus Light, 1939. Here, we describe the new species from El Junco crater lake, located in the San Cristóbal island a part of the Galápagos archipelago, collected with plankton nets. The description is based on detailed morphology, based on SEM and light microscopy. The taxonomic examination of these invaluable specimens allowed us to recognize them as representing an undescribed species of the freshwater diaptomid genus Mastigodiaptomus Light, 1939. The new species was readily assigned to this genus and is distinguished from its known congeners by details of (1) the male right fifth leg terminal claw and aculeus, (2) spiniform processes pattern of the right geniculate antennule segments 10-16, (3) length and structure of the spiniform process of the antepenultimate segment of the male right antennule, and (4) details of the dorsal process on the female fourth pediger. This finding represents the first report of this Neotropical copepod genus outside its original biogeographic region, the third species of a diaptomid copepod reported from insular freshwater systems, the southernmost record of Mastigodiaptomus, and the only freshwater calanoid in the Galápagos. The intriguing presence of this chiefly Neotropical copepod genus here could be related either to (1) human agency linked to pirate activities, commercial travelling by Spaniard ships, whaling activities, and intense tortoise hunting in San Cristóbal island. In the past, El Junco was the only freshwater source 600 nautical miles around, or (2) zoochory of resistant dormant stages passively transported by more than 65 migrating bird species known to settle in San Cristóbal. These two hypotheses cannot be properly tested at this time, so the explanation of the presence of this copepod will remain as a new open question in the fascinating natural history of the Galápagos.

Diversity of the genus Tropodiaptomus Kiefer, 1932 (Crustacea, Copepoda, Calanoida, Diaptomidae) in Thailand, with the description of two new species

Tropodiaptomus is a genus of diaptomid copepods with 10 species currently recorded in Thailand. A recent study on DNA taxonomy revealed putative new species among specimens collected from freshwater habitats throughout Thailand. This study examined the morphological characteristics and confirmed the taxonomic status of the two putative new species of Tropodiaptomus. Results showed that the two new taxa were different from other species in the genus Tropodiaptomus. These two new species, T. pedecrassumsp. nov. and T. longiprocessussp. nov., were described and illustrated based on material collected from a swamp in northern Thailand and a pond in western Thailand, respectively. They were distinguished from their congeners by the length of the spinous process on the antepenultimate segment of the adult male right antennule, the number of lobes and serration pattern on the inner margin of the adult male left P5, and the shape and supplementary process on the surface structures of basis and distal exopod segments of the adult male right P5. These discoveries increased the number of records of this genus in Thailand to 12 species. A pictorial key to all species is provided, and their ecological and biogeographical distributions are updated and discussed.

Phyllodiaptomusparachristineae, a new species of copepod (Copepoda, Calanoida, Diaptomidae) from the floodplain of the lower Mekong River Basin in Thailand and Cambodia.

Phyllodiaptomus (Phyllodiaptomus) parachristineaesp. nov., a new diaptomid copepod, was collected from 30 sites in the lower Mekong River Basin floodplain in northeastern Thailand and nine sites in Cambodia. The new species is the 13th species of the genus to have been recorded across Asia. It has a wide range of habitats, occurring in small to large, temporary to permanent water bodies, and it can be found at any time of the year. The morphology of the new species is most similar to that of the males of P. (P.) christineae, having a comb on the antepenultimate segment on the right antennule, symmetrical caudal rami, a narrow hyaline lamella on the left P5 basis, a distal accessory spine on the right P5Exp-2, and a single-lobed Enp on the right P5. On the other hand, the males of the new species have second and third urosomites without hair-like setae on the ventral margin, a rounded distal margin of the P5 intersclerite plate, a semi-circular lamella on the right P5 basis, a strong principal lateral spine inserted at the proximal 1/3 of the right P5Exp-2, and a two-segmented left P5Enp. Morphological differences among species in the subgenus Phyllodiaptomus (Phyllodiaptomus) as well as the distribution and habitats of the 13 species and two subspecies of Phyllodiaptomus in Asia are discussed.

The Diaptomidae (Copepoda, Calanoida) of Tunisia and the role of spatial and environmental factors as drivers of their distribution patterns

Even in a biodiversity hotspot such as the Mediterranean basin, aspects relating to the distribution of some groups of microcrustaceans still need clarification. In this paper, we critically analyse the available information on diaptomid copepods in Tunisian inland waters and, based on the largest sampling campaign to date carried out in the country, report new data on their distribution. In the frame of this study, 248 crustacean samples were collected from 190 sites, and 10 diaptomid species belonging to 7 genera and 2 subfamilies were found in the samples. Their distribution follows a climate gradient determined by precipitation, and ecological variables mainly affect diaptomid distribution in the study area, while pure spatial factors are of negligible importance. Diaptomid biodiversity is therefore strongly linked to the diversity of inland waters that characterise the country. This is especially true in the wetlands of the Medjerda alluvial plain, where six diaptomid species co-occurred sympatrically, with up to four or five species coexisting syntopically and synchronically in some sites. Unfortunately, the natural water bodies of this plain are currently strongly threatened by urban expansion and agricultural reclamation, and the risk of local extinction for the species they host is increasingly high.

Distribution and Diversity of Diaptomid Copepods in Freshwater Habitats of Cambodia (Crustacea: Copepoda: Calanoida: Diaptomidae)

Freshwater diaptomid copepods in Cambodia are poorly studied, and only seven taxa were known previously. From February to October 2007, 255 samples were collected from 237 freshwater sites in nine provinces representing four regions (northwest, Cardamom and Elephant Mountains, Mekong Lowlands, and east) of Cambodia. Diversity, seasonal occurrence, geographical distribution of each species, and a checklist of diaptomid copepods are documented. In this case, 24 species were recorded, including two undescribed species belonging to the genera Phyllodiaptomus and Tropodiaptomus. In this case, 14 species are recorded for the first time in Cambodia, and Mongolodiaptomus formosanus has been recorded for the first time in Southeast Asia. One species appears to be endemic to Cambodia and nine to the lower Mekong River Basin. Mongolodiaptomus malaindosinensis was the most common, frequently recorded throughout the four regions (40.5% of the sampled sites), followed by Vietodiaptomus blachei (39.2%), Eodiaptomus phuvongi (38.8%), Mongolodiaptomus formosanus (31.2%), and Eodiaptomus draconisignivomi (27.4%). Very rare species such as Eodiaptomus sanoamuangae, Tropodiaptomus vicinus, Mongolodiaptomus calcarus, and Tropodiaptomus sp. were only recorded at 0.4% to 0.8% of the sampled sites. The species diversity of Cambodia is most similar to that of Thailand, where 22 species (91.6%) occur both in Cambodia and Thailand, and 12 (50%) of the species have been recorded in both Cambodia and Vietnam.

NEW RECORD OF LIGULA INTESTINALIS (LINNAEUS, 1758) (CESTODA: PSEUDOPHYLLIDEA) INFECTION IN HYPSELOBARBUS THOMASSI FROM THE WESTERN GHATS OF KERALA

The tapeworm Ligula intestinalis (L.) is the most common species of the genus Ligula and is widely distributed throughout the northern hemisphere (Dubinina, 1980). It has recently been also reported from southwestern Australia (Morgan, 2003; Chapman et al., 2006). This pseudophyllidean cestode presents a complex life cycle with a cyclopoid or diaptomid copepod as first intermediate host and planktivorous fish as second intermediate host. Fish-eating birds serve as the final host in which L. intestinalis quickly reaches sexual maturity and releases eggs. The worms acquire maturity in 3-5 days in the bird host and infected piscivorous birds are scarcely observed in natural conditions (Loot et al., 2001). The most conspicuous stage within the life cycle is the plerocercoid. Although it develops in the abdominal cavity of the second intermediate host and has a considerable effect on fish health, fecundity and behaviour. As a result it can cause heavy losses in freshwater pisciculture (Arme and Owen, 1968; Carter et al., 2005). Particularly reported from cyprinid fish, L. intestinalis has been shown to utilize a broad range of hosts, including other fish families such as Catostomidae, Salmonidae or Galaxiidae (Dubinina, 1980; Chapman et al., 2006).

Loss of a freshwater copepod species from El Junco Lake, Galápagos following the introduction and eradication of the Nile tilapia

Abstract An undescribed diaptomid copepod probably belonging to a new Mastigodiaptomus species has been discovered and was very abundant in El Junco Lake (San Cristóbal Island, Ecuador) from 1966 until 2004. The species was not found in samples from 2007, 2008 or 2018. The loss of this key species from the lake coincides with the illegal introduction of Nile tilapia to El Junco Lake in 2005 and its subsequent eradication in 2008. The disappearance of this biogeographically and ecologically important copepod population may be explained by direct mechanisms of predation and competition, by a combination of both processes, and by indirect mechanisms linked to alterations in the lake ecosystem. The effects of fish eradication using rotenone may have contributed to the loss of the diaptomid population and to preventing its recovery. This article discusses the search for sources of propagules for recolonization and possible reintroduction scenarios and procedures.

Historical Zooplankton Composition Indicates Eutrophication Stages in a Neotropical Aquatic System: The Case of Lake Amatitlán, Central America

This paper presents a study of freshwater zooplankton biodiversity, deemed as a reliable indicator of water quality. The Guatemalan Lake Amatitlán, currently used as a water source, has shown signs of progressive eutrophication, with perceptible variations of the local zooplankton diversity. Biotic and abiotic parameters were determined at four sites of Lake Amatitlán (Este Centro, Oeste Centro, Bahía Playa de Oro, and Michatoya) in 2016 and 2017. The local composition, the species richness and abundance of zooplankton, and the system environmental parameters were analyzed during both years surveyed. Biological data suggesting eutrophication of this tropical system were obtained, including a high rotifer abundance (11 species: the rotifers Brachionushavanaensis (109 ind L−1) and Keratellaamericana (304 ind L−1) were the most abundant species in this lake). The presumably endemic diaptomid copepod species, Mastigodiaptomusamatitlanensis, was absent in our samples, but we report the unprecedented occurrence of two Asian cyclopoid copepods (i.e., Thermocyclopscrassus and Mesocyclops thermocyclopoides) for Lake Amatitlán and Guatemala. The presence of larger zooplankters like adults and immature copepods (i.e., Arctodiaptomusdorsalis) and cladocerans (Ceriodaphnia sp.) at site “Este Centro” indicates a relatively healthy zooplankton community and represents a focal point for managing the conservation of this lake.

Diversity, Distribution, and Habitat Occurrence of the Diaptomid Copepods (Crustacea: Copepoda: Diaptomidae) in Freshwater Ecosystems of Thailand

The diversity, distribution, and checklist of diaptomid copepods from various freshwater ecosystems throughout Thailand are presented, based on data from our biodiversity projects during 1993–2019 and literature reviews. Thailand has one of the most diversified diaptomid fauna in the world, with 42 species identified from 2150 localities (4962 samples). Mongolodiaptomus has the highest species richness with ten species, followed by Tropodiaptomus with seven species. Among these, eight taxa (Arctodiaptomus sp., Mongolodiaptomus pectinidactylus, Neodiaptomus meggitti, Tropodiaptomus hebereri, T. lanaonus, T. oryzanus, T. ruttneri, and Paradiaptomus greeni) are new to the fauna of Thailand. The rare P. greeni, which predominantly occurs in Africa, is also a new record for Southeast Asia. The most frequently encountered species were Mongolodiaptomus botulifer, Phyllodiaptomus praedictus, M. calcarus, M. dumonti, M. malaindosinensis, Vietodiaptomus blachei, Phyllodiaptomus christineae, Eodiaptomus sanoamuangae, Neodiaptomus yangtsekiangensis, E. draconisignivomi, T. vicinus, and Heliodiaptomus elegans. Twelve species appear to be endemic to Thailand, and eight species occur only in the countries belonging to the lower Mekong River Basin (Thailand, Cambodia, Laos, and Vietnam). The uniqueness of the Thai diaptomids is a high degree of co-occurrence of four to seven species in the same localities. Comments on the taxonomic status of the species recorded are provided. In addition, the taxonomic validity of Mongolodiaptomus malaindosinensis is discussed.

Phenetic and Genetic Variability of Continental and Island Populations of the Freshwater Copepod Mastigodiaptomus ha Cervantes, 2020 (Copepoda): A Case of Dispersal?

The diversity of freshwater zooplankton is still little known in Mexico, particularly in reference to insular zooplankton communities. Diaptomid copepods (Crustacea: Copepoda: Calanoida) are a widespread group worldwide, and Mexico harbours high diaptomid diversity. Based on a recent sampling of freshwater zooplankton on a Caribbean Island of Mexico, we present the first record of a diaptomid copepod from an island freshwater ecosystem. It shows the well-known tendency of Neotropical diaptomids to have restricted distributional patterns and high levels of endemism. The species recorded, Mastigodiaptomus ha (Cervantes-Martínez, 2020) appears to have a restricted distribution in the Yucatan Peninsula (YP), and the island as well. In order to explore potential differences between the island and continental populations of this species, its phenetic and genetic diversity was analysed by performing morphological comparisons and also by exploring differences of the habitat conditions and genetic sequences (CO1 gene). Our analysis revealed a low (average = 0.33%) genetic divergence between both populations; likewise, both the morphology and habitat conditions closely resemble each other in these two populations. The low genetic divergence between the continental and island populations of M. ha suggests an early common origin of the species in the geological history of the YP.

What is the impact of urban development and thermokarsting on arctic tundra pond zooplankton communities?

Human development and warming in the Arctic are increasingly putting new pressures on the abundant freshwater ecosystems in the region. In particular, recent and rapid expansion of thermokarst ponds in permafrost regions has been associated with these stresses. Our goal was to examine the relative impacts of pond enrichment by urban encroachment and thermokarsting, compared to relatively unimpacted regions, on the environmental conditions and zooplankton communities of tundra ponds near Utqiaġvik, AK, USA. Both urban ponds and thermokarst ponds were found to have substantially different environmental conditions, as well as distinctive zooplankton communities relative to reference sites. Thermokarst ponds presented an environment rich in DOC and nutrients (N, P, and Si) and phytoplankton biomass. Enrichment by nutrients and DOC in thermokarst ponds led to significantly greater zooplankton abundance composed largely of Daphnia middendorffiana (66 individuals L−1) and cyclopoid copepods (65 individuals L−1). Urban ponds had moderate nutrient levels, with elevated benthic algal biomass. These ponds had intermediate numbers of D. middendorffianna (14 individuals L−1), as well as significantly higher numbers of diaptomid copepods (8 individuals L−1) and chydorids (11 individuals L−1), as compared to one or both reference regions. The two reference regions [Barrow Environmental Observatory (BEO) and International Biological Program (IBP)] had consistently lower nutrient concentrations, algal levels, and zooplankton abundances (less than 3 individuals L−1). Finally, harpacticoid copepods and Bosmina longirostris were new records for the zooplankton in the region. Further collections are required to determine the drivers for these new observations. These results identify the large potential relative contributions of urban inputs and thermokarsting to enrichment of Arctic aquatic ecosystems and point to thermokarsting, which will likely increase with warming, as a major contributor to change in these systems.

Hybridization in Selected Species and Genera of Diaptomid Copepods in China

To better understand the fauna of freshwater calanoid copepods of China, including the occurrence of intra- and intergeneric hybridization, we studied five species, distributed across the whole of China or in South China. We sequenced a mitochondrial (COI) and the nuclear ribosome 18S operon (ITS) to reconstruct the phylogenetic trees by using a Bayesian and maximum likelihood (ML) approach with 161 individuals. The phylogeny tree revealed five clades and two geographically separated subclades in both S. ferus and P. tunguidus. We found, for the first time, that the hybrid specimens occurred in Diaptomidae, but low hybridization suggested effective barriers to hybridization and introgression. One hypothesis, that hybridization is recent and was initiated by invasions via canals built between the Yangtze and Pearl rivers c. 2000 years ago, is not supported by K2P genetic distances of the order of 20%. Furthermore, COI analysis of different populations of S. ferus and P. tunguidus revealed two geographical clades in each species, with genetic distances commensurate with cryptic speciation. Both clades occupy subranges maintained without visible barriers to mixis.

First record of <em>Arctodiaptomus wierzejskii</em> (Richard, 1888) (Copepoda Calanoida Diaptomidae) from Malta

Diaptomid copepods belonging to the genus Arctodiaptomus Kiefer, 1932 were collected in two temporary water bodies in Malta. The morphological identification of the collected specimens proved that they belong to Arctodiaptomus wierzejskii (Richard, 1888) even if a morphological peculiarity pertaining to the morphology of the male right antennule of the Maltese populations was observed and here briefly discussed. This finding constitutes the first record of a calanoid copepod from the inland waters of the Maltese Islands.

On the Occurrence of Metadiaptomus chevreuxi (Calanoida, Diaptomidae, Paradiaptominae) in the Iberian Peninsula, With Notes on the Ecology and Distribution of its European Populations

Temporary ponds are one of the most peculiar ecosystems in the world, being characterized by an extraordinarily rich crustacean fauna, with a high degree of endemism. Among them, diaptomid copepods are among the most biogeographically interesting taxa. However, the present knowledge on diaptomid distribution is still far from being exhaustive, even in the relatively well-studied western European countries. In this study, we report the first record of the diaptomid calanoid copepod Metadiaptomus chevreuxi for the Iberian Peninsula, where it was collected in five temporary ponds in Andalusia (Spain). The characteristics of the new sites are described, the literature dealing with the European localities of the species is reviewed, and a molecular phylogenetic tree has been built, based on new and previously available mitochondrial DNA sequences, thus expanding the knowledge on the ecology and phylogeography of this rare species. The species mainly occupies small isolated temporary ponds in (semi-)arid regions, suggesting adaptations to unpredictable aquatic habitats. The existence of two molecular clades separating the Iberian from the Sicilian and Tunisian populations supports the existence of a longitudinal long-term disjunction, whereas the north-south flow is probably facilitated by migrating birds. Further research on the biota of the small water bodies of the western Mediterranean area may help to expand our knowledge on rare aquatic species, such as M. chevreuxi, and to better interpret their natural history.

On the occurrence and distribution of Calanipeda aquaedulcis Kritschagin, 1873 (Copepoda, Calanoida, Pseudodiaptomidae) in Sicily, Italy, with some notes on coexistence and species replacement in calanoid copepods

The only population of the pseudodiaptomid copepod Calanipeda aquaedulcis Kritschagin, 1873 to date reported to occur in Sicily disappeared at the beginning of the XXI century due to deep environmental changes which affected the single site (Lake Biviere di Gela) known for this species on the island. In that site C. aquaedulcis is now replaced by Copidodiaptomus numidicus (Gurney, 1909), a diaptomid copepod whose distribution has been greatly increasing since the second half of the last century. In the present note, the occurrence of C. aquaedulcis in 12 novel water bodies spread throughout Sicily is reported, and some environmental data on the sites where the species was collected are provided. Moreover, in a few sites C. aquaedulcis was found to co-occur with Copidodiaptomus numidicus. The recorded co-occurrence of these two species and the replacement of C. aquaedulcis with C. numidicus in Lake Biviere di Gela are briefly discussed.

Allodiaptomus nongensis, a new diaptomid copepod (Copepoda: Calanoida) from a tributary of the Mekong River, with notes on its consumption by local people in Central Laos

A new calanoid copepod, Allodiaptomus nongensis n. sp., is herein described based on samples collected from the Xe Lanong River (a tributary of the Mekong River), and 13 other localities in Central Laos. This is the sixth species of the genus Allodiaptomus Kiefer, 1936. The other five members in the genus were recorded from India, South China, Cambodia, Thailand, and Vietnam. The features that stand out in the new species are in the male: the right caudal ramus has a large, biacuminate, conical process proximally, and the Exp-2 of the right P5 has a hook-shaped principal spine proximally. The new species is abundant in both temporary and permanent waters, but is restricted to Savannakhet Province. This Laotian endemic copepod is referred to by local people as “Pa Khayong”, which means tiny fish. Since high densities of this copepod can be found in the dry season (December until May), several man-made copepod traps are placed by local people along the river banks in Muang Nong District. Interestingly, large concentrations of individuals (body length: ~1 mm) belonging to the new species are harvested and consumed by these villagers. Additional information about this species and the copepod fisheries by local people in this area is provided herein. In this paper, the reassignment of Allodiaptomus rarus to the genus Mongolodiaptomus is proposed.

Updated checklist and distribution of the diaptomid copepods (Copepoda, Calanoida, Diaptomidae) of China

We present an updated checklist of the Diaptomidae of China, based on a literature review and on original field data from all over China during 2012-2016. A total of 19 genera and 56 species have been recorded.Neutrodiaptomushas the highest species richness (10 species), followed byArctodiaptomus(9 species). Only one species each ofEudiaptomus,Mixodiaptomus,Eodiaptomus,Dentodiaptomus,Dolodiaptomus,Allodiaptomus,Karstodiaptomus,MetadiaptomusandParadiaptomuswas found. The taxonomic status of 16 species was revised: one wrongly attributed genus,Argyrodiaptomus, was corrected toSinodiaptomus. First records for China includeArctodiaptomus parvispineusand one new cave-dwelling genus,Karstodiaptomus, is added. One Latin name from Shen & Sung’s book (1979) is corrected. Remarks on nomenclature and taxonomic issues are supplemented with information on the geographical distribution of the various species within China.

A new species of Mongolodiaptomus Kiefer, 1938 from northeast Thailand and a key to the species (Crustacea, Copepoda, Calanoida, Diaptomidae).

This study describes the new species Mongolodiaptomus loeiensis sp. n. collected from a temporary pond nearby a cave located in Loei Province, in northeastern Thailand. Mongolodiaptomus loeiensis sp. n. is similar to M. calcarus (Shen & Tai, 1965) in the male but can be distinguished from its congeners by the following unique characteristics in the males: (1) the right caudal ramus has 3 ventral chitinous prominences; (2) intercoxal plate of P5 is produced into 2 spine-like lobes on distal margin; (3) the basis of right P5 has a subglobular chitinous prominence on mid-distal caudal surface; and (4) the principal lateral spine on the right Exp-2 P5 is extremely bent at its tip. The occurrence of diaptomid copepods in the study area is discussed and an identification key to worldwide species of the genus Mongolodiaptomus Kiefer, 1938 is presented herein.