Cladocera
Guides
Bosmina
water flea
Bosmina is a genus of small cladoceran crustaceans commonly known as water fleas. Members are distinguished from the related genus Bosminopsis by having antennae that are separated at their bases rather than fused. Bosmina species are filter feeders that consume algae and protozoans approximately 1–3 μm in size, using a dual feeding mechanism involving mesh-like setules on the second and third legs for filtering while the first leg grasps particles. The genus exhibits notable morphological plasticity, particularly in posterior mucrones and anterior antennules, which vary in response to predation pressure. Some Bosmina species have become invasive outside their native ranges, posing threats to aquatic ecosystems.
Chydorus
Chydorus is a genus of small benthic-littoral cladocerans in the family Chydoridae, established by William Elford Leach in 1816. Species in this genus are characterized by rounded, often reticulated carapaces and are among the most common anomopods in freshwater systems worldwide. The genus exhibits cosmopolitan distribution with multiple centers of diversification in Europe and Asia, and includes ecologically significant species such as Chydorus sphaericus, which dominates eutrophic waters and plays important roles in food web dynamics involving cyanobacteria.
Daphnia galeata
water flea
Daphnia galeata is a small planktonic crustacean inhabiting freshwater lakes across the Northern Hemisphere. The species exhibits pronounced phenotypic plasticity in response to environmental conditions, particularly food availability and predation risk. Two subspecies are recognized: D. g. galeata in the Old World and D. g. mendotae in North America, with hybrid populations occurring in the lower Great Lakes. It serves as a key model organism for studying predator-induced defenses and life-history evolution in aquatic systems.
Daphniidae
water fleas
Daphniidae is a family of small freshwater crustaceans in the order Anomopoda, commonly known as water fleas. The family contains approximately 121 species across five genera: Ceriodaphnia, Daphnia, Megafenestra, Scapholeberis, and Simocephalus. Daphniidae species are important model organisms in ecology, toxicology, and evolutionary biology, particularly the genus Daphnia. Many species have been accidentally introduced to regions outside their native ranges through human activity.
Eurycercus
Eurycercus is a genus of large-bodied cladoceran crustaceans (water fleas) and the sole genus of the monotypic family Eurycercidae. Species reach up to 6 mm in length, making them among the largest anomopods. The genus contains 16 described species distributed across four subgenera, with a primarily Holarctic distribution and some extensions into the Neotropics and Southern Hemisphere. Species occupy littoral zones of freshwater lakes and ponds, often associated with submerged vegetation.
Eurycercus longirostris
Eurycercus longirostris is a Holarctic cladoceran crustacean first described by Hann in 1982. A 2011 taxonomic revision synonymized E. vernalis with E. longirostris due to lack of morphological and genetic justification for their separation. The species has a broader distributional range than previously recognized and belongs to the subgenus Eurycercus (Eurycercus). As a member of the Eurycercidae family, it shares characteristics with other chydorid-like cladocerans including a rounded carapace and specialized feeding appendages.
Holopedium
water flea
Holopedium is the sole genus in the family Holopediidae, comprising approximately seven described species of planktonic cladocerans commonly known as water fleas. These crustaceans are distinguished by a gelatinous capsule surrounding the body, which serves as an inducible defense against predation. Species within this genus exhibit notable phenotypic plasticity in body size, capsule dimensions, and reproductive investment in response to predation pressure and food availability. The genus has been studied extensively for its population dynamics, predator-prey interactions, and responses to environmental stressors in freshwater lake systems.
Ilyocryptus
water fleas
Ilyocryptus is a genus of freshwater cladocerans (water fleas) in the family Ilyocryptidae. Species in this genus are characterized by a benthic lifestyle, inhabiting lake sediments and muddy substrates. The genus has a global distribution with notable diversity in the Neotropics and Far East. Several species groups have been identified, including the widespread I. spinifer group and the sarsi-group, with some taxa showing complex biogeographic patterns across transitional zones between boreal and tropical regions.
Leptodora
Invisible Water Flea
Leptodora is a genus of large, nearly transparent predatory cladocerans containing two species: L. kindtii, widespread in temperate lakes across the Northern Hemisphere, and L. richardii, known only from eastern Russia. Adults are among the largest planktonic cladocerans, reaching up to 21 mm in length, with approximately 98% transparency as a defense against fish predation. The genus is taxonomically isolated as the sole member of its family Leptodoridae and suborder Haplopoda.
Macrothricidae
Macrothricidae is a family of small freshwater crustaceans in the order Diplostraca (formerly Anomopoda), commonly known as water fleas. The family comprises approximately 17 genera and at least 80 described species. Macrothricids exhibit diverse ecological specializations and feeding mechanisms, with many species inhabiting littoral zones of lakes and ponds. The family remains among the least studied groups of Cladocera, with ongoing taxonomic revisions revealing previously unrecognized species diversity and biogeographic patterns.
Picripleuroxus
Picripleuroxus is a genus of small freshwater cladocerans (water fleas) in the family Chydoridae. Members of this genus are benthic or epiphytic microcrustaceans inhabiting lakes and ponds. The genus was established by Frey in 1993 and is distinguished by specific morphological features of the carapace and postabdomen.
Polyphemidae
Polyphemidae is a family of predatory water fleas (Branchiopoda) containing the single genus Polyphemus with two recognized species: P. pediculus and P. exiguus. Members are characterized by large, raptorial antennae used for capturing prey and a reduced carapace that leaves the body exposed. P. pediculus has a broad Holarctic distribution in freshwater and brackish habitats, while P. exiguus is restricted to the Caspian Sea. Cryptic species have been identified within P. pediculus due to allopatric speciation.
Simocephalus
water flea
Simocephalus is a genus of freshwater cladoceran crustaceans commonly known as water fleas. Members exhibit the characteristic cladoceran life cycle with alternating parthenogenetic and sexual reproduction phases. The genus has been studied extensively for reproductive biology, with environmental factors such as temperature, food concentration, crowding, and illumination influencing life history traits.