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Daphnia is a genus of small planktonic crustaceans, 0.2–6.0 mm (0.01–0.24 in) in length. Daphnia are members of the order Anomopoda , and are one of the several small aquatic crustaceans commonly called water fleas because their saltatory swimming style resembles the movements of fleas .
Daphnia studeri is a species of microcrustacean in the genus Daphnia. D. studeri lives in oligotrophic freshwater and slightly brackish lakes in Antarctica and sub-Antarctic islands. Adult Daphnia studeri are typically 1.5 to 2.5 mm (0.059 to 0.098 in) [ 1 ] and colorless or slightly pink.
Daphnia magna is a typical water flea of the genus Daphnia. The females reach up to 5 mm in size, the males about 2 mm, thus they are among the largest species in the genus. [ 2 ] The body is protected by a translucent carapace made of chitin , a transparent polysaccharide. [ 3 ]
Like all Daphnia species, D. longispina is a filter feeder, collecting particles of about 2 to 40 μm suspended in the water. [5] The main food are green algae. At 20 °C maturity is reached within about 6 to 12 days, followed by a period of regular reproduction in about 3-4 day intervals.
English: Female Daphnia longispina with a clutch of asexual (parthenogenetic) eggs. The animal is about 2.2 mm long. Picture from wild caught female from rock pol in south-Western Finland. Picture by Dieter Ebert.
The switch between sexuality and parthenogenesis in such species may be triggered by the season (aphid, some gall wasps), or by a lack of males or by conditions that favour rapid population growth (rotifers and cladocerans like Daphnia). In these species asexual reproduction occurs either in summer (aphids) or as long as conditions are favourable.
Daphnia lumholtzi is typically found in the warm, shallow regions [6] of bodies of water with larger surface areas. [7] While most species of Daphnia see high mortality at temperatures greater than 25 °C, [8] D. lumholtzi individuals can survive and reproduce at temperatures up to 30 °C, [8] [9] [10] with a thermal optimum occurring at 29 °C. [9]
Resting egg pouch (ephippium) and the juvenile daphnid that just hatched from it Female Daphnia longispina carrying a resting egg (ephippium). The two dark, oval spots on the ephippium mark the places where the two resting eggs are located. The female was collected in a rock pool in south-western Finland.