Water flea
(about 14 specie in Swedish waters)


Distribution in scandinavian waters

Maximum length: 0,6 cm. Compare with the size of a hair.
Appearance: The water fleas body is covered by a two flapped shell that creates an opening on the underside. The two quite complex eyes have grown together. The second pair of antennae are large and are used to swim. The head is large, and the rostrum is pointed and powerful. There is also a point on the shells upper side. Compare the water flea with the cladocerans of the Evadne and the Podon families.
Depth: From sea-level and a few metres deep.
Environment: Water fleas are mainly freshwater organisms, but a few specie tolerate brackish water. Because of this they are found in rock pools close to the sea and in relatively closed seas with a large run-off of freshwater, for example the northern reaches of the Baltic.
Misc: Water fleas eat small organisms and other particles in the water. In turn they themselves are often eaten by larger creatures, for example, fish. With some females the young water fleas develope in the ovary without being fertilized. Several generations with only females can occur and multiply themselves partenogenetically. When harsher conditions prevail even males and certain females whose eggs were fertilized hatch. The ovaries are released when sloughing takes place or when there is a drought and are spread over large areas by the wind. Water fleas exist globally.
Classification: Water fleas are cladocerans, which are crustaceans under the arthropods. Daphnia longispina is pictured above.

Water flea    Other names

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Bo Johannesson | Martin Larsvik | Lars-Ove Loo | Helena Samuelsson