Fairy-shrimp are temporary freshwater crustaceans adapted to very concrete conditions of the aquatic environment and with very strict tolerances to certain environmental factors and are therefore considered good ecological indicators.

They differ from the remaining Branchiopodes due to the lack of carapace. This temporary freshwater crustaceans can reach a maximum length of 3.7cm.

Crustaceans of the order Anostraca, have separated sexes but with a clear sexual dimorphism, that is, the males and the females have a different aspect. Males have retractable penis and antennas developed to grab the female during intercourse. The females have smaller antennas and have a long ventral conical ovissac that can reach the level of the 6^th abdominal segment. It is in this ovissac that the eggs mature and are stored until their release.

These temporary freshwater crustaceans live in temporary pponds with few or no predators. One very interesting feature is that these fairy-shrimp swim freely with the belly upwards throughout the water column.

Movement, respiration and feeding are done together by toracopods beating which remove particles from the water column, such as phytoplankton, protozoa, organic debris or even clay particles because they have some organic matter in their composition. These foods accumulate in the alimentary canal and are pushed to the mouth with the help of the first toracopods.

In the image it is possible to observe a Male (up) and a Female (down).

Other caracteristics are ilustrated in the next image.

Ref: Adaptado de Alonso, M.1996. Crustacea, Branchiopoda. In Fauna Ibérica (eds, Ramos, M.A., Alba, J., Bellés, X., Gonsálbes, J., Guerra, A., Macpherson, E., Martin, F., Serrano, J. & Templado, J.), 7: 1-486. Museo Nacional de Ciencias Naturales-CSIC, Madrid.