**3. Microscopic and macroscopic biodiversity**

Hypersaline lagoons contain the three domains of life, Archaea, Bacteria, and Eukarya [29], and this section provides a glimpse to the prokaryotic and eukaryotic diversity of lagoons located at the latitudinal extremes already described. As a representative eukaryotic, the brine shrimp *Artemia* is the obvious choice taking into account its key role in the food web of hypersaline lagoons [17] and because it is a model extremophile for studies of evolution and adaptation [10, 6]. Some adaptations explain *Artemia* abundance and the ability of females to perceive forthcoming

environmental conditions. Although both domains have coexisted and evolved under similar environmental pressures, the historical trend has been to consider them independently. However, later in this chapter, the *Artemia*-bacteria (microbiota) interaction is considered as an example of a symbiotic relationship.
