Brine shrimp are also not shrimp, but they do belong to the same group, the crustaceans. They are tiny, just 15mm long. They eat algae, which they filter out of the water. They swim upside-down and breathe through their legs, and females do not need a male to reproduce.
Crucially, they have a unique affinity for salt. They can tolerate concentrations up to 50%. Such water is far saltier than the ocean, which is only about 3.5% salt, and the salt will be on the verge of precipitating out as a solid.