Brine Shrimp
(Artemia sp.)

"Sea monkeys" are actually brine shrimp, and are also called fairy shrimp. They are crustaceans, and thus related to lobsters and crabs. Their life cycle can include a step in which they form a hardy embryonic cyst in harsh conditions. This state is called diapause. The cyst is reactivated when re-exposed to water, hence "sea monkeys" can be hatched from stuff that can be mailed to you. Most claims about "sea monkeys" are sort of blown out of proportion (doing tricks, resembling those pink things in the ads...) but Artemia has been studied extensively regarding water balance. They can tolerate salinities from 10% sea water to the saturation point for NaCl. (The "magic crystals" are probably just salt...) This is why they are called brine shrimp, and can live in places like Utah's Great Salt Lake. Their internal osmotic pressure varies only slightly with external conditions. Ionic regulation is maintained by absorption or excretion of salts through gills. They can also excrete hyperosmotic urine (in reference to its blood), with the osmotic pressure of the urine being 4 times that of the blood. Identifying characteristics are a trunk composed of 11-18 segments with appendages, no carapace, and eyes compound and stalked