"Sea-Monkeys are a hybrid of Artemia salina, a species of brine shrimp. These are a type of fairy shrimp -- not true shrimp, but a branchiopod. The term Sea-Monkeys (sometimes unhyphenated) is a trademark used to sell them as a novelty gift. They originate in salt lakes and salt evaporation flats."
"The key observation that allowed unhatched "Sea-Monkeys" to be cheaply packaged, shipped, and handled is that in certain easily-prepared environments they enter cryptobiosis, a natural state of suspended animation. When released into their aquarium they leave this state and hatch."
Sea Monkey Wiki