Despite what you were shown on the box, sea monkeys, or brine shrimp, are female. They reproduce asexually for the most part, and their offspring are also female. They are not the only species to reproduce asexually (about one in 10,000 animal species is male-free), but brine shrimp are unique: among the vast swarms of females, you'll find a rare male.
The males were exceedingly rare–around one in thousand in many cases, and around one in a hundred in a few. And yet they were healthy and fertile. The males couldn’t mate with females of their own population, but they readily had sex with other species. What’s more, their hybrid offspring were healthy and fertile, too.
If asexual animal species are rare, species with asexual females and rare males are even more rare. Only a few other examples have turned up, such as certain populations of snails in New Zealand. Maccari and her colleagues don’t think there’s a clear answer to why these rare males exist. But there are a few plausible possibilities.
Carl Zimmer presents a few possible reasons for the discrepancy -and they are all weird. Link