This tiny organism is called a Daphnia magna, and as observed you can see the eggs it contains with it.
This creature is between 0.2 mm to 5mm, that is 0.5 cm. I never knew anything about the Daphnia until Biology. Moreover, this is related to caffeine, which is related to your high blood pressure and a major cause of heart attack. No, you don't eat it, and even if you do you won't get a heart attack. Foolish Manal.
It can die with 1% caffeine concentration in a solution. Top that, you can see it's heart contract and relax when focused on a microscope. Either the heart or you can see the legs beat, and so you can see it's rate of heart beat. Amazingly, this tiny creature is vulnerable to extinction in the wild- threatened. Some of them are unsurprisingly extremophiles, but the bad news is that even these are under threat.
It looks so motherly, which reminds me I have a Biology Premock to solve. =)