Q:

Animal for small aquarium

I have a very very small aquarium (2L of water). What kind of animal could live in this size of aquarium with enough happinness? Maybe a starfish? Or some kind of crustacean?

A:

Frankly, nothing will be happy in such a small tank.
I don't have experience with starfish and crusacean, but a quick google search indicates that they require bigger tanks. 
If you're interested in setting up an aquarium with animals, then you'll probably need to have around 20L. Then you can start with shrimps or a single betta

