An aquatic ecosystem in a sealed glass bubble

We had one of these in the MAKE magazine office for years. I think the shrimp's name was Fred. Amazon has the small one on sale for $44, which is an all-time low price.

EcoSphere is a completely closed, balanced, glass ecosystem. Inside each EcoSphere are shrimp, algae, and microorganisms in salt water. Because the EcoSphere contains everything it needs to thrive, you never have to feed the life within, or change the water. All that is needed is a comfortable room temperature (between 65 and 80 F) and a source of light.