Ecology experiment - suggestions ?

I'm going to try the ecosphere idea again, and I'd like some suggestions, or
corrections if anything written here is a bad idea.

I plan to use an old gallon jar ( 3.8 liters) with a tight-fitting lid, a
cup of pond mud, a cup of used aquarium gravel, about a dozen leaves of
duckweed ( Lemna minor) , a small Hygrophila plant, a small Anacharis plant
, some small bits of algae, some copepods, 3 small snails, and 3 ghost
shrimp. I plan to leave about 1/2 a liter of air in the top when I seal the
jar. The room temperature is a constant 72 to 77 F , and the jar will be
placed next to a west-facing window.

Any species I should add or leave out ?
Anything here sound like a problem ?
Any other ideas ?

Limnophile