Depending on where you live there are also critters like fairy shrimp, caddis fly larvae, mussels, clams, other nymphs etc. You mighy also consider some to the native salamanders etc. I know they aren't inverts but, they are still pretty neat.
hth
and let us know what you plan to do .
max
our crays are HUGE. i had one that made lunch out of a healthy 8 inch bluegill and attacked my largemouth bass. theres no way i could keep one of those.
We have a number of varieties of crays where I live. I wouldn't worry too much about some of the dwarf crays. Most of them won't bother much at all in your tank except for maybe the snails and sick fish etc. Some of them only get an inch or two long.
hth
Max
I have caught grass shrimp, arrow shrimp, snails, hermit crabs, and other small shrimps in our local estuary. Also caught an adult spider crab, it was AWESOME, but not small. These are all brackish species.