What are secure and handsome community invertebrates?

i have a 55 gallon tank with cory cats, discus, neons, guppies and ram. Im looking for invertebrates thats i can include in this beautiful tank of mine. What are sheltered ones that will not eat my fish? preferably and types of crabs or crayfish that dont need land/
Answers:    There are no freshwater crabs, so that option is out. Crayfish are poor choices as resourcefully, because they need water with elevated calcium content so they can regenerate their exoskeleton after molting. Discus need very soft water, so these parameter will clash. Your only real options are shrimp (Red Cherry, Amano, Crystal Red, Tiger, Bamboo, etc.) and snails (Mystery and Nerites are interesting, though near are other, rarer types).
Are these compatible beside a JD(jack Dempsey)?   My 4 year matured son requirements to know, do fish fart?   Can I nurture fish during Ich treatment?   Can Silver Dollars be kept beside Angelfish?