Oi, hey Rams, and Em! And Stullion! And... and Uncle Francis, the famous ivy tamer!
I had a 5 gallon I was trying to raise a copepod / daphnia culture in to use as live food, but I was actually having better luck just with jars on the windowsill, so I was cleaning it out the other day to turn it into a spare tank for rearing fry or to use as a quarantine, and found a half grown cherry shrimp crawling in the detritus on the bottom. No clue how it got there. It is right next to the shrimp tank, but that tank has a glass lid on it and I've never transferred anything between the two. I have to assume it crawled out and managed to make it to the other tank.
I tried to keep a container of daphnia once. It all died out after a couple of months. Now that I don't need it however I have it living in one of my shrimp tanks.