what inverts will survive and possibly breed in an outdoor pond that reaches 30 degrees to 80 degrees farenheight. has koi and goldfish at the moment and japanese trapdoor snails. Thanks for any suggestions.
The other snail would be Pomacea canaliculata but I would advise against mixing them with Viviparus malleatus as canas aggressively consume anything and can easily displace other species of snails. Canas are pretty tolerant of cold temperatures and can hibernate in the process at the bottom of the pond. Only legal way of obtaining them is from a hobbyist within your state.
How about Gammarus sp? They are pretty small and will just be a food source for your fish. They are probably the size of this - "O" all curled up and look like a miniature shrimp or a small pill bug. They're not big enough to observe though lol.