Reproductive arrangements don't get much stranger than those of the Batura toad of Pakistan. The entire species is the result of two unknown species interbreeding, and each toad carries three sets of genes...which makes passing on its genome extremely tricky.
The predator-prey relationship between frogs and beetles seems like it would be pretty obvious doesn't it? Frog spots beetle, frog stealthily approaches beetle, frog eats beetle. Done, done and done.