https://www.nytimes.com/2018/02/05/science/mutant-crayfish-clones-europe.htmlThis is actually an amazing read. Some home aquarium owner in Germany noticed a pet crayfish he bought overbreeding, they ended up having way too many of them and were soon giving them away to all their friends. It turns out that a mutant crayfish was born with 3 sets of chromosomes instead of two (e.g. the parents sperm or ova didn't divide properly), e.g. the kind of thing that normally happens with plants. But somehow the extra chromosomes didn't kill it, they made them grow larger than normal and pump out absolutely massive loads of eggs, which happened to also self-fertilize, due to the extra chromosome.
So the things just pump out clones like proverbial Tribbles without needing to mate, they ended up in every pet store, and of course, some idiots eventually dumped their excess crayfish into the wild, and these oversized mutant baby-pumping crayfish are now spreading across Eurasia, even to Madagascar and Japan. Technically, they're a completely new species (since they can no longer breed with the parent species), that came into existence
instantly due to a copying error in one sperm or ova cell back in the 1990s. A whole new species coming into existence in a flash is something that's not uncommon in plants (e.g. some plant hybrids can breed with the same hybrid, but not the parent species), but I haven't heard of that in animals before.