No one knows I guess... but here is a quote from Badflash with a possible answer

These are an interesting breed, sort of a frankenfish. No one knows where they came from, but the conventional wisdom is that they came from an accidental hybridization between two different species of north American crayfish.

Marmorkrebs are the only known species of crayfish that are all female. Each female is identical to the mother and she produces fertile eggs without mating.