Crayfish (Procambarus clarkii), which is related to Procambarus fallax.
In 2003, biologists reported that a female crayfish, living by herself in an aquarium, repeatedly laid eggs that developed into offspring. The scientists examined her carefully for sperm or even any male gonads that might have been hidden in her body cavity, thus letting her fertilize her own eggs, as happens in some crustaceans. But no cigar. The marmorkrebs, which first surface in the aquarium trade in Germany in the mid-1990s, was simply reproducing without male help, creating a series of all-female clones of itself.
The explanation is a process called apomitotic parthenogenesis, which involves skipping a step in early egg development. Instead of dividing so that they carry half the required number of chromosomes—with the missing ones supplied by the sperm—these crayfishes’ eggs stay whole and develop into little Marmokrebs directly.
Later research suggests that the marmorkrebs is an asexually reproducing form of the crayfish Procambarus fallax, which handles its baby-making in the ordinary way. How and why the asexually reproducing form arose is still a mystery. What’s certain is that with the critter now popular among aquarium owners worldwide, it pays to have plenty of scuttling room in your tank. Even if you buy just one marmokrebs, you’ll wind up with more.