I'm pretty sure the Zuma are the result of the leg's coming back to life and growing new bodily features aftering being severed at the command of Duke Hrok in Solaria. Not only do they become gruesome beasts but they retroactively became the Zuma before the legs were even cut off in the first place.
Therefore, the Zuma are simply a result of a Duke getting pissed off and taking it out on couriers.
