Carcinisation (Or Carcinization for the Americans).

From reading it you might think it was related to 'carcinogen', a substance which promotes the growth of cancerous cells.... And you'd only be half right.

"Carcin-" and "cancer" are in this case linked not by chemistry, but by astrology. Carcinisation is a process of convergent evolution (that is, animals evolving independently of each other and not otherwise being genetically related) to eventually come to resemble a crab-like creature.
Apparently it's something that has happened 5 or 6 times throughout history - nature really, really likes crabs and keeps trying to get things to evolve into them from several different sources, so much so that the process has its own name.