Animals have evolved into a crab-like-shape at least 5 separate times

Evolutionary biologist L. A. Borradaile once defined carcinisation as, "one of the many attempts of Nature to evolve a crab."

According to a 2017 paper from the Biological Journal of the Linnean Society, this evolutionary process has occurred on at least 5 separate occasions in the last century alone:

Curiously, not only did the crab-like habitus evolve independently from the 'true' crabs (Brachyura), it also evolved three times independently within anomurans.