convergent evolution

This process of carcinisation is a form of convergent evolution.

"The convergent evolution of crabs has happened about five times in history, but it's happened within the group of decapods."

This makes them striking examples of convergent evolution, where two evolutionarily distinct groups evolve similar characteristics due to similar environments and occupying similar niches.

This is the same process that occurs over tens of thousands, even millions of years in living creatures, from slugs to dogs to you and me, producing the incredible diversity we see in the tree of life along with startling replays of the same idea, known formally as convergent evolution.

Convergent evolution is what we see when we observe that bats and birds have similar development of their arms into gliding wings, which initially allowed them to glide, and then to fly.