Biologists have been observing a strange process that has been dubbed "craification" for many years. This is the process of evolution of a wide variety of crustacean groups into crabs - and it has already happened five times in completely different contexts.
What is the essence of krabification? Animals living in similar conditions face various difficulties that push them to acquire similar evolutionary advantages. Thus, different animals can evolve independently of each other, but move in their development towards a specific, most optimal form. Or, for example, spontaneously acquire similar characteristics, being in completely different groups. Birds and bats can fly using mechanical wings, but they are completely different species. Birds and mammals are warm-blooded, but both descended from other groups of creatures that were cold-blooded.
Different crabs, in turn, acquired the same specific shape independently of each other, which is very unusual. They have been compared to the Galapagos birds studied by Charles Darwin. But crabs developed specific characteristics spontaneously, rather than under the pressure of isolation and specialization, as was the case with the Galapagos finches. Moreover, all five cases of crustacean crabification are united not only by the body shape acquired by animals, but also by the structure of the nervous and circulatory systems and many other parameters.
An article dedicated to a century of observation of the crabification process was published in the Biological Journal of the Linnean Society, University of Oxford.