Decorator crabs weave leaves of seaweed, as well as sponges and anemones and other marine organisms, onto themselves as an extension of their "skin", which camouflages and protects from predators. Surely they must be human!

(I almost feel as if you and I were Plato and Diogenes discoursing on the definition of a human being. Plato defined humans as "featherless bipeds", Diogenes quickly ran to the market and purchased a roast chicken - which had two legs and no feathers - which he brought before Plato, who then added "with broad fingernails" or something.)