For example, many hermit crabs have a soft, asymmetrical coiled hindbody that allows them to fit into the right-handed twisted shells of their mobile homes. In the evolution of the king crab, this hindbody has become shortened and folded flat under the front part of the body. Nevertheless, traces of this asymmetry can be seen in the king crab hindbody. Furthermore, asymmetric hermit crabs usually have a larger right claw, as do king crabs.

We can also better picture how a shell-toting hermit ancestor eventually gave rise to large free-living king crab by considering the lifestyle of the coconut crab. This species can reach up to 9 pounds and is the largest land-dwelling arthropod. In fact, it is a member of the hermit crab superfamily. While the adult crabs are free-living and hard-bodied, juvenile coconut crabs have a soft hindbody and live within the snail shells. The two life stages of this one species demonstrate that the shift from shell-toting hermit to large king would not be as complicated as it might first appear.

Another well-established example of deceptive looks in the animal kingdom involves the rock hyrax, elephant and manatee. Glancing at the modern forms of these mammals, one would hardly suspect that they are very closely related. The hyrax, weighing 8 to 10 pounds and resembling a guinea pig, lives among rock crevices in Africa and parts of the Middle East. It hardly seems possible that is could be close kin to the 10,000-pound, trunk-swinging African elephant or the aquatic manatee.

But again, DNA evidence makes it crystal clear that these species, which belong to three different orders, all belong to one larger group known as the Paenungulata that arose from a common ancestor that lived in Africa roughly 60 million years ago. Each group — the hyraxes, the sirenians (manatees and dugongs) and the elephants, is the other groups’ closest living relatives.

Those close relationships are also reflected in specific features of the animals’ anatomies and behavior. For example, if one looked closely at males for their testicles (not that I recommend doing so, particularly for elephants), one would not find them. The testes are inside the abdomen in each group. The animals also share common details in their tongues, hooves and some skeletal features. In addition, all have very long gestation periods; the hyrax’s is seven to eight months, which is exceptional for a relatively small mammal.

While the evolutionary relationships here are surprising, it should be no surprise that the first naturalist to appreciate how looks could trick us was Charles Darwin. One stroke of his genius in “On the Origin of Species” was to begin the book with a discussion of domesticated animals, like the pigeons he had bred for many years.