Note that it's not a centipede. Because wearing shoes is the hardest, not the longest. Centipede's feet are very simple if you design a shoe.

First of all, the most difficult animal to wear shoes must have more complicated or strange feet than ordinary animals.

Followed by snakes, snail slugs and so on. It is not enough, so it should be ruled out.

Finally, I finally came up with an animal that is difficult to wear shoes, but not necessarily the most difficult, and that is jellyfish.

Because jellyfish's feet (that is, tentacles) are thin and soft. The essence of shoes is comfort and fit. So shoes must also be thin. But it's hard to wear shoes. Jellyfish have receptors on their tentacles. When the tentacles of jellyfish come into contact with small fish, they will produce nerve impulses, release venom and entangle it. In the process of swimming, jellyfish usually drift with the tide, because jellyfish tentacles have few muscles and will not do other actions during swimming. So if a jellyfish sticks its tentacles into a shoe as thin as a thread. That's impossible. It's hard.

So the hardest animal to wear shoes in the world is jellyfish.