You miss the point of the cartoon. It's a memory hook combined with a joke so that you can memorize the name of the animal more easily. It says: learn german. Not: Check out the etymology of the word 'Schildkröte'.

This is the most German post. You misunderstanding the joke elevated it. "The joke is factually incorrect, as the shell is the shield in the word. Your extra shield is superfluous." Meanwhile the artist: "Haha shield toad, I'll give him a shield cus its cute"