Does anyone know why an echidna is so named?

Easy variant: Does anyone know what an echidna looks like? Yes, that was easy, it looks exactly like a hedgehog. Here are some things it looks nothing at all like: a camel, a crab, a viper, a horse.

What is the Greek for 'hedgehog'? It's echinos. What is the word right next to that in a Greek dictionary? It's echidna, which means 'viper'.

What is my theory? That some enthusiastic junior zoologist in the 1820s with small Greek got it wrong and they've been covering up for him ever since.