Iguana is Leguan in German. How come?
The word reflects in both cases Spanish iguana, which is taken from an indigenous South American language – the initial „L“ is from the Spanish article: la iguana was rendered (the) leguana by the Dutch who brought it to the old continent.
This process is called rebracketing – Wikipedia has more examples. Funnily, there’s more reptiles whose names were affected by that same process:
A nadder is eine Natter in German. This time English has reinterpreted the word boundaries: an adder > a nadder
Alligator comes from Spanish el lagarto. English has done the remodeling and passed the word on (back to Spanish as well).