It's weird to think there are creatures and animals on this Earth that we may have never seen before. But honestly, it's sso very likely that you don't know all the living on this mysterious planet. There's no way to really know because some creatures (such as in the deep blue ocean) have YET to be discovered!
So, the idea of there being living things we haven't seen before isn't so far fetched. Yet, it's always surprising when you see a land animal for the first time. We've never heard of a humphead parrotfish or a worm-eating giant snail before. Amazing how much there is to learn and to see, it's never-ending.