Yeah, but again, the ancestral divergence between humans and arachnids is MUCH more significant than humans and other mammals, or even reptiles in this case. If memory serves, spiders are descended from some kind of cambrian period arthropod.
Many species of monkeys have tails. Humans don't appear to. There's tons of five-limbed monkeys, yet humans only have four?! OMFG, how can this possibly be?! They're clearly related, yet five > four?!
Most mammals are covered head to toe with fur. Humans have very, very little. OMFG!
Dolphins are mammals, yet... they live in the water?! And have fins instead of arms and legs?!?! AHHHHH!!! MY BRAINZ!!!
Also, alien world with zero -- that's zip, nil, zilch, nada single bit -- of genetic information, evolutionary paths, or biological history available to the audience. Just a few random animals you
assume to be closely related to the na'vi (no matter how wrong you are) from a tiny
and completely insiginificant
sampling of that alien world.