I’ve long held a gripe about science-fiction aliens: they’re always far too unimaginative. I know it’s because SF is rarely about real aliens but is always about ourselves (and is also usually but keeping the budget manageable, in the case of SF movies), but still…the model is always our species, and they can’t even broaden their horizons enough to look at the diversity within the phylum Chordata, let alone examine some of the weirdness in other phyla. And, of course, any alien life form isn’t even going to be at all related to us, so it should be even stranger. Avatar was just the worst example of this trend — and Cameron did not have the budget excuse — but Star Trek and Star Wars were also pretty feeble in biological creativity department.
Examples that buck the trend are rare. District 9 at least modeled their aliens after cockroaches. Babylon 5 had most of their primary interacting alien races boringly humanoid, but had a few oddballs lurking mostly offscreen.