It sounds like you’re looking for the filter manipulations as described here:
https://forum.inaturalist.org/t/how-to-use-inaturalists-search-urls-wiki/63
This is possible:
https://www.inaturalist.org/observations?place_id=any&taxon_ids=130868,48824
Also possible.
https://www.inaturalist.org/observations?place_id=any&taxon_id=47126&without_taxon_id=311249
Because these are not monophyletic groups this would have to be assigned to individual species/groups which would get very complicated, especially with how to define brackish, amphibious, etc.
A good approximation for mollusks would be to exclude Stylommatophora:
https://www.inaturalist.org/observations?place_id=any&taxon_id=47115&without_taxon_id=47485
I suppose you could exclude spiders from all of your searches but that might be a bit of a pain.
You can create a place by uploading a polygon you have drawn, and then you can search within that place.