I beg to differ: (edit2)tentacle with mouth is distinct that the tentacle itself has a mouth, not the other way around. Further, tentacle in mouth and mouth tentacles have their own distinctions, and their purposes are not ambiguous at all.
...Although I can agree, perhaps they can be worded differently/more accurately with each other.
(edit) I will be against the deprecation of one of either instead of aliasing one or the other, because that would reduce the chance of avoiding ambiguity.
These are just under-utilized since I think there are only a few people concerned with or looking for tentacle specifics, so I don't regard the number of posts in it much.
mouth tentacles - tentacles seen emerging from the mouth, like having multiple tongues but could be ambiguous to it if it doesn't have any monstrous look/has the common nondescript tentacle look.