I second this, 3 tentacles don't have hit boxes or collisions and my AI warthog gunners only targets the main body.

(Edit: tried it again, accidentally killed a tentacle by the downed scarab but I have no clue how that happened, hitboxes must be scuffed.)

(Edit 2: Nevermind, the last 3 tentacles appear to only be able to be killed by infantry weapons, I tried ramming them with prowlers, warthogs and choppers but I eventually used a spartan laser and that worked)