We have several for animal ears or tails, one for horns and another for antlers, and several for wings, but none to my knowledge for tentacled humanoids. If we have one, please tell me and then ignore this thread. If we don't, then let's make one.
The distinction between the organ when on a humanoid isn't important for horns, wings, or antlers because those tags are mostly used for the appendage as attached to humanoids in the first place, but with tentacles, we probably have more images where the tentacles are attached to a monster of some sort than images where the tentacles are attached to a person.
We do, however, already have tentacle_hair, which should probably implicate this.