Creating 'tentacle' effect?

I am looking to create a ‘tentacle’ like effect for a flash animation. A frame by frame animation is not ideal as it is arduous and not very easily manipulated.

I have attached an fla of the effect I am looking for. Ideally it would be a line that snakes in and grows thicker at the back end. I can create it in the way included in the fla but it is not very portable and i cannot overlay different tentacles.

I think that a layer mask would be good but I cannot think of a way to go about it.

Does anybody have any suggestions?