How to detect a 'transformed' unit ?

For morphing spells like metaphorphosis and bear form, I want to know the relationship between the morphed form and the orignal.

Say I want to create special effects or disabling/removing abilities from that transformed unit, how shall I call it with triggers? I've tried 'Triggering Unit' or 'Unit enters region' triggers but they don't work. So I wish to how are there any ways to detect the morphed unit by triggers so I can do something to it.

Thanks.

i have a trigger like

trigg1
unit starts the effect of an ability
ability equal to morphspell
set morphunit = triggering unit
remove ability X from triggering unit
enable trigg2
wait 45 game secs
disable trigg2
give ability X to triggering unit

trigg2
every 1 gameseconds
remove ability X from morph unit


u need trigg2 cause of:
if the hero LEARNS a new skill, he will get the ability again, even if u removed it..

You might also want to look at Disabling the ability for the Owning Player. I'm using this in a map I'm working on, and even if the hero gains a level he can't put a point into the disabled skill untill it is Enabled again.

Of course, this would disable it for all units that the player owns. Not usually a problem for hero skills since the same skill rarely appears on two heroes owned by the same player.