The tentacles are uniform in Mags, they can bubble or taper (almost come to a point) at the ends in a bubble tip.
The oral disc in H. mag is about the same size as the foot. its almost like one giant column with tentacles. Where as bubble tips have a much narrower foot that it likes to hide between rocks. The foot in H mag. is normally prominent if viewed from a horizontal plane.
The mouth on the H. Mag protrudes, like a nipple in shape. The BTA mouth is normally just a closed slit in the oral disc. The mouth appears smooth. But this isn't always that helpful to me because the mouth never looks normal unless the specimen is very healthy.
Bring back more pics!