My GM has made a ruling and I've no intention of making a fuss in his game if he turns out to be mistaken, but the wording is vague enough that I'm curious and I'd like to know for future games.
Is there an official answer on whether or not grasping tentacles deals damage?
The spells
Grasping Tentacles:
This spell functions as black tentacles, except the tentacles blindly grasp at the targets’ eyes and ears, and tug at their hair, clothes, and equipment. Instead of grapple attempts, the tentacles attempt dirty trick combat maneuver checks (CMB = your caster level + 4 [the tentacles’ Strength bonus] + 1 [the tentacles’ size bonus]). Roll on the following table to determine the effect of a successful dirty trick combat maneuver check.
Black Tentacles:
If the tentacles succeed in grappling a foe, that foe takes 1d6+4 points of damage and gains the grappled condition. Grappled opponents cannot move without first breaking the grapple. All other movement is prohibited unless the creature breaks the grapple first. The black tentacles spell receives a +5 bonus on grapple checks made against opponents it is already grappling, but cannot move foes or pin foes. Each round that black tentacles succeeds on a grapple check, it deals an additional 1d6+4 points of damage.
The Confusion:
So grasping tentacles functions as black tentacles, except doing dirty tricks. Black tentacles deal damage upon successful grapple checks. So does that mean Grasping deal damage upon successful dirty tricks?
Black tentacles also says that targets can't move while grappled, but obviously that isn't the case with grasping tentacles preventing movement while dirty tricked (unless it's entangled) so it's obviously not a simple case of "replace all instances of 'grapple' with 'dirty trick' and I can personally see valid arguments for both sides.
No. Black Tentacles does NOTHING if they fail the grapple check. If they succeed at a GRAPPLE CMB check, they do damage and the target cannot move.
Grasping Tentacles never makes a GRAPPLE CMB check so it never does damage and never prevents movement. Instead, it makes a DIRTY TRICKS CMB check and then does whatever is rolled on the table. No more.
That's why it's a lower level. If it did what Black Tentacles does, AND added a condition too, it would be higher level.