Vestigial Arm and Monstrous Extremities

[Cao Phen]

Vestigial Arm wrote:

The alchemist gains a new arm (left or right) on his torso. The arm is fully under his control and cannot be concealed except with magic or bulky clothing. The arm does not give the alchemist any extra attacks or actions per round, though the arm can wield a weapon and make attacks as part of the alchemist’s attack routine (using two-weapon fighting). The arm can manipulate or hold items as well as the alchemist’s original arms (for example, allowing the alchemist to use one hand to wield a weapon, another hand to hold a potion, and the third hand to throw a bomb). The arm has its own “hand” and “ring” magic item slots (though the alchemist can still only wear two rings and two hand magic items at a time). An alchemist may take this discovery up to two times.

Monstrous Extremities wrote:

You change one of the extremities of the creature touched—arms or legs only—into another shape of approximately the same size and mass. You can choose a tentacle, a hoof, or a wing. The subject must take approximately 10 minutes to familiarize itself with the function and movement of the new extremity to use it properly. These new forms do not allow the subject to fly, run faster, or swim better; however, they do act as natural weapons of the appropriate type, and the subject can use them to make secondary attacks while making attacks with weapons as a full-attack action. The secondary attacks are made using the creature’s base attack bonus –5 and adding only 1/2 the creature’s Strength bonus on damage rolls. The subject cannot hold a weapon or use any item that would ordinarily fit into the slot of the changed extremity. The subject can receive the benefits of this spell multiple times.

With that, can you use the Monstrous Extremities spell on the Vestigial Arm to for it to gain an attack?

[Firebug]

Monstrous Extremities is a Polymorph subschool spell.

As such:

Polymorph Subschool wrote:

While under the effects of a polymorph spell, you lose all extraordinary and supernatural abilities that depend on your original form (such as keen senses, scent, and darkvision), as well as any natural attacks and movement types possessed by your original form. You also lose any class features that depend upon form, but those that allow you to add features (such as sorcerers that can grow claws) still function.

You would lose the Vestigial Arm when you cast Monstrous Extremities. Even if you were transforming your legs.

Monstrous Extremities should not have the Polymorph subschool. In the description of the subschool every Polymorph spell should contain a creature that you can shift into. Monstrous Extremities does not. This breaks a few things, like the fact that without a creature listed in spell description you lose all of your senses. Normal limbs would also be gone among other things.

Regardless, my Alchemist character is not happy about this. Essentially for 2 level 2 slots, my shield arm, Darkvision, Cold/Electric/Acid resist 5, I get 2 secondary natural attacks. Not a good trade.