"Secondary" Natural Attack of Opportunity

[Criik]

My alchemist has the tentacle discovery.

Spoiler:

The alchemist gains a prehensile, arm-length tentacle on his body. The tentacle is fully under his control and cannot be concealed except with magic or bulky clothing. The tentacle does not give the alchemist any extra attacks or actions per round, though he can use it to make a tentacle attack (1d4 damage for a Medium alchemist, 1d3 damage for a Small one) with the grab ability. The tentacle can manipulate or hold items as well as the alchemist’s original arms can (for example, allowing the alchemist to use one hand to wield a weapon, the tentacle to hold a potion, and the third hand to throw a bomb). Unlike an arm, the tentacle has no magic item slots.

Note that the tentacle does not give extra attacks, but can be used in place of a normal attack. A tentacle is normally considered a secondary attack per the natural attack chart. However, the tentacle discovery does not grant it as a secondary natural, and is only used in place of another attack. If I use it as an Attack of Opportunity, do I apply the penalties normally applied to secondary attacks (-5 to hit, x.5 strength bonus)? Or would it receive normal full attack bonus, x1 strength for its attack?

[Avianfoo]

There is also the rule that states if a creature has only one natural attack (or multiple of the same type) it is a primary attack.

The alchemists tentacle attack is rather limited and can be used as his only attack... so it would be a primary attack, in my mind. Though I am suddenly unsure if it gets x1.5 Str mod or the normal x1.0 Str mod.

[Criik]

Well, it is not the only natural attack that my alchemist has. He also tends to have the Gore from Helm of the Mammoth Lords, and his 2 claws and a bite from Feral Mutagen. However, on an AoO, only the one attack can be utilized. This same question would also be applicable when limited to just a standard action. If I only use the tentacle attack (in place of my monk enabled unarmed strike), is this a full attack bonus attack?

[SlimGauge]

Criik wrote:

However, on an AoO, only the one attack can be utilized. This same question would also be applicable when limited to just a standard action. If I only use the tentacle attack (in place of my monk enabled unarmed strike), is this a full attack bonus attack?

This is HAVE vs CAN USE. It doesn't matter how many you USE, what matters is how many you HAVE. If you HAVE gore, two claws, a bite and a tentacle but only USE the tentacle, if the tentacle isn't already a primary attack it doesn't get bumped up to one.