Natural Weapons
Natural weapons (and natural attacks) such as acid spit, bite, claw, or slam don’t require ammunition and can’t be disarmed or sundered.
In addition, a player character with this ability can attack with a special unarmed strike that deals lethal damage, doesn’t count as archaic, and threatens squares. They also gain a special version of the Weapon Specialization feat with this unarmed strike at 3rd level, allowing them to add 1–1/2 × their character level to their damage rolls for this unarmed strike (instead of just adding their character level as usual).
Source
Alien Archive pg. 155