B422 describes penalties but there isn't really a trait to go with them...
- If a tail counts as an Extra Arm or a Striker, or is a fish tail, treat it as a limb (arm, leg) for crippling purposes; otherwise, treat it as an extremity (hand, foot). A crippled tail affects balance. For a ground creature, this gives -1 DX. For a swimmer or flyer, this gives -2 DX and halves Move. If the creature has no tail, or a very short one (like a rabbit), treat as “torso.”
A tail (or a rudder, or a similar stabilizer) is assumed if you take Flight with the Winged limitation (p. B56) or No Legs (Aquatic) (p. B145).