Extra Legs is an exotic physical advantage described on B54
Enhancements: Long, all legs (+100% per +1 to SM)
Limitations: Cannot Kick, all legs (-50%)
http://forums.sjgames.com/showthread.php?t=10110 PK mentions that B55's "Modifying Beings with Two Legs" rules ought to use 1/20 of % in points instead of 1/10. Such as coming up with a Long Legs advantage or Cannot Kick disadvantage.