You have one less arm than other members of your species. This makes it more difficult, or even impossible, to do things that require the regular number of arms or hands for someone of your species. You suffer a 1D+0 penalty to any action which is normally performed with the full complement of arms or hands, and at the GM’s discretion certain activities may be impossible for you to attempt.
You may buy out this disadvantage for 30CP, if you wish to replace your missing arm with a prosthetic, or if you have found a suitable donor and a doctor willing to stitch you and your freshly harvested arm together.