Hi Manolo:
I agree with Rick -- probably a rehilted bayonet.
When I saw your sword my first thought was the British P1856/1858 bayonet with the "button" finials on the guard. Although close, your blade has a T-spine, the fuller on your blade is wrong, and your sword seems to have a wider and less tapering blade than the British P1856 bayonet.
Unfortunately my bayonet references are buried deep in my study and I can't access them easily -- not a current passion.

But I will keep looking. In the meanwhile, here is a picture of a British P1856:
http://arms2armor.com/Bayonets/brit1856.htm
Ian.