The Naruvians are a mysterious race from the planet Naru, in the Intense Universe, whose chief distinguishing feature is the ability to add, remove, or interchange body parts at will. There are friendly Naruvians and there are others (the URPS) who are, in the present era, under direction to assimilate all life forms into their collective, known as Unalon. There are at least a couple friendly Naruvians on Procyon.
Because their body parts are relatively short-lived, and thus in constant need of exchange, a Naruvian is somewhat difficult to describe in terms of appearance. The one that helped with Tommy Tomias's surgery was a patchwork of mismatched parts, while the one in Tommy's neighborhood, named Nubi Eisenpferd, looked like a slender anthropomorphic bear with an insect eye and antennae, a horse's ear, a cloven hoof for a right hand, and of course a pair of bird-like wings.
As Tommy and PJ demonstrated, Naruvian body parts may be attached temporarily to another species if they are already compatible.
If a Naruvian takes a body part from another creature by force and assimilates it, that part becomes Naruvian and adopts the Naruvian characteristic of altering the cells of adjoining parts so as to be compatible. When Ferrex of the Beastknights reclaimed his stolen arms and reattached them, they went to work on the rest of his cells. This gave him the power to reassemble his body when he was absorbed into an URPS conversion device, resulting in his complete conversion to Naruvian. While Ferrex himself appears unaffected externally, the instability of his cells may significantly shorten his lifespan.