How does the rudra veena differ from the Saraswati veena?

The rudra veena of Hindustani music is a stick zither: a hollow tube with two large gourd resonators beneath it. The Saraswati veena of Carnatic music is a long-necked lute with fixed frets, its 24 frets set into a ridge of beeswax on the neck. The rudra veena is closely associated with dhrupad and is plucked with a wire plectrum on metal frets.