Classification: electrophone?

Under musical instrument classification, is a theremin considered an electrophone?  This seems to be the case using Hornbostel-Sachs system.  Is there a further subcategory under that system, or is that it? electrophone>theremin

Is there another subcategory of instruments it falls under using another classification system? Perhaps just considered a type of electronic musical instrument and that's it?

I think this answers the question:

http://en.wikipedia.org/wiki/Electrophone

The electrophone category was added to the Hornbostel-Sachs musical instrument classification system by Sachs in 1940, to describe instruments involving electricity. Sachs divided his 5th category into 3 subcategories:

• 51=electrically actuated acoustic instruments (e.g., pipe organ with electronic tracker action)
• 52=electrically amplified acoustic instruments (e.g., acoustic guitar with pickup)
• 53=instruments which make sound primarily by way of electrically driven oscillators

The last category includes instruments such as theremins or synthesizers, which he called radioelectric instruments.