Matryomin is a matryoshka-shaped theremin invented by Masami Takeuchi, who studied in Russia with a relative of Lev Termen, who had started it all. Matryomin has a good property of pitch, similar to a real theremin, five octaves wide. It is handy to prepare playing the real theremin, and eminently suitable for ensemble playing because its electromagnetic field is smaller than that of a theremin.
Take a look at the website, but even better, watch how to tune and play the instrument, and better yet, observe 167 automaton-like Matryomin fans perform Beethoven’s Ninth Symphony in unison. Thanks to Garry Margolis for pricing the instrument, in case you want to join the band: from the company in Japan, $420; from Amazon, $650 — but Amazon makes returns easier than the Japanese manufacturer.