Bandoneon, concertina or Bandonika?
A rectangular instrument may be a bandoneon, a German concertina or a Bandonika.
Bandonika
The Bandonika is essentially a diatonic accordion built in the shape of a bandoneon. It can be recognised by the relatively small number of bass buttons, some of which produce complete chords.
German concertina
The concertina and the bandoneon have essentially the same origins. As more notes were added, however, their keyboard arrangements developed in different directions.
Concertinas tend to have fewer but longer rows, while bandoneons generally have more rows with fewer buttons. Concertinas also use different layouts, including the Chemnitz and Carlsfeld systems.
The Chemnitz concertina is still widespread in the Midwestern United States.
Bandoneon
If the instrument is neither a Bandonika nor a concertina, it is probably a bandoneon. But bandoneons also exist in many different forms.
