A Chemnitzer concertina is a musical instrument of the hand-held bellows-driven free-reed category, sometimes called squeezeboxes. The Chemnitzer concertina is most closely related to the bandoneón, and more distantly, to the other types of concertinas and accordions. It's essentially a bigger version of the Anglo Concertina that sounds more akin to an Accordion due to having Multiple Ranks of Reeds.
Chemnitzer concertina
"Pearl Queen" 39-button model (Serial Number : 3762, Manufacture Year : 1926)
"Pearl Queen", Anglo concertina, bandoneon
Supreme Chemnitzer Concertina
The bandoneon is a type of concertina particularly popular in Argentina and Uruguay. It is a typical instrument in most tango ensembles. As with other members of the concertina family, it is held between the hands, and played by pulling and pushing air through bellows, routing it through sets of tuned metal reeds by pressing the instrument's buttons. Unlike most accordions, bandoneons always employ the same sets of reeds to produce their sound, and do not usually have the register switches common on accordions. Nevertheless, the bandoneon can be played very expressively, using various bellows pressures and other techniques.
Bandoneon
Early bandoneon, c. 1905
Alfred Arnold bandoneon, c. 1949
Ástor Piazzolla in 1971.