The prokaryotes are classified into two domains, the bacteria and the archaea domains. This makes them unique as the other organisms fall into one of the three domains, not in two of them. The prokaryotes come in many different shapes. They all do fall into three categories, bacilli (which are the rod-shaped prokaryotes), spirilli (which are the spiral-shaped prokaryotes), and cocci (which are the spherical shaped prokaryotes).
