The paddle wheel of a pedalo is a smaller version of that used by a paddle steamer. A two-seat pedalo has two sets of pedals, side by side, designed to be used together. Some models, however, have three pedals on each side to allow a person boating alone to pedal from a centrally seated position.
The earliest record of a pedalo is perhaps Leonardo da Vinci's diagram of a craft driven by two pedals.
Media related to Pedaloes at Wikimedia Commons