There are three main instrument families in Gamelan that fulfil different functions: the balungan instruments play the nuclear theme, which is called the balungan, interpunctuating instruments divide the phrases and mark new sections, and the panerusan instruments play embellished variations of the theme. The balungan instrument is commonly a metallophone or more specifically the saron which is a single octave instrument of seven metal bars. Important interpunctuating instruments are the gong ageng (a large gong), the kempel (a collection of medium sized gongs), and the kenong (a smaller, horizontal kettle-like gong). Panerusan instruments include the gambang (a wooden, xylophone-like instrument), the bonang (collection of small, horizontal gongs), and the celempung (a plucked zither-like instrument).