The shamisen or samisen (味線, literally three strings), also called sangen (絃), is a three-stringed, Japanese musical instrument played with a plectrum called a bachi. The yokin in a kind of prototype koto (箏), a traditional Japanese stringed musical instrument, similar to the Chinese zheng, the Mongolian yatga, the Korean gayageum and the Vietnamese đàn tranh. The koto is the national instrument of Japan. The kokin (古琴) is a Chinese seven-stringed zither called a guqin in Chinese. Sankyoku is a form of Japanese chamber music played on the koto, shamisen, and shakuhachi, often with a vocal accompaniment.