What is the high pitched round backed guitar in Mariachi?

The high-pitched round-backed guitar in Mariachi is called a vihuela. It is a member of the lute family and is closely related to the guitarra de golpe, a small guitar used in traditional Spanish music. The vihuela is typically played with a pick, and its strings are tuned in a high register, giving it a bright, piercing sound. It is often used to play melodies or to provide rhythmic accompaniment in Mariachi music.