Muscle

The light band of myofibril contains the protein actin, which is responsible for muscle contraction. The other proteins like myosin, troponin, and tropomyosin are involved in muscle contraction but are not part of the light band. Myosin is part of the dark band (A band) in the myofibril.

Cephalochordates, such as Amphioxus, have segmented muscle blocks called myotomes which are essential for movement and locomotion.