How do lancelets move through water?

Lancelets, also known as cephalochordates, move through water by using undulations of their bodies. This locomotion is achieved by contracting muscle blocks known as myotomes, which run along each side of the body.12

Because these muscle blocks are staggered on either side, their contraction produces a side-to-side movement that allows the animal to swim both forward and backward. Additionally, lancelets use rapid body movements to burrow into sand or gravel, where they spend much of their time. They are not buoyant and will sink quickly if they stop their swimming motions.23