The circulatory system has been lost, and the coelomic fluid has taken over the role of transporting oxygen, nutrients and gametes.

Instead of a heart the inner surface of the worm is covered with cilia that moves the fluid around inside the body.

A series of extretory organs called metanephridia consists of ciliated funnels which opens to the coleomic cavity and connects with the exterior though a nephridiopore.

[9][10] The animals use a type of propulsion called metachronal paddling, a sequential movement of multiple appendages.

It is also able to change the surface area of each parapodia by spreading and contracting its two fleshy ends, which creates differences in drag between power and recovery strokes.