Split from the Mudworm, the Wriggler continues to shrink its rigid cuticle. This, however, does not leave it defenseless, since its speed and nimbleness make up for its lack of armour. Exposure of the non-armoured skin to water led to evolution of actual, retractable gills on the "cephalic" segment. With the development of primitive, bristly parapodia from the simple nubs possessed by its ancestor, it is now capable of "swimming" in the sediment as well as in the water column. It also has some sort of pseudo-statocyst to aid in catching balance while escaping predators.
The Wriggler reproduces similar to its ancestors, with eggs being laid into sand. However, their lifecycle now includes a free-swimming larva which feeds by trapping anything smaller than itself on a mucous mesh secreted from underside of the head. The mesh and its content is then withdrawn and digested.