The murkworm is a descendant of the beastworm. It has returned to the sea to eat bottom-feeding plents. Because it has adapted to breathe air, it has to surface in order to breathe. As a result, the microlungs on the top half of the creature are more developed than the bottom ones, which almost never see air. Its internal vibration sensing organ has adapted well to being able to hear underwater, though it is still very crude. The olfactory organs have been separated from the mouth, and they can smell scents in the water to a limited degree of success. The tip of their tail has flattened out into a fin, similar to an Earth whale's. The old shells are now as soft as the skin.
Artwork by OviraptorFan