Behind the mouth the body becomes dorso-ventrally flattened and often has wrinkles and folds which gives the worm its convoluted appearance.

The colour of this worm is somewhat variable; it is usually greyish-brown with pale or transparent edges, but the dorsal surface in older individuals is often darker than the ventral surface; other individuals are slate blue, dark brown or greyish-green.

The pinkish nerve cords are often visible through the pale edges of the worm, and in young individuals the cerebral ganglia and the folded proboscis may also be discernible through the skin.

[2] Cerebratulus marginatus is native to the northern hemisphere, occurring in the Arctic and the North Atlantic Ocean, as far south as the Mediterranean Sea in the east and Cape Cod in the west.

The proboscis is able to be turned inside out to grasp prey and the diet consists of such invertebrates as clams and polychaete worms.