Spirorbis spirorbis is a small (3-4 mm) coiled polychaete that lives attached to seaweeds and eel grass in shallow saltwater.They have a smooth, white, sinistral (left-handed) coiled shell encasing an orange body about 3 mm in length. The tube has a peripheral flange where it attaches to the substrate.The worm has a short abdominal region and a slightly broader thorax terminating in ten stiff tentacles, used to filter food from the water.