A bright red worm, with an acorn shaped proboscis and a fleshy "collar". The body is segmented.

Found amongst seaweed such as bladder kelp holdfasts or coralline algae. Often found in groups.

Generally a surface deposit feeder, feeding on organic material on the substrate surface. They can, however, filter small particles out of the water using mucous and sticky cilia.

Can give off an odd antiseptic smell, which is thought to deter predators. They have features of chordates (animals with a dorsal nerve cord) such as a nerve net and gills, but new research has shown that these strange animals are more related to echinoderms than to true chordates.