Diopatra cuprea are on average 12 inches long and 3/8 of an inch wide. They live in a leathery tube, which they make out of mucus, bits of shells and rocks. When they come out of their shells they look similar to Christmas trees; however they are not often seen. Their shells are spirals that are cylindrical at the front and flat and tapered at the end. The color of their tube is reddish to brown and speckled with gray. They have many appendages. The lobe above their mouth is oval and short with one pair of short conical antennae. They also have five long antennae with ringed bases on the top. They have large jaws and the segments between 4 or 5 and 35 have bushy gills on their upper surfaces. These bushy gills are the "plumes" that give the plumed worm its more common name. (Carson 1955; Klingel 1951; Knopf 1981)