Spirorbis corallinae is a very small (1-2 mm) coiled polychaete that lives attached to seaweed in shallow saltwater. It has a smooth, white or semi-translucent, sinistral (left-handed) coiled shell encasing an orange body about 1.5 mm in length. It lives primarily on the red algae Corallina officinalis, after which it takes its name, but is also known to live on Irish Moss (Chondrus crispus). The shell is often confused with the white growing tips of Corallina fronds.