Ribbon Worms or Nemerteans

Ribbon Worms

Ribbon worms are rarely, but occasionally, found in marine reef aquaria.  They probably enter as hitchhikers on live rock.  These are often long worms, the largest are well over 100 feet (30 m) long, and they lack segments or any side appendages, characteristics that will distinguish them from the "bristle worms" or polychaete annelids.  Different species are colored differently and they are often brilliantly colored.   They catch their prey with a long extensible proboscis that is often tipped with a venomous barb.  They may eat crustaceans or various other worms.   They move by a combination of gliding and "peristalsis" (or the passing of waves of muscle contractions and elongations down the body).  Unlike the flatworms that they superficially resemble, they have a complete gut with mouth and anus, and a circulatory system. 

 

Photographs, courtesy of Guy Comstock, of a nemertean found in his aquarium.  The shots of the body show some of the changes in shape that occur, and the close-ups of the head, from the bottom showing the mouth, and from the top showing the sensory cephalic slits are useful for identifying other ribbon worms.  Compare these photos to a those of a bristle worm and note the lack of segmentation or lateral appendages.