Ribbon worms belong to the phylum Nemertinea. They are worms with unsegmented bodies, measuring only a few inches long. They have long extensible proboscises for capturing food. The proboscis lies above the mouth and can be extended to a distance sometimes equal to the length of the worm body. They are all carnivorous and usually feed on annelid worms. They are commonly found on the ocean bottom living between tide marks under stones or seaweed or coiled up in burrows in muddy sand.
Ribbon worms show two significant evolutionary advances over the flatworm: a digestive system with two openings (a mouth and an anus) and a circulatory system for transporting substances from one part of the body to another.