Ribbon worms, or nemerteans, are long, unsegmented worms that comprise their own phylum. All nemerteans have a retractable proboscis that they use to capture prey, which in some cases can have one or more venomous barbs. Most nemerteans are much longer than wide, and in some cases, an individual only a few millimetres wide can be several metres long. Ribbon worms are mostly carnivorous, feeding on annelids and molluscs.
