A phylum containing some 1200 species of free-living worms found chiefly in marine habitats but also in freshwater and soil. They have flattened bodies, sometimes patterned in striking colours, ranging from less than 1 mm to over 20 m long (hence their popular name of ribbon worms). Unlike flatworms, nemerteans have a complete digestive tract, with mouth and anus, and a blood vascular system. They also typically possess a long hollow muscular proboscis, which lies inverted inside a fluid-filled chamber, the rhynchocoel. The proboscis can be rapidly everted through its own pore and is used to catch prey, such as crustaceans, worms, and molluscs. It can also be used to assist burrowing in sediment or mud. Nemerteans may also crawl or swim by means of muscular undulations of the body. Reproduction can be sexual, with eggs developing directly into adults or via ciliated larvae. Asexual reproduction by fragmentation also occurs. Nemerteans are included in the clade Lophotrochozoa.