Phylum Gnathostomulida:

                This phylum contains about 80 species of tiny marine worms. These worms are unique due to the
        presence of a pair of hard jaws. They live mainly along the coastal shorelines and use their hard jaws to
        scrape fungi and bacteria from the particles.
                Gnathostomulids have no coelem or pseudocoelem (refer to bilaterally symmetrical animals page),
        and there is only one opening from their digestive cavity.

          Phylum Rhynchocoela:

                Phylum Rhynchocoela includes about 650 species of acoelomate worms, commonly called ribbon
        worms or nemertines. They are characterized by a proboscis; a long, retractile, slime-covered hollow
        tube, which may be armed with a barb. They use the proboscis to capture prey. Some inject a paralyzing
        poison into their prey.
                Unlike the digestive cavity of cnidarians and flatworms, ribbon worms have a one-way digestive
        track beginning with a mouth and ending with an anus. The two-opening tract is much more efficient  than
        the one opening arrangment because eating can be continuous and various segments of the tract can
        become specialized for different stages of digestion.
                For reproduction in ribbon worms, fertilization occurs externally. Also, asexual reproduction may
        result by fragmentation of the body and regeneration of whole worms from the parts.
 
 

       Thanks to the sites: http://phylogeny.arizona.edu/tree/eukaryotes/animals/nemertea/nemertea.html and
       http://rainbow.ldeo.columbia.edu/ees/life/slides/oldec/gnathostomulida.html for the pictures.