Systematics and Taxonomy
Nerertines have traditionally been considered acoelomates, and as the sister taxon to the acoelomate flatworms, and have solid bodies (Brusca and Brusca 2003). However, new morphological and molecular analyses now suggest that their body cavities, the rhynchoceol and circulatory system, may in fact be homologous to the coelomic cavities of animals within the Lophotrochozoa Halanych 2004, Tuberville et al 1992). The relationships within the phylum have also been investigated with molecular markers, and in most cases support traditional classifications (Thollesson and Norenburg 2003). There is no fossil record for the Nemerteans. This is not suprising since they have soft bodies, but even their mineralized stylets have not been found (Waggoner and Collins 2001).