Names used for nemertean genera and species of the world are listed alpha-betically, with their original description citations, synonymy and current taxonomic status. Though many remain inadequately described, 250 genera and 1149 species are recognized as valid; these comprise Archinemertea (3 genera, 28 species), Palaeonemertea (11, 70), Heteronemertea (79, 401), monostiliferous Hoplonemertea (91, 500), reptantic polystiliferous Hoplonemertea (22, 45), pelagic polystiliferous Hoplonemertea (40, 97), Bdellonemertea (1, 5) and three monotypic genera whose higher taxonomic affinities are uncertain. In addition, three monotypic genera of fossil Nemertea are also listed. The higher systematic position and typical ecological habits of its species are shown for each valid genus, type-species are indicated, and brief details of species known habitats and distribution are noted.