| Taxonomic name | Type | Description | Size (length) |
| Acanthocephala | phylum | parasitic worm | 65|cm|in}} |
| Annelida | phylum | segmented worms | 3|m|ft}} |
| Aplacophora | Sub-phylum | molluscs that look like worms | a few millimeters to several centemeters |
| Chaetognatha | phylum | arrow worms | 2|to|120|mm|in}} |
| Cycliophora | phylum | found living attached to the bodies of lobsters | less than ½ mm wide |
| Entoprocta | phylum | sessile aquatic worms | 0.1|to|7|mm|in}} |
| Gastrotricha | phylum | pseudocoelomate worms | 0.06|to|3|mm|in}} |
| Gnathostomulida | phylum | jaw worms | 0.5|to|1|mm}} |
| Hemichordata | phylum | deuterostome worms |
| Kinorhyncha | phylum | pseudocoelomate invertebrates, widespread in mud or sand at all depths | 1 mm or less |
| Loricifera | phylum | sediment-dwelling worms | 100 µm to ca. 1 mm |
| Micrognathozoa | superphylum | discovered living in homothermic springs | 0.1|mm|in}} |
| Nematoda | phylum | round worms | 5|cm|in}}, and some parasitic ones reaching over {{convert|1|m|ft}} |
| Nematomorpha | phylum | parasitic worms | 50|to|100|cm|in}} |
| Nemertea | phylum | invertebrate ribbon worms | 20|cm|in}} long, one specimen has been estimated at {{convert|54|m|ft}} |
| Phoronida | phylum | horseshoe worms | 2|cm|in}}, the largest are {{convert|50|cm|in}} |
| Platyhelminthea | phylum | flatworms |
| Priapulida | phylum | penus worms, general shape may recall the shape of a penis | 0.2|to|39|cm|in}} |
| Sipuncula | phylum | peanut worms | 2|to|720|mm|in}} |
| Teredinidae | Family | shipworms, which are marine bivalve molluscs | several inches to five feet. |
| Xenoturbellida | subphylum | bilaterian worm-like species | 4|cm|in}} |