Sea worm may refer to one or several of the following taxa:
| Taxonomic name | Type | Description | Size (length) | |
| Acanthocephala | phylum | parasitic worm | ranges from a few millimeters up to 65cm (26inches) | |
| Annelida | phylum | segmented worms | ranges from microscopic to 3m (10feet) | |
| Aplacophora | Sub-phylum | molluscs that look like worms | a few millimeters to several centimeters | |
| Chaetognatha | phylum | arrow worms | 2mm120mm | |
| Cycliophora | phylum | found living attached to the bodies of lobsters | less than ½ mm wide | |
| Entoprocta | phylum | sessile aquatic worms | ranges from 0.1mm7mm | |
| Gastrotricha | phylum | pseudocoelomate worms | 0.06mm3mm | |
| Gnathostomulida | phylum | jaw worms | 0.5to | |
| Hemichordata | phylum | deuterostome worms | a few centimeters to 2,5 meters | |
| 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 | 0.1mm | |
| Nematoda | phylum | round worms | ranges from microscopic to 5cm (02inches), and some parasitic ones reaching over 1m (03feet) | |
| Nematomorpha | phylum | parasitic worms | 50cmto100cmcm (20inchesto00inchescm) | |
| Nemertea | phylum | invertebrate ribbon worms | most are less than 20cm (10inches) long, one specimen has been estimated at 54m (177feet) | |
| Phoronida | phylum | horseshoe worms | 2cm (01inches), the largest are 50cm (20inches) | |
| Platyhelminthea | phylum | flatworms | ||
| Priapulida | phylum | penis worms, general shape may recall the shape of a penis | 0.2cmto39cmcm (00.1inchesto15inchescm) | |
| Sipuncula | class | peanut worms, a group of unsegmented marine annelids | 2mm720mm | |
| Teredinidae | family | shipworms, which are marine bivalve molluscs | several inches to five feet. | |
| Xenoturbellida | subphylum | bilaterian worm-like species | up to 4cm (02inches) |