(Phylum Annelida)
Serpula columbiana, Platyhelminthes, Nemertea, Annelida, Chaetognatha, Hemichordata, Polychaete, and Phoronida are all kinds of marine worms. Some are harmless, some are beautiful, and some can sting with powerful toxins.
Calcareous Tubeworm
The calcareous tubeworm is a filter feeder that feeds on tiny microscopic organisms and small particles. When feeding, the animal extends the feather duster tentacles from its tube. Links of cilia on these tentacles force food particles toward the mouth. Read More….
Clam Worm
This clamworm is an important source of food for bottom-feeding fish and crustaceans. Birds will feed on them after spawning and die. Other common names for the clam worm are ragworm, mussel worm, pile worm, and sandworm. Read More….
Northern Feather Duster Worm
Northern feather duster worms live in tough brownish-to-white tubes that can grow to about 25 cm long. They have retractable feathery appendages at the end of the tube that capture food and act as gills for gas exchange. Read More….
Phylum Platyhelminthes includes flatworms. These are among the simplest of animals, consisting of essentially a flattened tube of muscle and a simple digestive system with a single opening that serves as both mouth and anus. It has no true body cavity, nor does it have the distinct body segments that characterize more complex worms. The vast majority of species in this phylum are parasites.
The ribbon worms in the phylum Nemertea are slightly more complex. While they also have a flattened shape, they have a one-way digestive system with a separate mouth and anus and a simple blood vascular system. Nemertea are carnivores that hunt in the sediments for prey.
The annelids include polychaete worms and leeches. These are the segmented worms. Also included are the tube and fan worms, or feather duster worms.
Phylum Chaetognatha is a relatively unknown group of worms. They typically locate their prey by detecting vibrations produced by copepods and other zooplankton. They use sharp hooks and teeth at the front of the body to grab their victims and immobilize them with neurotoxins.
The hemichordates are the closest relatives of the chordates and other invertebrates. Thus, these marine worms are described as the sister group of such animals as sea urchins.
The Phoronida, also called the horseshoe worms, are an exclusively marine group of lophophorate animals. The Phoronida is one of the smallest and least familiar of the marine worms; there are about twelve or so living species.

You have greatly understated the size of Clam Worms I used to earn my spending money digging and selling them ON Canvey Island and had the reputation of Providing the best quality and Giant specimens I never took worms under 25 Cm in length as they were unsaleable and considered as too small for a bait.
Typical Length is 35 to 55CMS in length 5 to 9 cm in diameter at the head. 12 inch (30 Cms smallest saleable ) are most common 75 to 125 Cms 48 inches and big enough to get its pincers around my boyish wrist . These would command as much as 2 dozen 30 cm ones My record was 56.5 inches relaxed. I am certain larger ones will or have been found.
I stumbled on a spot that only emptied in the march spring tides And that area can be located as behind a Man made tidal pool used as a low tide swimming pool. Located East of the Beach Hut Just south of the Line from the end of MEADWAY a short street just behind the soccer pitch. The beach at Canvey is Compromised of ground Cockle Shells Baby Clams The putrid odour of rotting clams is a tell tale sign of SUPPER RAGWORMS at work. MARCH tides are highest all year and thus the lowest the only time the pool empties enough to harvest thus the worms feed undisturbed for many years. I do not recall ever seeing others work the pool shell bed. But I last lived in the uk in 1963. I trust this correction helps you correct your mentioned data . Yes I have lost some flesh to these prehistoric beings. if they can crush a clamshell a finger is easy to rip. especially with some of the monsters I have captured. I Caught a 45 pound Cod on a portion of my record.
Peter
Hi Peter, the clam worms that we find here on Vancouver Island are the alitta succinea and rarely reach over 15cm in length, the giant ragworms that you are referring to are the alitta virens that can reach a whopping size of 90cm. The ones in the photos around 10cm and were photographed by me in Menzies bay just after a spawn.