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Polychaete Worms: Animals With Straight or Branched Bodies

Linda Crampton is a writer and experienced science teacher with an honors degree in biology. She enjoys writing about science and nature.

Ramisyllis multicaudata as depicted by an Australian Academy of Science artist

Ramisyllis multicaudata as depicted by an Australian Academy of Science artist

Weird and Fascinating Worms

When most of us hear or read the word “worm,” we think of a long and slender animal that crawls over a surface. This impression is often true. In the case of a strange polychaete known as Ramisyllis multicaudata, it isn’t. This highly branched animal was discovered inside a sponge in Australia. Scientists don’t know exactly how the worm survives or whether it harms its host, helps it, or has no major effect on its life. It’s a mysterious and fascinating animal.

Like earthworms, polychaetes (or polychaete worms) belong to the phylum Annelida. As in earthworms, their bodies are elongated and are segmented externally and internally. The animals have some distinctive features, which causes them to be classified in the class Polychaeta within the phylum Annelida. Earthworms are classified in the class Clitellata. Even when they don’t have a branched body, many polychaete worms are intriguing and even attractive animals. The group exhibits a wider variety of body features than the earthworm one.

Phyllodoce rosea lives in muddy ocean sediments in Europe. It’s known for its red pigment, which slowly disappears in preserved animals. Though many polychaetes have a body resembling that of Phyllodoce rosea, the group contains animals with a wonderful variety of body forms.

An illustration based on the anatomy of a polychaete named Nephtys hombergii

An illustration based on the anatomy of a polychaete named Nephtys hombergii

Polychaete Facts

Polychaetes are also known as bristle worms (or bristleworms). Unlike the case in earthworms, their segments bear a flap called a parapodium on each side of their body. Each parapodium bears bristles, which give the worms their common name.

A parapodium often has two lobes, as shown in the illustration below. The upper or dorsal lobe is known as the notopod and the lower or ventral one as a neuropod. There is a bundle of bristles on each lobe. The bristles are made of chitin and are technically known as chaetae. The term “polychaete” means “many bristles” and is derived from Latin and Greek words. Chitin is a polysaccharide. It forms the firm outer covering of insects and crustaceans and the scales of fish.

Unlike earthworms, polychaetes have a distinct head region. The head often bears eyes, through in general these are only capable of distinguishing light areas from dark ones. A group known as alciopid polychaetes have a more complex eye that contains a lens, however. Polychaete worms have a brain and a nervous system.

Polychaetes exhibit both sexual and asexual reproduction. The animals lack a clitellum, which is the thick ring around an earthworm’s body that plays a role in reproduction. Fertilization in polychaetes is generally external. The female releases eggs, and the male releases sperm. A larva known as a trophophore develops from a fertilized egg. The larva undergoes metamorphosis to become an adult. In the interesting world of polychaetes, some species reproduce in a different way.

July 1st is International Polychaete Day. It’s a day to celebrate the existence and features of bristle worms. The first celebration was held in 2015. Some of the impressive animals in the group are shown in the video above.

Interesting Types of Polychaetes

Most polychaetes are marine organisms. They are common animals in the ocean. A few species live in fresh water, and some live on land. Many interesting representatives of the group exist. I describe four of them below. Photos of the animals are shown in the sequence above.

Christmas Tree Worms

A group of colourful Christmas tree worms (Spirobranchus giganteus) may look artificial, but the animals are real. They live in a burrow that they create in a coral reef. They build a tube in the burrow for additional protection. The tube is made from body secretions. In order to trap tiny food items and obtain oxygen, the animals expand feathery appendages into the water. The appendages have a variety of colours and remind some people of a fir tree.

The worms are only around one-and-a-half inches in length, but the appendages are noticeable and add to the festive appearance of a group. I’ve been unable to discover why worms in a similar environment have appendages of a different colour. It’s an interesting question.


Multiple species of Tomopteris exist. They are small animals that range from half an inch to just over one-and-a-half inches in length. They are part of the plankton, or the community of tiny creatures that spend their lives drifting in ocean currents. They do have the ability to swim, however.

At least some species in the genus are bioluminescent animals. Scientists have discovered that some species release yellow luminescent particles from their body. Yellow bioluminescence is very unusual. The particles are shown in the video above.

Giant Tube Worms

Riftia pachyptila is known as the giant tube worm (or tubeworm). It lives on the sea floor in the Pacific Ocean. It’s found in areas where hydrothermal vents are releasing hot and mineral-rich water that contains sulphur.

The animal doesn’t catch its own food. The food that it obtains is made by bacteria that live in its intestine. The animals obtain oxygen through their gills. The gills are retracted when a predator approaches.

If water stops flowing out of a vent, the tube worm colony dies. The animals produce mobile larvae that find new areas with suitable vents. It’s unknown how the larvae find a suitable habitat.

Sand Worms or King Ragworms

The king ragworm can be a large and attractive animal. Its scientific name is Alitta virens. It’s also referred to as Nereis virens, which was its former scientific name. The worm sometimes reaches a length of four feet. Multiple colours can often be seen on its body, including blue, green, orange, pink, brown, and grey. It sometimes appears to be an iridescent animal.

The worm lives in a burrow that it creates in the sediments on the ocean floor. Its head emerges from the burrow to capture passing prey. It eats smaller animals, including crustaceans and other worms.

The ragworm sometimes leaves its burrow to find food. This exposes it to an attack by predators. Humans could be considered one of them. The animals are used as bait in the fishing industry.

The Body of a Sponge

Two species of branched polychaetes have been discovered. Both of them live in sponges, which despite their appearance are animals. As in other animals, the cells of a sponge are covered by a membrane but lack a cell wall. A sponge must obtain food from its environment instead of making it in its body as plants do.

Sponges have multiple pores called ostia on their surface. They also have a larger opening called an osculum. Water containing oxygen and tiny food items enters the animal through the ostia. The oxygen and food are extracted inside the sponge. Carbon dioxide waste and water are released through the osculum. Some sponges have multiple oscula.

Included are the yellow tube sponge, Aplysina fistularis, the purple vase sponge, Niphates digitalis, the red encrusting sponge, Spiratrella coccinea, and the gray rope sponge, Callyspongia sp.

— NOAA (with reference to the photo above)

Reproductive Features of the Family Syllidae

Ramisyllis multicaudata belongs to the family Syllidae. Other members of the family are known. With the exception of R. multicaudata and another species mentioned below, they aren’t branched. Some researchers suspect that more branched species exist, however. They may be difficult to find because they are hiding inside another organism.

Many syllids reproduce like other polychaetes by releasing eggs and sperm into the environment. Some use a different strategy. They produce a short and modified extension at the end of their body or less often short branches on the side of their body. The extensions and branches are called stolons and are temporary structures. The stolons are loaded with eggs or sperm. When they are mature, they break away from the adult’s body and travel through the water. Stolons containing eggs and sperm meet, and fertilization occurs. The missing end of the syllid is regenerated.

The process described above is interesting because a stolon is not just a sac of eggs or sperm. It has a head region, one or more eyespots, appendages, and chetae. It also contains muscle fibres and other items normally found in or on the worm. It‘s able to swim. The stolon doesn’t survive for long. Its sole function seems to be to find a stolon of the opposite gender and help the eggs and sperm to meet.

The family Syllidae is known for the presence of a muscular structure called the proventriculus that surrounds the digestive tract. It’s shown in the photo above. The proventriculus plays a role in enabling materials to travel along the digestive tract, but it may have additional functions.

Ramisyllis multicaudata

Christopher Glasby is a biologist who specializes in worms. He discovered Ramisyllis multicaudata in 2006 at a site called Darwin Harbour in Australia. The worm was located in a sponge belonging to the Petrosia genus. The members of this genus have many branching channels in their body. When they are mature, they have multiple oscula.

The biologist discovered that a Petrosia specimen that he had found had a filamentous structure sticking out of each osculum. When he dissected the sponge, he found the head of a polychaete worm inside it and a branch of its body inside each channel in the sponge. The tail of a branch was what he had seen projecting out of each osculum.

Scientists believe that the branches of the animal’s body develop by a modification of the stolonization process. The stolons of R. multicaudata are greatly elongated compared to those in most species, and they are branched. They also seem to stay attached to the worm for a long time. Researchers say that their tips are eventually released when they reach an osculum and that eggs and sperm of the species are then able to join. Recent research from University of Göttingen has discovered that the detached stolons of the species contain a brain and nerves.

It’s unknown how the worm obtains food while it‘s in a sponge. It may absorb nutrients that flow through the water that enters the animal, or it may obtain them from the tissues of the sponge. Many aspects of the worm’s life need to be discovered.

One other species of branched polychaete is known. From 1872 to 1876, a British naval vessel named HMS Challenger enabled scientists to explore life in the deep ocean. One of their discoveries was a sponge containing a Polychaete worm named Syllis ramosa.

The Discovery of New Life Forms

It isn’t surprising that we are still discovering new microorganisms. The tiny creatures are hard to observe without suitable magnifying equipment. We are still discovering new species of macroscopic animals, however. The abundance of life forms on Earth and their varying characteristics are awesome.

Ramisyllus multicaudata and Syllis ramosa are not microscopic, but they spend their lives hidden in the tissues of specific species of sponges. They can be hard to study because their body branches and extends through different parts of their host’s body, but the discoveries that are being made are fascinating. Polychaetes are a very interesting group of animals and may have more surprises to share with us.


  • Introduction to the class Polychaeta from the University of California Museum of Paleontology (UCMP)
  • Information about marine bristle worms from the Smithsonian Institution
  • Facts about Christmas tree worms from NOAA
  • Tomopteris facts from MBARI (Monterey Bay Aquarium Research Institute)
  • Giant tube worm information from MBARI
  • Meet the enormous king ragworm from Scientific American
  • The world’s weirdest worm from Taxonomy Australia, Australian Academy of Science
  • The worm that looks like a tree from New Scientist
  • Discovery of a branching sea worm in a sponge from the ScienceDaily news service

© 2021 Linda Crampton


Linda Crampton (author) from British Columbia, Canada on May 06, 2021:

Thank you for the visit and comment, EK. Blessings to you as well.

EK Jadoon from Abbottabad Pakistan on May 06, 2021:

That was an interesting read, Alicia. I think, Tomopteris are bioluminescent and can glow . All the photos are eye-catching.

Thanks for sharing the information.


Linda Crampton (author) from British Columbia, Canada on May 06, 2021:

I appreciate your comment, Devika. Polychaetes are interesting to explore.

Devika Primić from Dubrovnik, Croatia on May 06, 2021:

AliciaC This is such an interesting about the different worms. I had no idea of. these types of worms. Informative and fascinating.

Linda Crampton (author) from British Columbia, Canada on May 06, 2021:

I’m glad the article was helpful! I understand why some people don’t like earthworms, but I enjoy observing them.

Mary Norton from Ontario, Canada on May 06, 2021:

Linda, I don't like worms. It took me longer to appreciate earthworms and not be afraid of them, but knowing more about these worms from your article makes me look at them more favourably.

Linda Crampton (author) from British Columbia, Canada on May 05, 2021:

Thank you very much, Fran.

Linda Crampton (author) from British Columbia, Canada on May 05, 2021:

Hi, Adrienne. Yes, the discoveries made by biologists are very interesting. Thank you for the comment.

Adrienne Farricelli on May 05, 2021:

Your article on polychaetes worms has surely been an eye opener as I never heard about them before. It's very intriguing to learn that we are still discovering new microorganisms.

fran rooks from Toledo, Ohio on May 05, 2021:

Alicia, you never cease to amaze me with your informative articles. Thanks for sharing.

Linda Crampton (author) from British Columbia, Canada on May 05, 2021:

Thanks, Bill. Worms can be very interesting organisms.

Linda Crampton (author) from British Columbia, Canada on May 05, 2021:

Thank you, gyanendra. I appreciate your kindness.

Bill De Giulio from Massachusetts on May 05, 2021:

Another very informative article on something I knew very little about. Who knew that worms could be so interesting. When I think of worms I think of the slimy, brown worms found in the soil. I had no idea they could be so colorful. Great job, Linda.

gyanendra mocktan from Kathmandu,Nepal on May 05, 2021:

AliciaC, thank you very much for taking me to the fascinating world of worms. It was a pleasure learn from you.

Thank you.

Linda Crampton (author) from British Columbia, Canada on May 04, 2021:

Thank you for such a kind comment, Chitrangada. I always appreciate your visits.

Chitrangada Sharan from New Delhi, India on May 04, 2021:

Normally any creature like these, would be called worms by most of us. I didn’t know any details about them. Nature is full of such amazing creatures and as a common person, we hardly have any knowledge about them.

But, your educational articles always enlighten us with interesting information. This is a well written and well researched article about Polychaetes and worms with branched bodies.

As I always say and believe that you are an asset to HubPages.

Thank you for sharing another wonderful article.

Linda Crampton (author) from British Columbia, Canada on May 04, 2021:

Hi, Ravi. Thanks for the visit. There are a few species that may hurt humans. As is true for most wild animals, it’s best to admire them without touching them if we don’t know what species they are or whether they’re harmless.

Ravi Rajan from Mumbai on May 04, 2021:

Thanks for this very informative article on polychaete worms.I had no idea that they exist in so many forms from sand to tube worms. Thanks for sharing.

One question - are there any poisonous varieties in these worms that might harm humans ?

Linda Crampton (author) from British Columbia, Canada on May 04, 2021:

Thank you for the visit and the kind comment, Misbah. Blessings to you as well.

Linda Crampton (author) from British Columbia, Canada on May 04, 2021:

Hi, Dora. Yes, polychaetes and many other animals are marvelous creatures. Thank you for commenting.

Linda Crampton (author) from British Columbia, Canada on May 04, 2021:

Hi, Flourish. Yes, life on a Earth is certainly as fascinating as space exploration. There’s almost certainly a lot more to learn about polychaete reproduction. I appreciate your visit.

Dora Weithers from The Caribbean on May 04, 2021:

Amazing facts is a good term for all this information about the worm. Generally, I would want to avoid it, but you make me want to examine it. Thanks for these educational articles on these marvelous creatures.

FlourishAnyway from USA on May 04, 2021:

Your description of the stolons and reproduction made me think that it's such a lottery that it would find what it needed. This was an amazing presentation of nature that we barely know much about. With all the excitement and attention to space exploration, you'd think we would at least understand what's on our own planet a little better first.

Misbah Sheikh from — This Existence Is Only an Illusion on May 04, 2021:

This is a very well-researched and well-structured article, Linda. I never knew that much about different kinds of worms before. Very intriguing studies. Thanks for sharing this informative and interesting hub.

Blessings always

Linda Crampton (author) from British Columbia, Canada on May 04, 2021:

I appreciate your visit and comment very much, Pamela.

Linda Crampton (author) from British Columbia, Canada on May 04, 2021:

Thank you for the kind comment, Peggy. I think nature is fascinating. I agree with your opinion about Christmas worms!

Pamela Oglesby from Sunny Florida on May 04, 2021:

The Christmas tree worms and the Tomopteris worms, plus many others were new were totally new to me, Linda. This is an interesting article with a wealth of new information. Thank you for sharing it, Linda. I think I will read over this article again.

Peggy Woods from Houston, Texas on May 04, 2021:

Wow! I learn something new with most of your well-researched articles, and this one is no exception. It is amazing at all of the life forms that we are still discovering! Those Christmas tree worms are gorgeous!