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Acorn Worm Facts and the Regeneration of Human Body Parts

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

Impressive and Potentially Helpful Animals

Acorn worms are marine animals that have an impressive ability to replace lost body parts. Surprisingly, humans have many of the same genes as the animals, including most—and perhaps all—of the ones involved in regeneration. For an unknown reason, the regeneration pathway isn't active in us. If we could find a way to stimulate the correct genes, it might be possible for humans to regrow lost body parts. Scientists are studying worm and human genes with this goal in mind.

Acorn worms belong to a group known as hemichordates. This group is related to another group of organisms known as chordates. Humans and other vertebrates are chordates. Acorn worms are not closely related to earthworms, which are invertebrates, even though the abbreviated term "worms" is sometimes used to refer to the animals.

An Acorn Worm Digs in the Sand

The prefix hemi means half. Hemichordates could be thought of as half way between invertebrates and chordates. Acorn worms belong to the class Enteropneusta within the phylum Hemichordata. Many species of acorn worms exist, though the stated number varies widely.

Body Features of an Acorn Worm

Biologists divide the acorn worm's body into three sections—the proboscis, collar, and trunk. The proboscis is at the front of the worm. It's elongated and often conical in shape. The collar is a fleshy, ring-like structure behind the proboscis. The trunk is the longest section of the animal. The worms range from less than an inch in length to as long as seven feet.

Acorn worms are named from the fact that the proboscis and collar sometimes resemble an acorn (the fruit of an oak tree) sitting in its cup. Some people think that the region looks more like a structure found in a male human than an oak tree, however.

Most acorn worms have a dull yellow, pale orange, or pale pink colour. Researchers exploring a deep sea environment recently discovered beautiful purple worms. The animals are shown in the videos below. They have a slightly different appearance as well as a different colour from the worms found at shallower depths.

The front end of acorn worms reminds some people of the fruits of an oak tree.

The front end of acorn worms reminds some people of the fruits of an oak tree.

The Proboscis and Collar

The proboscis is a muscular structure that enables an acorn worm to dig its way through the sand or mud. The worm has no eyes, ears, or other structures that we might expect on the head of an animal. The skin of the entire animal contains sensory receptors, however. These probably enable it to sense light, chemicals, and touch. The skin cells are ciliated. Cilia are tiny hair-like structures that beat to create a current of liquid.

Chordates have a flexible, rod-like structure called a notochord in at least some stage of their lives. In humans, the notochord is replaced by the spinal column during embryonic development. Acorn worms have a similar structure to a notochord called a stomochord, which develops no further. Most of the stomochord is located under the collar.

The mouth is located on the underside of the worm between the proboscis and the collar. The worm has a complete digestive tract that travels from the mouth, through the trunk, and to the anus at the end of the trunk. The mouth leads to the pharynx, which is in turn followed by the esophagus, stomach, and intestine.

Structure of the anterior (front) end of an acorn worm

Structure of the anterior (front) end of an acorn worm

The Trunk of the Animal

The trunk contains many of the worm's organs. Some of the structures described below extend from the trunk into the collar and even into the proboscis, however.

Respiratory System

The gill slits are located behind the collar. Water enters the worm via the mouth and then flows over the gills. Oxygen leaves the water and enters the blood vessels of the gills while carbon dioxide moves from the blood into the gills. The water leaves the body and returns to the sea through the gill slits.

Circulatory System

A vessel along the animal's back (the dorsal vessel) sends blood to the proboscis. Here a muscular sac acts as a heart. Blood travels backwards through a vessel on the lower surface of the worm (the ventral vessel). The worm has an open circulatory system, which means that the blood is not confined in blood vessels throughout its route. In some places, it travels through spaces called sinuses. The blood is colourless and contains dissolved substances but no cells.

Nervous System

The nervous system appears to be quite simple but requires more study by scientists. The animal has a dorsal nerve cord along the upper part of its body and a ventral one along the bottom part. The cords are connected via a ring-like structure around the pharynx. The animal also has a plexus (a collection of branched nerves) under its skin. It has no brain, however.

Excretory System

The excretory organ is located next to the heart and is known as the glomerulus or the kidney. This organ removes waste from the blood.

An Acorn Worm on the Deep Sea Floor

The acorn worm above was discovered by the NOAA (National Oceanic and Atmospheric Administration) Okeanos Explorer team. The animal was found during an expedition known as the 2016 Deepwater Exploration of the Marianas.

Life of an Acorn Worm

Acorn worms live in u-shaped tunnels that they create in the sand or mud of either intertidal areas or areas covered by deeper water. The animals are rarely seen by humans. One end of the tunnel is used for feeding and the other end for defecation. The skin contains glands that secrete mucus, which lines the tunnel. The worms tend in stay in one place once they have dug their burrow, although they are capable of slowly crawling from one spot to another. The proboscis is the most active part of the worm during digging and feeding, but the collar helps the digging process.

Most worms swallow sand or mud and extract detritus from it. Detritus consists of tiny fragments of dead and decomposed creatures as well as particles of their waste material. The sand is swept towards the worm's mouth by cilia on the proboscis and collar. Once the detritus is extracted, the sand is expelled through the anus at the surface of the burrow, produced worm-shaped castings reminiscent of those left by earthworms.

Some acorn worms can obtain nutrients by filter feeding. Sea water enters the body through the mouth and exists via the gills. Suspended particles in the water are trapped on the gills and retained for food.

Lifecycle of a specific acorn worm (Belanoglossus simodensis)

Lifecycle of a specific acorn worm (Belanoglossus simodensis)

Reproduction Facts

Acorn worms are either male or female. The female releases a mass of eggs covered with mucus. The male releases sperm. Once the sperm fertilizes the eggs in the sea, the mucus breaks down. The young worm develops while in the ocean. In some species of hemichordate, the youngster looks like a juvenile worm. In others, it looks quite different from the adult and is known as a tornaria larva, as shown in the illustration above. At least some species of acorn worms can reproduce asexually when bits of the worm's trunk break off and grow into new animals.

The larvae of acorn worms closely resemble those of the phylum Echinodermata, which contains starfish, sea urchins, and sea cucumbers. Certain structural features and aspects of embryonic development link echinoderms to chordates. These links between the phyla cause biologists to place echinoderms, hemichordates, and chordates in one group called the deuterostomes.

Regeneration Abilities

Researchers at the University of Washington (UW) have published the results of a detailed exploration of acorn worm regeneration. If a worm is cut in half between the head and the tail, each worm grows the missing half in the correct proportion. All of the lost internal organs and structures are replaced, and they are each in the correct position and of the correct size and shape. In fact, it's impossible to distinguish the regenerated worms from the original one. If each of the new worms is cut, the regeneration process is repeated.

The researchers found that by day 15 after a worm had been cut into two sections, the damaged pieces had regrown the missing organs, nerves, and body structures. Furthermore, all of these parts were functional.

Regeneration in Acorn Worms

We share thousands of genes with these animals, and we have many, if not all, of the same genes they are using to regenerate their body structures.

— Shawn Luttrell, University of Washington

Possible Application to Human Biology

The UW researchers studied gene expression in the acorn worms as they regenerated. Genes control the construction of a body and the action of body processes by coding for proteins. The phrase "gene expression" means that a gene becomes active. The researchers suspect that a master gene or genes controls the other genes involved in the regeneration of an injured acorn worm.

The scientists hope to find a similar genetic control mechanism in humans. If they do, it may be possible to take a tissue sample from an injured person, trigger the correct genes to become active and then place the sample over the injury as a graft. If all goes according to plan, the missing structure will be regenerated.

Current Regeneration Abilities in Humans

Humans currently have a very limited ability to regenerate structures in the body. Some examples of natural regeneration locations include:

  • skin
  • the endometrium in the uterus (lost during each menstruation and then regenerated)
  • fingertips (under some conditions)
  • the liver, provided at least a quarter of the organ is still present

Regenerating entire nerves after they are injured, replacing whole organs after devastating damage, and replacing amputated limbs would be wonderful advances in medical science. Acorn worms may show scientists how to accomplish this.

I really think we as humans have the potential to regenerate, but something isn’t allowing that to happen. I believe humans have these same genes, and if we can figure out how to turn on these genes, we can regenerate.

— Billie Swalla, Friday Harbor Laboratories Director

Regeneration via Stem Cells

The UW researchers are trying to discover whether acorn worms use stem cells to produce new body parts or whether other cells are reprogrammed. Stem cells are unspecialized but can be stimulated to form specialized cells under the right conditions. Interestingly, medical scientists have achieved some success in inducing the regeneration of human tissue and structures via stem cells. Perhaps stimulating stem cells and stimulating genes that we share with acorn worms will both be helpful for regeneration in the future.

Why Can't Humans Regenerate Lost Body Parts Naturally?

It's not known for certain why humans lack natural regeneration capabilities beyond a few cases. According to the University of Washington researchers, there are at least two theories that may explain the situation.

When a piece of the body is broken off, our immune system may react so strongly to prevent blood loss and infection that it produces scar tissue that prevents regeneration. Another factor involved may be that since we are so much larger than an acorn worm, the energy required to create a new body part may be too high.

Acorn Worm Genes and Humans

About seventy percent of human genes have a counterpart in acorn worms. It's strange to think that a creature that looks so different from a human being and that is relatively primitive in function could share so many genes with us. Understanding how the genes of the worm work may be very helpful for humans. Regeneration of our lost body parts could have a dramatic effect on our lives.


Questions & Answers

Question: How do members of the class Enteropneusta regenerate?

Answer: For a more detailed look at how the animals regenerate, you could go the University of Washington news release mentioned in the "References" section of my article and then click on the relevant link in the news release to explore the scientific paper. The research is interesting, but it includes too many details to summarize properly here.

© 2016 Linda Crampton


Linda Crampton (author) from British Columbia, Canada on May 22, 2020:

Hi, Peggy. Yes, it would be fantastic. Scientists might discover some very important and relevant facts while studying the animals.

Peggy Woods from Houston, Texas on May 22, 2020:

It would be fantastic if researchers could discover a way to activate a gene that would trigger the regeneration of lost body parts in humans, similar to what this acorn worm can do. Thanks for introducing me to another sea creature, of which I knew nothing.

Linda Crampton (author) from British Columbia, Canada on May 01, 2019:

Regeneration of lost body parts would be a wonderful ability. I hope it becomes possible one day.

JK ehsan on April 30, 2019:

that was amazing look so pretty i hope during evolution process we can regenerate our body lost part ..............

Linda Crampton (author) from British Columbia, Canada on December 23, 2017:

Thanks for sharing your memory, Jackie. I don't mind the worms that you describe. I know they aren't popular with some people, but I've always enjoyed watching them!

Jackie Lynnley from the beautiful south on December 23, 2017:

Came back for a visit but picked the wrong one! I always hared worms. In first grade walking to school I would see them drowned in mud puddles and it would be all I could do not to throw up before I got to school.

Am sure I shouldn't have told you this so close to suppertime...but you know me and memories...can't keep my mouth shut!

Linda Crampton (author) from British Columbia, Canada on October 17, 2017:

I think so, too, jacksonkirk!

jacksonkirk on October 17, 2017:

omg so cool

Linda Crampton (author) from British Columbia, Canada on September 29, 2017:

Hi, Kari. I agree—acorn worms and regeneration are very interesting. Thank you for the comment.

Kari Poulsen from Ohio on September 29, 2017:

Very interesting. It is amazing we share so many genes with the acorn worm. Regeneration is an amazing subject.

Linda Crampton (author) from British Columbia, Canada on July 13, 2017:

Thank you very much, Sara.

Sara Krentz from USA on July 13, 2017:

This was a fascinating read; I had never even heard of acorn worms.

Linda Crampton (author) from British Columbia, Canada on January 09, 2017:

Thank you very much for the kind comment, Demas.

Demas W. Jasper on January 09, 2017:

The Summary was very helpful here. The article can be universally of interest as all potential readers could benefit personally. You gave enough detail for those who work in related fields to get an idea of what current research is seeking to solve. Thanks.

Linda Crampton (author) from British Columbia, Canada on December 28, 2016:

Thank you, Dianna. It's very interesting to think about the possible applications of the research in human biology.

Dianna Mendez on December 28, 2016:

This was quite interesting and educational. You always give me something new to think about: what if this were possible for humans? As you say, we already to generate a few parts on our own.

Linda Crampton (author) from British Columbia, Canada on December 26, 2016:

Thank you very much for the visit and comment, Suhail. It would be great if researchers found a way to safely regenerate damaged body parts in humans. I hope this happens one day.

Suhail and my dog K2 on December 26, 2016:

Hi Linda,

First I couldn't get myself to start reading, but when I did, I found it to be a very easy read. It was very informative and you used layman's terms throughout to keep the readers' interest going.

Btw, thanks for sharing the research theories on why can't we be able to regenerate lost body parts. I never thought about it. Well, the consolation is that we have company in this regard of many other animals.

Linda Crampton (author) from British Columbia, Canada on December 20, 2016:

Thank you very much, Ann. I appreciate your kindness. I hope you have a merry Christmas and a happy near year.

Ann Carr from SW England on December 20, 2016:

What a fascinating creature! Thanks for the clear explanation. It's strange that our regeneration capabilities aren't as developed as theirs if we have a similar innate ability.

You have a great knack of explaining such intricate things in an entertaining way, Linda. I enjoyed reading and learnt much.

Hope you have a Happy Christmas!


Linda Crampton (author) from British Columbia, Canada on December 14, 2016:

Thanks, Genna. I appreciate your comment. I share your opinion, too. There is so much that we can learn from nature.

Genna East from Massachusetts, USA on December 14, 2016:

Alicia, your articles are so interesting, unusual, well-researched and presented. I always learn something new. I found this passage especially surprising:

"Acorn worms are marine animals that have an impressive ability to replace lost body parts. Surprisingly, humans have many of the same genes as the worms, including most—and perhaps all—of the ones involved in regeneration. For an unknown reason, the regeneration pathway isn't active in us. If we could find a way to stimulate the correct genes, it might be possible for humans to regrow lost body parts."

We can learn so much from nature.

Linda Crampton (author) from British Columbia, Canada on December 14, 2016:

Thank you very much for the comment, MsDora. I agree—the acorn worm does deserve some respect!

Dora Weithers from The Caribbean on December 14, 2016:

The acorn worm deserves some respect. Hope they will one day show us how to regenerate like they do, since we have the capability. Awesome facts in an excellent presentation.

Linda Crampton (author) from British Columbia, Canada on December 13, 2016:

Thanks, Jodah. The gene similarity is definitely an amazing thought. I hope the study of acorn worms proves useful to humans.

John Hansen from Australia (Gondwana Land) on December 13, 2016:

This was amazing information, Linda. It's incredible that we share 70% of similar genes with the acorn worm and they are our closest invertebrate relative.

Linda Crampton (author) from British Columbia, Canada on December 13, 2016:

Thank you very much, Larry. It is an amazing process!

Linda Crampton (author) from British Columbia, Canada on December 13, 2016:

Hi, Bill. Yes, there is so much that we don't understand about nature. I think that it's a fascinating area of study. Thanks for commenting.

Larry Rankin from Oklahoma on December 13, 2016:

I've always been amazed by this process.

Terrific read!

Bill De Giulio from Massachusetts on December 13, 2016:

Hi Linda. Amazing. Nature never ceases to amaze me. Clearly there is so much out there that we don't know or understand. Thank you for the education.

Linda Crampton (author) from British Columbia, Canada on December 13, 2016:

Thanks, Bill! I appreciate your visit and comment.

Bill Holland from Olympia, WA on December 13, 2016:

Absolutely fascinating, Linda! Seriously cool stuff!

Linda Crampton (author) from British Columbia, Canada on December 13, 2016:

Hi, Flourish. Yes, some lizards can regenerate their tails. It's a shame that we don't have a better ability to regenerate body parts. Thank you very much for the comment.

Linda Crampton (author) from British Columbia, Canada on December 13, 2016:

Hi, Buildreps. Yes, those are interesting puzzles! Thank you for the visit and comment.

FlourishAnyway from USA on December 13, 2016:

Holy Moses how neat! Patty mentioned the rat's toe. Are there vertebrates that have this ability? Seems like I recall growing up these little black striped lizards in South Carolina sometimes had part of their tails missing (often due to our cats) and they grew them back. You have such fascinating topics!

Buildreps from Europe on December 13, 2016:

Very interesting article, Alicia. For me is the most interesting question why and where in the evolutionary process the ability to regenerate was shut off. Like you say it's also wondrous how a creature that shares so much similar genes with us looks so different.

Linda Crampton (author) from British Columbia, Canada on December 12, 2016:

Thank you very much for the comment, Jackie. I appreciate your visit. Life is certainly fascinating!

Jackie Lynnley from the beautiful south on December 12, 2016:

So very interesting. Kind of like no rhyme or reason but then that is the miracle of things like this. Shows us not everything is black or white and how uninteresting life would be if it were.

Yours are always an enjoyable read!

Linda Crampton (author) from British Columbia, Canada on December 12, 2016:

Hi, Patty. Yes, regenerative medicine is very interesting. It offers great hope for the future. Thanks for the interesting comment.

Patty Inglish MS from USA and Asgardia, the First Space Nation on December 12, 2016:

I love all this work in regenerative medicine, first hearing in Middle School that the French had been working with limb regeneration back in the 1940s. They removed a rat's paw and were able to grow back an entire toe. Poor rat, but the achievement was startling.