Acorn Worms and Regeneration of Human Body Parts

Updated on October 14, 2017
AliciaC profile image

Linda Crampton is a writer and teacher with an honors degree in biology. She loves to study nature and write about animals and plants.

A preserved acorn worm
A preserved acorn worm | Source

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 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. Scientists are studying worm and human genes with this goal in mind.

Acorn worms are not closely related to earthworms. Earthworms are invertebrates. Acorn worms belong to a group known as hemichordates. This group is related to another group of animals known as chordates. Humans and other vertebrates are chordates.

An Acorn Worm Digs in the Sand

The prefix hemi means half. Hemichordates could he thought of as half way between invertebrates and chordates. Acorn worms belong to the Phylum Hemichordata and the class Enteropneusta. Humans belong to the phylum Chordata.

Body 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 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. | Source

The Proboscis and Collar

The proboscis is a muscular structure that enables an acorn worm to dig its way through the sand or mud. It has no eyes, ears, or other structures that we might expect on the head of an animal. The skin of the entire worm contains sensory receptors, however. These probably enable the animal 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 | Source

The Trunk

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. There is a plexus (collection of branched nerves) under the skin cells. There is also a dorsal nerve cord and a ventral one. There is no brain, however.

The excretory organ is located near the heart and is known as the glomerulus or 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 the intertidal area or in 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 an acorn worm (Belanoglossus simodensis)
Lifecycle of an acorn worm (Belanoglossus simodensis) | Source

Reproduction

Acorn worms are either male or female. The female releases a mass of eggs covered with mucus. The male releases sperm. Once the sperm fertlizes 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 in Acorn Worms: A UW Video

Regeneration Abilities

Researchers at the University of Washington (UW) recently 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 tell the regenerated worms from the original worm. 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.

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

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.

Another View of a Deep Sea Acorn Worm

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.

A Microscopic Acorn Worm Under a Microscope

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, however. Regeneration of body parts could have a dramatic effect on human lives.

References

Exploration of the hemichordata and the acorn worm in a virtual lab from Rutgers University

Regeneration in acorn worms and humans: A news release from the University of Washington

The growing scientific interest in hemichordates plus facts about the animals from The Node (The Company of Biologists)

Questions & Answers

© 2016 Linda Crampton

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    • AliciaC profile imageAUTHOR

      Linda Crampton 

      11 months ago from British Columbia, Canada

      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 profile image

      Jackie Lynnley 

      11 months ago from The Beautiful South

      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!

    • AliciaC profile imageAUTHOR

      Linda Crampton 

      13 months ago from British Columbia, Canada

      I think so, too, jacksonkirk!

    • profile image

      jacksonkirk 

      13 months ago

      omg so cool

    • AliciaC profile imageAUTHOR

      Linda Crampton 

      14 months ago from British Columbia, Canada

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

    • k@ri profile image

      Kari Poulsen 

      14 months ago from Ohio

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

    • AliciaC profile imageAUTHOR

      Linda Crampton 

      17 months ago from British Columbia, Canada

      Thank you very much, Sara.

    • Sara Krentz profile image

      Sara Krentz 

      17 months ago from USA

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

    • AliciaC profile imageAUTHOR

      Linda Crampton 

      23 months ago from British Columbia, Canada

      Thank you very much for the kind comment, Demas.

    • profile image

      Demas W. Jasper 

      23 months ago

      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.

    • AliciaC profile imageAUTHOR

      Linda Crampton 

      23 months ago from British Columbia, Canada

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

    • teaches12345 profile image

      Dianna Mendez 

      23 months ago

      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.

    • AliciaC profile imageAUTHOR

      Linda Crampton 

      23 months ago from British Columbia, Canada

      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.

    • profile image

      Suhail and my dog K2 

      23 months ago

      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.

    • AliciaC profile imageAUTHOR

      Linda Crampton 

      23 months ago from British Columbia, Canada

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

    • annart profile image

      Ann Carr 

      23 months ago from SW England

      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!

      Ann

    • AliciaC profile imageAUTHOR

      Linda Crampton 

      24 months ago from British Columbia, Canada

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

    • Genna East profile image

      Genna East 

      24 months ago from Massachusetts, USA

      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.

    • AliciaC profile imageAUTHOR

      Linda Crampton 

      24 months ago from British Columbia, Canada

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

    • MsDora profile image

      Dora Weithers 

      24 months ago from The Caribbean

      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.

    • AliciaC profile imageAUTHOR

      Linda Crampton 

      24 months ago from British Columbia, Canada

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

    • Jodah profile image

      John Hansen 

      24 months ago from Queensland Australia

      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.

    • AliciaC profile imageAUTHOR

      Linda Crampton 

      24 months ago from British Columbia, Canada

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

    • AliciaC profile imageAUTHOR

      Linda Crampton 

      24 months ago from British Columbia, Canada

      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 profile image

      Larry Rankin 

      24 months ago from Oklahoma

      I've always been amazed by this process.

      Terrific read!

    • bdegiulio profile image

      Bill De Giulio 

      24 months ago from Massachusetts

      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.

    • AliciaC profile imageAUTHOR

      Linda Crampton 

      24 months ago from British Columbia, Canada

      Thanks, Bill! I appreciate your visit and comment.

    • billybuc profile image

      Bill Holland 

      24 months ago from Olympia, WA

      Absolutely fascinating, Linda! Seriously cool stuff!

    • AliciaC profile imageAUTHOR

      Linda Crampton 

      24 months ago from British Columbia, Canada

      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.

    • AliciaC profile imageAUTHOR

      Linda Crampton 

      24 months ago from British Columbia, Canada

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

    • FlourishAnyway profile image

      FlourishAnyway 

      24 months ago from USA

      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 profile image

      Buildreps 

      24 months ago from Europe

      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.

    • AliciaC profile imageAUTHOR

      Linda Crampton 

      24 months ago from British Columbia, Canada

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

    • Jackie Lynnley profile image

      Jackie Lynnley 

      24 months ago from The Beautiful South

      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!

    • AliciaC profile imageAUTHOR

      Linda Crampton 

      24 months ago from British Columbia, Canada

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

    • Patty Inglish, MS profile image

      Patty Inglish MS 

      24 months ago from USA. Member of Asgardia, the first space nation, since October 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.

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