Pyrosomes: Strange and Bioluminescent Creatures in the Ocean

Updated on February 24, 2020
AliciaC profile image

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

A photo of a bioluminescent pyrosome taken off the coast of East Timor
A photo of a bioluminescent pyrosome taken off the coast of East Timor | Source

What Is a Pyrosome?

A pyrosome is a strange, gelatinous, and bioluminescent creature that is found in the ocean. It's actually a colony of marine animals known as tunicates. Pyrosomes have fascinated observers for a long time. The interest in the creatures has recently increased due to a mysterious population explosion on the west coast of the United States and Canada. The unexplained pyrosome bloom reached its peak in the summer of 2017.

Tunicates are sac-like marine invertebrates. In free-living tunicates, the sac has two tubes at the top through which water enters and leaves the animal. The animal filters plankton out of the water, which also supplies it with oxygen.

Despite their relatively simple body as adults, tunicates have features which show that they are related to vertebrates. The individual tunicates in a pyrosome can be seen in the photo above. A pyrosome colony ranges from around a centimetre in length to ten metres long.

Pyrosomes are sometimes referred to as comb jellies or salps, but neither of these terms is correct. Comb jellies are gelatinous animals which have rows of cilia (the "combs") that are used for swimming. Salps are gelatinous tunicates that start their lives as free living organisms but later link together to form chains.

A Beautiful Example of a Pyrosome

The free-living tunicates discussed in this article are ascidians (members of the class Ascidiacea). They are the most common type of tunicates. Pyrosomes are thought to be related to ascidians.

Golden or ink-spot sea squirt (Polycarpa aurata)
Golden or ink-spot sea squirt (Polycarpa aurata) | Source

What Are Tunicates?

The tunicates that make up a pyrosome colony belong to the phylum Chordata, just as vertebrates do. Vertebrates belong to the subphylum Vertebrata, however, while tunicates belong to the subphylum Tunicata (or Urochordata).

Tunicates are frequently known as sea squirts. When a tunicate is touched, it often contracts, squirting out seawater in the process. The sac-like body of the animal is covered by a firm but flexible layer known as a tunic. The tunic is unusual because it contains cellulose, which is a molecule in plant cell walls. Tunicates are sessile, or attached to a surface and unable to move from place to place.

Internal anatomy of an ascidian tunicate
Internal anatomy of an ascidian tunicate | Source

Internal Anatomy and Physiology

Tunicates are filter feeders. Seawater enters the branchial siphon of an ascidian tunicate and travels into the sieve-like branchial basket, where food is trapped. The terminology can be confusing because there are multiple names for the body parts. The branchial siphon is also known as the oral, bucal, or incurrent siphon. The branchial basket is also known as the pharyngeal basket. The slits on the basket are sometimes known as gill slits.

The tunicate feeds on the tiny plants and animals found in seawater and collectively known as plankton. The plankton is trapped by the mucus made by the endostyle in the branchial basket. It's then transported to the stomach and moved from there to the intestine. After digestion has been completed and nutrients extracted from the food, feces leaves the tunicate's body through the atrial or excurrent siphon.

Oxygen from the incoming seawater is absorbed by blood vessels in the branchial basket. Carbon dioxide waste made by the animal is released through the excurrent siphon.

A cerebral ganglion is located between the siphons and plays the role of a very simple brain. The animal has a heart, which periodically reverses the direction in which it pumps blood. It also has both male and female reproductive organs and is therefore a hermaphrodite.

Anatomy of a larval ascidian tunicate
Anatomy of a larval ascidian tunicate | Source

The Ascidian Larva

The larva of an ascidian looks somewhat like a tadpole. It's sometimes referred to as the "ascidian tadpole larva", though it's not an amphibian like true tadpoles. It has features identical or similar to those of vertebrates, however, including:

  • a dorsal nerve cord along its back
  • a flexible rod under the nerve cord called a notochord (which is present in human embryos but is eventually replaced by the spine)
  • a cerebral vesicle, which resembles the area where the vertebrate brain develops
  • an eyespot or ocellus in the cerebral vesicle, which detects light and has similarities to the vertebrate eye
  • a statocyst in the cerebral vesicle, which is used for balance and orientation with respect to gravity; vertebrates have a similar structure called an otolith in their inner ear

The ascidian larva maintains its form for a maximum of only a few days. It has no mouth and doesn't feed. Its purpose seems to be to find a suitable habitat for the adult form. The larva sticks to a rock, shell, or other solid surface head first. It then digests its tail and other structures (including the ones that are similar to those of vertebrates) and makes new structures to form the adult body. The regeneration abilities of the animal are impressive. They may help researchers to understand and even improve regeneration in the human body.

Although the video below uses the word "worm" in its title, it's actually showing pyrosomes.

The Pyrosome Colony

Pyrosomes are still mysterious creatures. There is a lot that is unknown and puzzling about their biology. Some facts have been discovered, however.

The individual animals in a pyrosome are known as zooids. They are tunicates but are very small in size. The colony generally resembles a thimble in shape. The one in the photo at the start of this article is about a centimetre long. Some colonies are much longer than an adult human and have an opening large enough for a person to enter. There may be hundreds, thousands, or even hundreds of thousands of zooids in a particular colony.

The zooids are connected by tissue. Some form of communication between them exists because they can coordinate their behaviour. When one zooid emits light in bioluminescence, they all do, for example.

Though pyrosomes are sometimes said to drift through the ocean, they do have a weak power of propulsion. The incurrent opening of the zooids faces the ocean, but the excurrent opening faces the cavity inside the "thimble". When the zooids release water after extracting food and oxygen, it flows out of the opening of the pyrosome. This produces a slow form of jet propulsion.

The zooids reproduce asexually to produce identical zooids that enlarge the colony. They reproduce sexually to produce a group of cells that gives rise to a new colony.

Pyrosome is derived from the Greek pyro for “fire” and soma for “body.”

— Newsweek


The bioluminescence of pyrosomes is unusual compared to that shown by other animals. The blue-green light is often sustained instead of being emitted in pulses. Due to the lack of research about pyrosomes, the scientific paper that is often quoted in reference to their bioluminescence was published long ago in 1990. The authors reference even older research in their paper. The information may well be correct, but it would be nice to have additional and more recent studies to confirm it.

According to the research, the zooid has two light organs, one on either side of the incurrent siphon. The organs are reportedly triggered by touch or—unusually for bioluminescent animals—by light.

In many other bioluminescent animals, the light is known to be emitted when an enzyme called luciferase acts on a protein named luciferin. Bacteria live in some light organs and are responsible for this reaction. Bacteria have been found in the light organs of pyrosome zooids and luciferase has been found in their bodies. It hasn't yet been proven that the bacteria are making the luciferase or are responsible for the light production, however.

The woman in the video below talks about the "mouth" of the creature that she's found. She later discovered that the creature was a pyrosome and that the opening wasn't a mouth.

There were reports of some pyrosomes in 2014, and a few more in 2015 but this year there has been an unprecedented, insane amount.

— Olivia Blondheim, University of Oregon, in 2017

A Population Explosion

The unexplained population explosion of pyrosomes off the west coast of North America in 2017 is puzzling. The creatures were discovered in California, Oregon, Washington, British Columbia, and even Alaska. Their population was sometimes so dense that commercial fishing wasn't possible.

The bloom primarily consisted of a species known as Pyrosoma atlanticum. (The pyrosome is given a scientific name as though it were an individual even though it's really a colony of animals.) The physical appearance of the pyrosome is shown in the video above and the photo below. Its length ranges from 5 cm all the way up to 60 cm. Its body is pale orange, pink, or blue-pink in colour. It has been described as having a "pimply" appearance. It dries out and becomes flat if it's out of the water for too long. The species is sometimes known as a sea pickle.

Pyrosoma atlanticum is usually found in warmer water than that found off the British Columbia coast. A scientist at the Institute of Ocean Sciences in Sidney, British Columbia, suspects that the creatures became stuck in an unusually warm current that developed in the eastern Pacific between 2014 and 2016. In May 2017, a research team from Oregon collected 60,000 pyrosomes after only five minutes of trawling with a net. The pyrosomes filled fishing nets, stopping other creatures from being caught.

A major concern related to pyrosome blooms is that the zooids eat the zooplankton (tiny animals) that are eaten by other creatures. These creatures include shrimp, crabs, and the crustaceans that are an important food source for fish and seabirds. Yet another potential problem is that if an environmental change causes all of the pyrosomes created in a bloom to die at around the same time, their decomposing bodies might create serious effects for the ecosystem.

Pyrosoma atlanticum in a tidal pool in California
Pyrosoma atlanticum in a tidal pool in California | Source

Pyrosomes are generally found in the upper layers of the water column but may occasionally be found lower down.

Learning More About Pyrosomes

At the moment, pyrosomes aren't considered to be an invasive species in British Columbia. The bloom that peaked in 2017 seems to be over. If another one occurs, however, the status of the creatures may change.

Pyrosomes are fascinating and intriguing creatures. It would be very interesting to know more about how the zooids in a colony communicate with each other and about how they coordinate their behaviour. It would also be interesting to know exactly why their population explodes and what the consequences of this explosion might be.

We need to learn more about the biology and ecology of the creatures in case another bloom occurs. Solving the mysteries of their existence would probably be a great addition to our knowledge about life on Earth.


  • Tunicate and pyrosome information from ScienceDirect
  • Similarity of the ascidian tadpole larva ocellus or eyespot to the vertebrate eye from the NIH (National Institute of Health)
  • Pyrosome bloom facts and photos from National Geographic
  • Millions of pyrosomes appear on the coast of British Columbia—an article from the CBC (Canadian Broadcasting Corporation)

Questions & Answers

    © 2017 Linda Crampton


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      • AliciaC profile imageAUTHOR

        Linda Crampton 

        2 years ago from British Columbia, Canada

        Hi, Val. Thanks for the comment. Nature can certainly be mysterious as well as impressive. It gives us a lot to think about.

      • profile image


        2 years ago

        Linda---What a fascinating article! As a qigong practitioner and believer in energy medicine, I keep wondering about all strange aspects of bio-energy, and that started first with eels and their generating electricity.

        Then I watched a TV documentary with exactly the same kind of mysterious marine creatures emitting light that you are describing.

        I don't know about you, but every time I think of all these wonders of nature, I get this silly feeling that "something" is mocking the human intellect's limitations.

        Thank you for sharing it, my friend.

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        2 years ago from British Columbia, Canada

        Hi, Colin. I agree. It does make the mind boggle! Nature is fascinating.

      • escole61 profile image

        colin powell 

        2 years ago from march

        It makes the mind boggle. How much we still need to learn about life in our seas. It seems that we are discovering new life forms on a regular basis.

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        2 years ago from British Columbia, Canada

        That sounds like a beautiful experience, Dale. Thanks for sharing it.

      • GetitScene profile image

        Dale Anderson 

        2 years ago from The High Seas

        Hey interesting stuff. I kayak at night and often see twin vortexes of swirling, bioluminescent trails curling off of each paddle as I stroke my way over the water. Prettiest thing you can imagine.

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        2 years ago from British Columbia, Canada

        Thanks, Paul. No, I don't contribute to Wikipedia.

      • profile image

        Paul Venter 

        2 years ago

        Need your skills on Wikipedia.....or do you already contribute?

        Lovely bit of reading.....

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        2 years ago from British Columbia, Canada

        Thank you for the comment, Peg. I appreciate the share very much, too. Pyrosomes are certainly interesting. Their population explosion is puzzling.

      • PegCole17 profile image

        Peg Cole 

        2 years ago from Northeast of Dallas, Texas

        This is fascinating, in particular, the sea pickles showing up on that Oregon beach. Wonder what's up with that? And the photos and diagrams are amazing as well. These pyrosome creatures are strange but also fascinating. The videos were incredible; that weird tube thing, wow. Sharing this.

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        2 years ago from British Columbia, Canada

        Thank you very much for the kind and lovely comment, Rachel. I'm looking forward to reading more of your articles.

        Blessings to you as well.

      • Rachel L Alba profile image

        Rachel L Alba 

        2 years ago from Every Day Cooking and Baking

        Hello Linda friend, I haven't been visiting too much but missed your hubs so I checked them out. I am absolutely fascinated with sea creatures and was so happy to see your article on these above. I love the videos and I love seeing diagrams of the insides of them. Thank you for all your work on this hub.

        Blessings to you.

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        2 years ago from British Columbia, Canada

        I appreciate all your comments, Devika. Thank you very much for the visits.

      • profile image


        2 years ago

        Informative and you definitely share well-presented titles and with great research.

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        2 years ago from British Columbia, Canada

        Thank you very much for the kind comment, Alun. I appreciate your visit a great deal.

      • Greensleeves Hubs profile image

        Greensleeves Hubs 

        2 years ago from Essex, UK

        I vaguely remember Tunicates from school or university biology lectures, but the detail learned about them was exactly that - vague. They were obscure sea creatures I was never likely to encounter, and so were rapidly forgotten after finishing college.

        I can't however say that I have ever heard the name 'pyrosome' but they do seem an interesting and extraordinary looking group, and I'm sure the bioluminescence can make them spectacularly beautiful - the one in the opening photo looks like a glittering jewel.

        Just googled pyrosomes - unsurprisingly Linda, your article is better than any on the first page of the Google Search. Alun

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        2 years ago from British Columbia, Canada

        Hi, Jackie. The colours of some of the pyrosomes are lovely, though their local population explosion isn't! Ocean life is very interesting. I appreciate your visit.

      • Jackie Lynnley profile image

        Jackie Lynnley 

        2 years ago from the beautiful south

        So interesting and loved the Pyrosomes. Pink and blue, wow. Scary places with such beautiful sea life. Thank you for sharing this!

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        2 years ago from British Columbia, Canada

        Hi, Cynthia. Synchronicity is always an interesting experience! Thank you for commenting.

      • techygran profile image

        Cynthia Zirkwitz 

        2 years ago from Vancouver Island, Canada

        Wow, Linda, a little synchronicity is going on here-- we were driving home the other night alongside the Comox Harbour, admiring the full moon, when the topic of bioluminescence came up. I can now discuss this a little more knowledgeably, thanks to your well-written article.

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        2 years ago from British Columbia, Canada

        Thank you for such a nice comment, Chitrangada Sharan. I appreciate your visit.

      • ChitrangadaSharan profile image

        Chitrangada Sharan 

        2 years ago from New Delhi, India

        Such an informative, educational and interesting article! I thoroughly enjoyed going through the amazing information you provided about Pyrosomes.

        There is so much to know and wonder about in the ocean World. Most of us can only read about it .

        Thanks for sharing!

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        2 years ago from British Columbia, Canada

        Hi, Peggy. I hope that the pyrosome population explosion is an aberration, too. It could be a serious problem if it isn't! Thanks for the visit.

      • profile image

        Peggy Woods 

        2 years ago

        How interesting! I had not previously known anything about Pyrosomes. Hopefully it is an aberration that they are clogging up fishing nets and interfering with the fishing industry right now. Our world is truly an amazing place!

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        2 years ago from British Columbia, Canada

        Hi, Martie. Yes, some very unusual creatures share the Earth with us! They are fascinating to study. Thanks for the comment.

      • MartieCoetser profile image

        Martie Coetser 

        2 years ago from South Africa

        How fascinating! These mysterious bioluminescent marine animals are beyond my comprehension. They all seem to be alien, and yet we're sharing a planet with them.

        Thanks, Linda, for researching and sharing these amazing hubs about weird creatures :)

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        2 years ago from British Columbia, Canada

        Thank you so much, John. I appreciate your kindness.

      • Jodah profile image

        John Hansen 

        2 years ago from Queensland Australia

        This was a totally fascinating hub and as always informs and educates. Your articles never disappoint, Linda.

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        2 years ago from British Columbia, Canada

        Hi, Flourish. Yes, I agree—there is a lot that other organisms can teach us. A balance between different species is important, as you say. Thanks for the visit.

      • FlourishAnyway profile image


        2 years ago from USA

        We have so much to learn from the creatures around us! They have amped up survival of the fittest on so many levels. We should be careful of their ability to rapidly populate waters and crush out competing organisms.

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        2 years ago from British Columbia, Canada

        Thanks for the interesting comment, Dugitron9001.

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        2 years ago from British Columbia, Canada

        Hi, Heidi. I think you've raised an important point. It is fascinating to learn more about space, but we do need to learn more about our own planet as well. Cheers to you as well!

      • profile image


        2 years ago

        Puzzling to human understanding only.

      • heidithorne profile image

        Heidi Thorne 

        2 years ago from Chicago Area

        While I'm a strong proponent of space exploration, we still need to know so much more about the planet we inhabit! This is certainly an example of why. Thanks so much for always piquing our curiosity with your science posts! Cheers!

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        2 years ago from British Columbia, Canada

        Thank you very much for the comment, Dora. There's a lot to explore in the ocean. It's an amazing place.

      • MsDora profile image

        Dora Weithers 

        2 years ago from The Caribbean

        Fascinating indeed! A heart that pumps blood in the reverse and having two genders? Where have they been? Glad they are not harmful to people, although they're still a nuisance. Linda, you do have some interesting stories to tell.

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        2 years ago from British Columbia, Canada

        Thank you for the kind comment, Bill. I appreciate your visit very much.

      • billybuc profile image

        Bill Holland 

        2 years ago from Olympia, WA

        Such a fascinating world we live in. This was such an enjoyable article for a science geek like me. Thanks for the great information, Linda!

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        2 years ago from British Columbia, Canada

        Hi, Jill. Yes, there's lots to admire in tunicates! I appreciate your visit and comment.

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        2 years ago from British Columbia, Canada

        Thank you very much, Hari.

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        2 years ago from British Columbia, Canada

        I agree, Louise. There are so many wonders in the ocean. It's a fascinating place to explore.

      • The Dirt Farmer profile image

        Jill Spencer 

        2 years ago from United States

        A fascinating article! Tunicates were designed for survival, huh? A reversible heart AND both sets of reproductive organs. You have to admire that.

      • shprd74 profile image

        Hari Prasad S 

        2 years ago from Bangalore

        Comprehensive and very informative. Thanks Linda.

        - Hari

      • Coffeequeeen profile image

        Louise Powles 

        2 years ago from Norfolk, England

        There certainly is a lot of wonders in the ocean. The videos of the pyrosome is amazing. There is so much in the ocean we don't know about.


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