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Scientists discover first known animal that doesn't breathe

Spores of the parasite H. salminicola swim under a microscope. Those alien "eyes" are actually stinger cells, one of the few features this organism hasn't evolved away.
Spores of the parasite H. salminicola swim under a microscope. Those alien "eyes" are actually stinger cells, one of the few features this organism hasn't evolved away.
(Image: © Stephen Douglas Atkinson)

When the parasitic blob known as Henneguya salminicola sinks its spores into the flesh of a tasty fish, it does not hold its breath. That's because H. salminicola is the only known animal on Earth that does not breathe.

If you spent your entire life infecting the dense muscle tissues of fish and underwater worms, like H. salminicola does, you probably wouldn't have much opportunity to turn oxygen into energy, either. However, all other multicellular animals on Earth whose DNA scientists have had a chance to sequence have some respiratory genes. According to a new study published today (Feb. 24) in the journal Proceedings of the National Academy of Sciences, H. salminicola's genome does not. 

A microscopic and genomic analysis of the creature revealed that, unlike all other known animals, H. salminicola has no mitochondrial genome — the small but crucial portion of DNA stored in an animal's mitochondria that includes genes responsible for respiration.

Related: These bizarre sea monsters once ruled the ocean

While that absence is a biological first, it's weirdly in character for the quirky parasite. Like many parasites from the myxozoa class — a group of simple, microscopic swimmers distantly related to jellyfish — H. salminicola may have once looked a lot more like its jelly ancestors but has gradually evolved to have just about none of its multicellular traits. 

"They have lost their tissue, their nerve cells, their muscles, everything," study co-author Dorothée Huchon, an evolutionary biologist at Tel Aviv University in Israel, told Live Science. "And now we find they have lost their ability to breathe." 

The nucleus of each H. salminicola spore glows green under a fluorescent microscope. Through microscopy and genetic sequencing, the study authors learned that H. salminicola is the only known animal with no mitochondrial DNA. (Image credit: Stephen Douglas Atkinson)

That genetic downsizing likely poses an advantage for parasites like H. salminicola, which thrive by reproducing as quickly and as often as possible, Huchon said. Myxozoans have some of the smallest genomes in the animal kingdom, making them highly effective. While H. salminicola is relatively benign, other parasites in the family have infected and wiped out entire fishery stocks, Huchon said, making them a threat to both fish and commercial fishers.

When seen popping out of the flesh of a fish in white, oozing bubbles, H. salminicola looks like a series of unicellular blobs. (Fish infected with H. salminicola are said to have "tapioca disease.") Only the parasite's spores show any complexity. When seen under a microscope, these spores look like bluish sperm cells with two tails and a pair of oval, alien-like eyes. 

Those "eyes" are actually stinging cells, Huchon said, which contain no venom but help the parasite latch onto a host when needed. These stinging cells are some of the only features that H. salminicola has not ditched on its journey of evolutionary downsizing.

"Animals are always thought to be multicellular organisms with lots of genes that evolve to be more and more complex," Huchon said. "Here, we see an organism that goes completely the opposite way. They have evolved to be almost unicellular."

So, how does H. salminicola acquire energy if it does not breathe? The researchers aren't totally sure. According to Huchon, other similar parasites have proteins that can import ATP (basically, molecular energy) directly from their infected hosts. H. salminicola could be doing something similar, but further study of the oddball organism's genome — what's left of it, anyway — is required to find out.

Originally published on Live Science.

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  • TorbjornLarsson
    admin said:
    A genomic analysis of the creepy parasite H. salminicola reveals that the creature has no mitochondrial DNA and no way to breathe — two animal firsts.

    This parasitic 'blob' is the only known animal that doesn't breathe : Read more

    The paper is paywalled, but it seems myxozoan life cycles go through sexual actinospore stages and vegetative stages http://folia.paru.cas.cz/artkey/fol-200601-0001_myxozoan_genera_definition_and_notes_on_taxonomy_life-cycle_terminology_and_pathogenic_species.php ] and that we are looking at the latter being ~ 10 um https://fishpathogens.net/pathogen/henneguya-salminicola ].

    As a comparison human skin cells average ~ 30 um, so these "suckers" should have minimized the genome size that in turn typically decide cell size.
    Reply
  • SpinResistant
    Somewhat puzzling. What about anaerobic bacteria? Is the author of this article presuming that they are really aerobic, or that they aren't animals? They are certainly lifeforms and they contain no chlorophyll so they aren't plants. Seems like some effort is being made to make H. Salminicola look a lot uniquer than it actually is.
    Reply
  • CMAenergy
    admin said:
    A genomic analysis of the creepy parasite H. salminicola reveals that the creature has no mitochondrial DNA and no way to breathe — two animal firsts.

    This parasitic 'blob' is the only known animal that doesn't breathe : Read more
    OK Where are these parasites mainly found (bodies of water) and how do they affect the fish to where we can identify them, and how do they affect the human when eating fish with this parasite? Can humans get infected by this parasite?
    I have trouble comprehending all this above my intelligence, so please make it simple for me to comrhend
    Reply
  • NgNg
    Someone needs to take a freshman Biology course. Cellular respiration and "breathing" are NOT the same thing.
    Reply
  • Marble
    SpinResistant said:
    Somewhat puzzling. What about anaerobic bacteria? Is the author of this article presuming that they are really aerobic, or that they aren't animals? They are certainly lifeforms and they contain no chlorophyll so they aren't plants. Seems like some effort is being made to make H. Salminicola look a lot uniquer than it actually is.
    By "animals" they are referring the eukaryotes, which contain organelles like nuclei and mitochondria. Bacteria are prokaryotes. You are correct that bacteria do not contain mitochondria - an interesting evolutionary story unto itself. Google "mitochondria and bacteria ".
    Reply
  • androecium
    SpinResistant said:
    Somewhat puzzling. What about anaerobic bacteria? Is the author of this article presuming that they are really aerobic, or that they aren't animals? They are certainly lifeforms and they contain no chlorophyll so they aren't plants. Seems like some effort is being made to make H. Salminicola look a lot uniquer than it actually is.

    Bacteria are not animals - they're unicellular prokaryotes. This is a big exception to an otherwise universal rule. Pretty incredible, actually.
    Reply
  • TorbjornLarsson
    androecium said:
    Bacteria are not animals - they're unicellular prokaryotes. This is a big exception to an otherwise universal rule. Pretty incredible, actually.

    Yes, especially incredible considering the relatively recent false alarm of (10 times as large) Loriciferans from anoxic mud - who turned out to be dead specimens.

    There is no rule in biology without exceptions, including this one. (So there are some population genetics laws for equilibrium conditions, but outside of equilibrium ... well, the analogous conditions work as laws in thermodynamics so YMMV.)
    Reply
  • NgNg
    admin said:
    A genomic analysis of the creepy parasite H. salminicola reveals that the creature has no mitochondrial DNA and no way to breathe — two animal firsts.

    This parasitic 'blob' is the only known animal that doesn't breathe : Read more

    1) Myxozoans have been known for quite some time (the taxonomic Class was erected in the 1970s), and it has been known since they were first discovered that they have no mitochondria. Therefore, it has been known since soon after they were first discovered that they are obligate anaerobes.

    This would make them unique among Metazoans (i.e., animals). However, Myxozoans are rather odd Metazoans in the first place (in fact, for a long time they were considered protozoans). This is probably due to the the fact that they are obligate parasites (parasites are often very highly derived, and sometimes almost unrecognizable as members of their higher taxonomic groups). For instance, Myxozoans, although Cnidarians, were not recognized as such until about two decades ago.

    2) Cellular respiration and "breathing" are two different things. Cellular respiration is when glucose is metabolized. If that metabolization involves oxygen, it is considered aerobic respiration; if it doesn't utilize oxygen, it is considered anaerobic respiration. "Breathing" is the mechanical movement of air in and out of the body. The term can also be used to refer to the movement of oxygenated water over specialized gills. While both cellular respiration and "breathing" are called "respiration" they are NOT the same thing. There are many metazoans that do not breathe (or even have specialized gills). These organisms get their oxygen via simple diffusion over the body wall. In fact, this is true for most (all?) Cnidarians -- the Phylum to which Myxozoans belong. However, ALL living organisms have some sort of cellular respiration; in the case of Myxozoans that respiration is anaerobic.

    3) The cool finding here is that there are no remnants of mitochondrial genes in the Myxozoan genome. Since the phylogenetic of the Myxozoa indicates that they are derived from Cnidarians, and all other Cnidarians are aerobic, this is a bit puzzling. Normally one would expect there to be some remnants of disused genes, even if their initial deactivation was in the distant past.
    Reply
  • Stephen J. Bauer
    I never realized the diversity of the definition for an animal. It appears that any organism that is not classified as Plants, Fungi, Protista, Bacteria, or Archaea is an animal.
    Reply
  • GeoXXX
    NgNg said:
    1) Myxozoans have been known for quite some time (the taxonomic Class was erected in the 1970s), and it has been known since they were first discovered that they have no mitochondria. Therefore, it has been known since soon after they were first discovered that they are obligate anaerobes.

    This would make them unique among metazoans (i.e., animals). However, Myxozoans are rather odd metazoans in the first place (in fact, for a long time they were considered protozoans). This is probably due to the the fact that they are obligate parasites (parasites are often very highly derived, and sometimes almost unrecognizable as members of their higher taxonomic groups). For instance, Myxozoans, although Cnidarians, were note recognized as such until about two decades ago.

    2) Cellular respiration and "breathing" are two different things. Cellular respiration is when glucose is metabolized via oxidative reactions. "Breathing" is the mechanical movement of air in and out of the body. The term can also be used to refer to the movement of oxygenated water over specialized gills. While both are called "respiration" they are NOT the same thing. There are many metazoans that do not breath (or even have specialized gills), and get their oxygen via simple diffusion over the body wall. In fact, this is true for most Cnidarians -- the Phylum to which Myxozoans belong.

    3) The cool finding here is that there are no remnants of mitochondrial genes in the Myxozoan genome. Since the phylogenetic of the Myxozoa indicates that they are derived from Cnidarians, and all other Cnidarians are aerobic, this is a bit puzzling -- normally one would expect there to be some remnants to disused genes, even if their initial deactivation was in the distant past.
    I enjoyed your informative answers, I learned a lot! You are one smart raccoon 🦝!
    Reply