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Myxozoa: Pushing the Limits of Definitions (LSP #214)

Myxozoa: Pushing the Limits of Definitions (LSP #214) October 18, 2021

Hi and welcome back! I’ve been a bit under the weather lately, but I had to show you this: We’ve found a critter unlike any other on the planet. Myxozoa lacks something that every other animal-classed creature on Earth has. And that lack is helping us redefine life itself. Today, Lord Snow Presides over a discovery about myxozoa that might just change a lot of what we think we know about biology.

endless discovery awaits
(Robert Linder.)

(I ran into this topic because I got really curious about the earliest stages of human gestation earlier today. One science link led to the next, and here I am: mind-blown, with no idea how I got here.)

Everyone, Meet Myxozoa of the Cnidarians.

(Tell me. Just try to tell me that doesn’t sound like the most-metal-af name evar for a science-fiction villain. Go ahead. I’ll wait.)

Life on Earth typically gets divided up into kingdoms. Scientists keep dividing all that life in different ways according to how each group organizes itself. Most authorities recognize 5-7 kingdoms. (Encyclopedia.com says 5, while noted biologist Thomas Cavalier-Smith leaned toward 7 as of 2015.)

As a phylum, cnidarians land in kingdom Animalia. All 11k species of cnidarians are water-dwellers (salt or fresh; they’re chill either way). Some cnidarians, like jellyfish, swim freely. Others, like coral, remain fixed in place most or all of their lives. Their name comes from special cells they have called cnidocytes. Cnidarians use these cells to sting their food and defend themselves from attacks.

And myxozoa is a cnidarian. But they aren’t like the other cnidarians. Instead, they’re parasites that spend part of their lives inside fish. There, they can do a lot of damage to commercial fish like salmon (here’s a very gross example).

Myxozoa is a really, really tiny cnidarian.

Not only is myxozoa the smallest cnidarian, it’s also the smallest animal to have ever lived, ever, on Earth. This parasite ranges in size from 10 μm (micrometers) as a spore, which works out to 0.000393701″, all the way to 2 millimeters when grown. Sometimes their whole bodies comprise just a few cells.

And that’s not even the weirdest thing about these critters.

How Myxozoa Lost Its Groove.

We’ve known about this tiny little myxozoa subphylum for a while now. But biologists didn’t fully classify them as cnidarians until 2007. For a long time, biologists thought they were protozoans (probably because of the parasitic thing and their size). Further research revealed that they were actually part of the cnidarian phylum. But whoa nelly, are they ever different from the usual cnidarian!

You see, myxozoa does not have mitochondrial respiration. It lives anaerobically, having completely lost that entire part of its genetic code. And that’s confusing in a lot of ways. Animals use mitochondrial respiration. It’s a very efficient process that allows animal life to convert oxygen into ATP (adenosine triphosphate), which all life uses as energy. And it works through, you guessed it, our mitochondria.

Well, myxozoa doesn’t have any of that stuff. Instead, these parasites have some organelles in their cells that look related to mitochondria, but the process of evolution has stripped away the genes that handle the creation of mitochondria — and thus all the code that handles aerobic respiration. (Sources indicate that myxozoa probably evolved in an environment really low on oxygen — like, well, fish innards.)

That is incredible. 

Some single-celled lifeforms and bacteria are anaerobic. We know that.

But myxozoa is an animal.

A Weird, Weird Critter.

In 2020, a peer-reviewed paper described how biologists figured out how myxozoa lost those genes. They actually figured out how myxozoa went from a basic free-floating cnidarian to a parasite, losing a bunch of its genes in the process.

And this reminds me of news stories some years back about how some RNA-based viruses used to be DNA-based. We used to think that cells started as RNA (single-strand genetic code), using ribose, and then evolved to use two strands that used 2-Deoxyribose. But then, we found some viruses that had evolved downward from DNA to RNA, that maybe the two kinds of genetic codes had existed together from the very beginning, and that maybe DNA itself was just another kind of RNA.

This whole topic — whew, it’s a rabbithole.

  • “Giant viruses may have evolved from cellular organisms, not the other way around” (Ars Technica, 2011)
  • “Could Giant Viruses Be the Origin of Life on Earth?” (National Geographic, 2014)
  • “Beyond coronavirus: the virus discoveries transforming biology” (Nature, 2021)

Then, later in 2020, another paper came out that described how myxozoa has also lost the ability to use a process called DNA cytosine methylation. That process handles a lot of life’s development, including changing how genes act, how animals develop and age, and even how mammalian fetuses develop before birth. (Things that can go wrong in this process: heart failure, premature aging, cardiovascular disease, and even cancer.)

I wonder what else myxozoa has found unnecessary through those long, long eons?

Causing the Best Ruckus.

Myxozoa is one bare-bones little animal. And yet it definitely is an animal, a firm and well-accepted part of the cnidarian family. What we’re discovering about it has the potential to change a lot of what scientists think about how life evolves — and what animals actually even are.

And y’all know what I’m thinking every single time I fall down one of these rabbitholes, right? I know you do:

Man alive, we’ve found ourselves another bad day to be a Creationist.

The sheer mind-blowing facts of our world never end. These rabbitholes we explore turn into warrens full of information for the curious to devour — and each new twist and turn in the warren only leads us to more questions we want to answer. At no time in human history has it been easier to learn and grow — and best of all, to share what we’ve found with others.

This process of discovery and answers and questions and observation will never end, either because human curiosity itself doesn’t end — unless, that is, it’s quashed by authority figures who require their followers’ obedience at all costs, which requires curiosity to die.

Those authorities want to teach their followers that life is simple to understand, easy to grasp. POOF! There it is! Send money now.

Reality is anything but. It’s a gorgeous technicolor riot, and the more we find out about it, the more tinny, silly, and distant those authorities’ demands seem.

Today, Lord Snow Presides over the triumph of the light of science over the darkness of religious zealots’ “demon-haunted world.”

NEXT UP: We’ll finally get to tackle that evangelism reset topic! See you Wednesday!


About Lord Snow Presides (LSP)

Lord Snow Presides is our off-topic weekly chat series. Lord Snow was my very sweet white cat. He actually knew quite a bit. Though he’s passed on, he now presides over a suggested topic for the day. Of course, please feel free to chime in with anything on your mind: there’s no official topic on these days. I’m just starting us off with something, but consider the sky the limit here. We especially welcome pet pictures!


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About Captain Cassidy
Captain Cassidy grew up fervently Catholic, converted to the SBC in her teens, and became a Pentecostal shortly afterward. She even volunteered in church (choir, Sunday School) and married an aspiring preacher! But then--record scratch!--she brought everything to a screeching halt when she deconverted in her mid-20s. That was 25 years ago. Now a comfortable None, she blogs on Roll to Disbelieve about psychology, pop culture, politics, relationships, cats, gaming, and more--and where they all intersect with religion. She lives with an adored and adoring husband named Mr. Captain and a sweet, squawky orange tabby cat named Princess Bother Pretty Toes. At any given time, she's running out of bookcase space. You can read more about the author here.

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