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July 6, 2024 47 mins

It is dark inside the human body, but not every denizen of the animal kingdom is such a closed book. In this classic episode of Stuff to Blow Your Mind, Robert and Joe discuss various creatures with transparent anatomical features and translucent bodies. (originally published 05/19/2022)

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Speaker 1 (00:06):
Hello, and welcome to Stuff to Blow Your Mind. My
name is Joe McCormick, and today we are bringing you
an episode from the Vault, an older episode of the show.
This one originally aired May nineteenth, twenty twenty two, and
it is called Creature with the Crystal Skin, about animals
that you can see straight through or see inside. I

hope you enjoy.

Speaker 2 (00:32):
Welcome to Stuff to Blow your Mind, a production of iHeartRadio.

Speaker 3 (00:41):
Hey, welcome to Stuff to Blow your Mind. My name
is Robert.

Speaker 1 (00:44):
Lamb and I'm Joe McCormick, and today we're going to
be talking about a biological topic which has fascinated me
for a while, ever since I was reading about a
family of frogs that I'm going to come back to
in a bit. And this is the idea of transparency
or translucency in animals, animals that have clear or at

least translucent skin or other body parts.

Speaker 3 (01:10):
Yeah, and just thinking about this topic brought me back
made me think about some stories that I probably haven't
read in about twenty years now, but the tales of
Fritz Lieber, a genre ryder who lived nineteen ten through
nineteen ninety two. A fun note, he was the son
of actor Fritz Lieber, so he's technically a junior to
his senior. Fritz Lieber Senior was in films like nineteen

thirty three's Phantom of the Opera starring Claude Rains, and
then Fritz Lieber Junior's son, Justin Lieber, was a philosopher
and a sci fi author in his own right.

Speaker 1 (01:43):
I think at some point I just popped open his
Wikipedia page and I saw there was a top line
reference to him also being, in addition to being like
a sword and sorcery author and science fiction author, a
chess expert. And that was one of those things where
I was like, is that real or is that just
like something that the author of them, say, elf, or
someone associated with them kind of snuck in there.

Speaker 3 (02:03):
I don't know. I'm not as as up on the
full Fritz Lieber biography there, but he wrote a lot
of stuff, various genre works. Some of his stories were
were also adapted into I think like a couple of
episodes of Night Gallery back in the day. But the closest,
the thing that's closest to my heart, the material that

I'm familiar with, are these stories he wrote about these
two characters Fofford and the Gray Mouser. So this is
your sort of iconic adventuring duo, and he's these stories
helped make it iconic. You have a pair, a barbarian
and a rogue and they get into all manner of adventures.
These were These were very popular stories. I think they
had an influence on the development of dungeons and dragons.

And they hold a pretty well too.

Speaker 1 (02:48):
Well. If it's a barbarian in a rogue, that sounds
like Conan and SUBATAI.

Speaker 3 (02:52):
Yeah, yeah, yeah, very much of that vein. So they're
great fun. They're always encountering various enemies and magic and
magical creatures. And in one work in particular, I believe
this is The Swords of Lankhma from nineteen sixty eight,
they encounter gules. Now I love goules, as they appear

in various other works of fiction, these guls are rather different,
and I think when I first read Fritz Leiber's Gules,
I was a little I wasn't that into them. I
was like, ah, this is a little too different from
what I'm used to. I just want bone chewing pallid humanoids.
Because he takes the idea in a rather different direction.

Speaker 1 (03:36):
Okay, so your standard gul is just a sort of
deathly looking humanoid who hangs out in graveyards and eats
grave flesh, right.

Speaker 3 (03:43):
Right, These gules have translucent anatomy. Essentially, they just look
like a walking skeleton because all of the soft tissues
in their bodies are transparent. So the only thing you
can actually see is the skeleton, unless like the light
is just right, because you know, it's not true and
it's not magical invisibility. It's supposed to be translucent tissue

based invisibility.

Speaker 1 (04:09):
So you would only see the skeleton. In most cases,
though there is more than the skeleton. They've got some fleshy,
soft squishy bits, but those just let the light pass
right through.

Speaker 3 (04:19):
Yeah, everything is see through except for the skeleton. So
I actually just want to read a little bit from
the Swords of Lackmar from nineteen sixty eight. After an
instant shock, Fawford realized that these must be ghoules, whose
flesh and inner organs he had heard with much skepticism,
but now no longer were transparent, except when the skin

became salily or rosalie, translucent on the genital organs or
on the lops and small breasts of their women. It
was said also that they ate only flesh human by preference,
and that it was strange, indeed, to watch the raw
gobbits they gulped, course down and churn within the bars
of their ribs, gradually turning to mush and fading from

sight as their sightless blood assimilated and transformed the food.
Granting that a mere normal man might ever have the
opportunity to watch ghules feast without becoming a supply of
gobbits himself. That is some pros. Yeah, yeah, he was
a good, good writer. There's a lot of fun and
whimsy too. So the Ghules in this story, they describe

themselves as being crystal fleshed, and they see it as
their sort of sacred responsibility to consume the flesh of say,
human beings, because our flesh is murkier, you know, it's
not that's translucent purity. So when they eat it, they
eat our flesh, it eventually becomes translucent, It becomes crystal

inside of them. There's a female Ghul that pops up
in these stories that I believe of Fawford actually ends
up falling for after a while, and she also has a.

Speaker 1 (05:57):
Great story about ghoul romance.

Speaker 3 (06:00):
Yeah, yeah, gool romance. But there's a bit where she's
talking about like the differences between between gules and humans,
and she tells him bones are beautiful, they are made
to be seen. And there's another part where Fauford is
asking questions about what's it like to be a ghoul
and he picks up on a bit of a scientific

critique that often comes up when discussing things like H. G.
Wells Invisible Man. He says, well, how can you see
anything if light passes right through you? He asked her
if ghules happen to see with the inside of the
back of their skulls, and she responds, quote, look closely
into my eyes, no, without getting between them and the fire.
Can you see a small rainbow in each That's where

the light is refracted to the seeing part of my brain,
and a very tiny real image formed there.

Speaker 1 (06:52):
I love alternative visual anatomy. That's great.

Speaker 3 (06:55):
Yeah. I love that he made sure to actually throw
that in there to address how his gules see anything.
But anyway, like I said, when I first read of
these creatures, I was like, oh, this is too different.
These are not gouls. I can really get behind But now,
as we're about to jump into the discussion of some
amazing natural world organisms that have various levels of translucency

to their bodies, I'm looking back on Fritz Lieber's ghules,
and I'm like, these are amazing, these ideas of these translucent,
fleshed beings like jumping into battle with their axes, and
to everyone on the other side, they just look like
skeletons because that's the only part that isn't see through.

Speaker 1 (07:35):
That is great. Okay, well, I guess the first example
of a real animal I want to talk about today
a group of animals actually known as the glass frogs.
And a little bit of terminology distinction. I guess we've
already said these words, but transparency versus translucency. If you're
not familiar, transparency you can think of as being clear

like glass, pretty much allowing all light to pass through,
whereas translucency you can think of, like frosted glass, is
allowing a lot of light to pass through, but not
as much as a total clarity.

Speaker 3 (08:10):
You'll find that these are those sometimes used interchangeably, even
sometimes in scientific papers. Though.

Speaker 1 (08:15):
Yeah, so, the so called glass frogs comprise many different
species but they all belong to the family Centralinidae, which
is found in regions throughout Central and South America. These
are mostly arboreal creatures, meaning they live in trees, often
in rainforests, and especially near sources of fresh water. So

if you want to find a glass frog, most of
the time a good place to look is like on
leaves overhanging the bank of a jungle stream. But if
you were to go out looking for one of these creatures,
you might have a bit of difficulty difficulty finding the frog,
even if you're looking right at the leaf where it's perched,

because glass frogs can blend in very well with foliage
and Rabbi attached a couple of pictures for you to
look at here of various green and yellow species of
glass frogs perched on a leaf. It's especially good to
look at like a leaf that's sort of lit from behind,
and the frog will be right next to a collection

of what looked like little semi transparent, semi opaque spherical globules,
and these are actually the frog's eggs. One of the
most striking things about the glass frog family is their skin. Now,
most species of glass frogs appear from above to have
a kind of moderately translucent skin, especially on some parts

of their dorsal sides, such as like the toes or
the legs, and so you can see the blurry specter
of bones in their toes or in their legs, which
is very creepy and very cool. This would be like
crystal ghules. You can actually see the bones through the skin.
Some species take this even further and have not only

semi translucent legs or parts of the backs, but nearly
totally transparent bellies. So this would be the belly the
ventral side. Again not all species, but with some it
can be almost as clear as glass, and you can
look through and see their internal organs in full color,
including a little tiny beating heart and a big thick

red artery going down the middle of the inside of
the stomach, a big coiled white mass of intestines, and
so forth.

Speaker 3 (10:35):
I mean they remind you of the visible man and
the visible woman anatomy kits. Yeah, I think we all
grew up with you know, where you have the plastics
see through skin and have you put all the little
organs in there. It's like this frog is meant to
be an anatomical education tool.

Speaker 1 (10:54):
Now, another feature only tangentially related to their transparence your translucency.
If you've ever seen the Planet Earth feature on glass frogs,
it includes at least one species of glass frog that
shows this amazing egg defense behavior. So with these frogs,
what will often happen is that there will be a

clutch of fertilized eggs sticking to the side of a
leaf that may be hanging above the water, and there
will be a father frog guarding the eggs. These eggs
are apparently a favorite food of local carnivorous wasps that
will kind of zoom in and try to munch on
them and pull a partially formed tadpole out of the

egg and take it away to eat it. But the
frog fathers actually defend their eggs literally by kicking the wasps,
which is amazing to watch. You should look up this clip.

Speaker 3 (11:50):
Yes I was watching this earlier, as is often the
case with Planet Earth footage. Very impressive, gorgeous to watch,
but it also really drives home how much the glass
frog looks like a clutch of eggs on the back
of that leaf.

Speaker 1 (12:05):
Yes, they often have marking or coloration patterns on their
backs that makes the adult male frog look like a
clutch of eggs itself, so it just kind of blends
in and then when the wasp gets close, it kicks.
One of the amazing things is seeing so it's this
tiny little frog. And a lot of these these frogs
are so small. They might be just a you know,

the size of the size of a fingertip, maybe a
couple of centimeters. I mean, they vary in size with
different species, but most of them are very small. But
then when you see that leg suddenly launch out like
a spring, it's like enormous. It's incredible how far it reaches.
But to come back to the glass element of the

glass frog, what is this translucent or in some cases
nearly transparent skin for why would it be of evolutionary
benefit to this frog to have parts of its body
being almost clear? Well, I think for a long time
it was presumed to have some kind of role in camouflage,

but we didn't really know for sure. But there was
a paper published in twenty twenty by James B. Barnett
at All in Proceedings of the National Academy of Sciences
called Imperfect Transparency and Camouflage in glass Frogs, And this
was really interesting. It did some experiments to try to
look at the translucent skin of a glass frog and

say what does it actually do in practice? Does it
work as camouflage and if so how? Now They start
by giving some background on biological camouflage in general. For example,
camouflage patterns on animals can help in multiple ways. They
say they can prevent both detection and recognition, so you
can imagine those as two slightly different things. Preventing detection

might mean that a predator doesn't notice you at all,
like they don't see that you're there, whereas preventing recognition
might mean that if the predator sees you, it doesn't
recognize you as what you are, maybe you look like
something else. And the authors mentioned that there are multiple
ways camouflage works. It can work by, say, matching a background.

There are lots of examples of this. But you can
think about a moth or a butterfly that has patterns
in coloration on its wings that resemble the patterns and
coloration of the bark of a treees it lands on
the tree, and it just kind of blends in. Another
thing would be mimicking particular background features, trying to recreate
textures that would exist in the background, and another thing

would be disrupting or breaking up edges trying to have
patterns that make it harder to tell where the outline
of an animal would be. But they raise an interesting question.
What if you're an animal that lives in a habitat
where you can't always predict in advance what kind of
background you will be the foreground of What if you're

a vulnerable creature that needs camouflage but you live in
a highly variable environment. Evolution has at least one solution
to this, which is active color change. So we've talked
about this on the show before, but think of octopuses
with their chromatophorre cells that allow them to shift colors
and blend in with seaweed or rocks or the sandy

floor of the ocean. There are tons of amazing videos
of this. You can look up where you wouldn't even
see it, Like a octopus just lands among some rocks
or some coral or seaweed or something and it just
becomes them. It's amazing.

Speaker 3 (15:35):
Yeah, I just almost a year ago I got to
observe an octopus in the wild in Hawaii, and yeah,
it got to watch it do this it was amazing,
like one of these situations where you watch it go
to some rocks or a bit of coral blend in,
and since you've been watching it, you can still make
out where it is. But if you move your eyes

away from it from just a set for just a
second and then come back, you can't see it anymore.
It's still there right in front of you. But the
camouflage is so perfect it's just quite amazing to behold totally.

Speaker 1 (16:10):
And another classic example one probably everybody's familiar with chameleons.
They can change colors to match background surfaces in order
to better blend in. But of course having something like
chromatophor cells evolving this capability is of course a very
niche evolutionary specialization, so you need that history feeding into it.

Is also of course biologically costly, and the authors point
out that the efficacy of active color change can actually
be limited by things such as the range of patterns available.
So an animal that can actively change its markings and
color patterns can't do that to an infinite degree of flexibility.

You know, it's still it's going to have surface features
and colors and like it can change somewhat, but can't
look like absolutely anything right right. And another thing is
the speed of change, so it takes a minute. You know,
you can see this even with octopuses that can change
very fast, but it still takes a few seconds sometimes.

So is there any other way to blend in with
your surroundings? Well, what about transparency. Transparency, of course has
the ability to create very high fidelity camouflage because you
can literally see through to the background. It can match
anything in the background. There's no limitation on the colors
or patterns available because you're just actually seeing the background,

and it works instantaneously. There's no time needed to change
if you just are transparent. Of course, there are difficulties
with transparency as well, but one example I might use
would be if you've ever seen pictures of this. There
is a butterfly known as the glass wing butter fly
that has you know, like all butterflies, it has large,

beautiful wings, but most of the surface of its wings
is actually transparent, like a pane of glass. It has
a sort of orange and black and white outline of
the wings, but most of the wings you can just
see right through them and they're not even reflective. They
don't cause a glare. I was watching a video about
this actually, and the glass wing Butterflies are able to

prevent their wings from being too reflective or shining back
with a glare by having these little tiny nano pillars
of wax on the surface of the transparent membranes that
sort of break up light patterns. I think kind of
like the way that you might have cones of foam
on the walls of a studio to break up the

reflection of sound waves. On this they would break up
the reflection of light waves with these tiny little wax
spikes all over the wings. Of course, you can't see
them because they're too small. Instead, it just looks like
clear glass.

Speaker 3 (18:58):
Yeah, these are weird to see in the wild because
it does look even as you're watching them fly around,
it looks like, well, something or something has come along
and just punch sections of their wing out. It's just
completely translucent.

Speaker 1 (19:11):
But the wings wouldn't work, of course, if they just
had holes in them. Instead, they actually had to evolve
layers of cells in their wings, thin layers of cells
that would allow light to pass right through and would
prevent the surface of the wings from picking up glare
from the sunlight. But also would still be solid enough
to work as wings.

Speaker 3 (19:30):
Yeah, they're sort of like Wonder Woman's invisible plane.

Speaker 1 (19:33):
Right, right, right, But I think it works for the
butterfly because the material of wings can be very thin, right,
it's a sort of thin. I believe it's made mostly
of kiten in this case, you know, kiten and cells
that can allow that to happen. It's going to be
harder to do with, say, like the thick, fleshy body

parts of something like a frog. And there are also
strategic limitations to camouflage via transparency, especially on land. Some
aquatic animals use transparency for camouflage, and we'll get more
into that in a bit when I know there's some
examples you wanted to talk about, rob but terrestrial animals
run into some different problems because on land, the author's

write quote, image distortion may be more obvious than in water,
and that kind of makes sense, right, It might be
easier to see the weird way that even a pretty
clear thing like a glass wing butterfly's wing still causes
a little bit of distortion in the background. It's not
as if there's nothing there, it's just remarkably clear for

an actual biological surface. Now, of course, glass frogs are
terrestrial animals. They make use of transparency or translucency, especially
pronounced in some species, and it is presumably a camouflage tactic,
but as I said earlier, we don't really know for sure,
or at least before this paper it was harder to know.
Is if it is a camouflage tactic, how exactly does

it work, and does it work at all? Could that
be empirically verified? And especially given some strange features such
as the fact that that in the ones that are
very clear, the really clear part of the skin is
usually on the ventral side, the belly side, and that's
the part that would be facing down to the surface

that they're perched on. More often they tend to have
some dorsal pigmentation, so on the back they might have
sort of green and yellow color patterns. You can see
they're not totally clear on the back. And so the
authors of this twenty twenty paper did a number of
different experiments contained within it to try to figure out
what was going on with these frogs. So they like
simulated the vision of predators that prey on the frogs

in the lab and looked at frogs with differing levels
of translucency or opacity to see if it made a
difference for those predators. They also tested it just with
humans looking at them to see if there were differences
in detect or recognition times based on how translucent or
opaque the frog is. And then they also performed an

experiment in the wild with simulated frogs. They like made
fake glass frogs out of gelatine with different levels of
opacity versus translucency to see if it affected predation. And
what these experiments found was that the quote perceived luminance
of the frogs was the big thing that really changed,

and it changed depending on the background compared to opaque frogs.
So I think one of the really important things to
understand here is that the translucency of the glass frog
doesn't actually change the color of the frog very much.
I mean, it's basically most of them have some kind
of green or green yellow coloration pattern and that pretty

much stays the same. What actually changes is the amount
of light that is allowed to pass through the frog
and specifically parts of the frogs such as the outlines
of the toes and the legs, and the transparency of
these frogs actually did help them blend in with the background,
especially when they're you know, they're on something like a leaf,

and it will allow light to pass through their bodies
in a manner consistent with the leaf underneath, especially at
the edges where their legs are meeting the surface. And
they did find ecologically that this level of transparency did
increase survival. So the frogs that let more light through
their skin got preyed on by birds less. Now coming

to I mentioned the legs, They say that the legs
made the biggest difference here. They said it was the
legs quote which surround the body at rest and create
a diffuse transition from background to frog luminance, rather than
a sharp, highly salient edge. So I think that's the
important way to think about this. What does the glass

frog's translucent skin do. It doesn't make frog invisible, and
it doesn't necessarily change the color of the frog. Instead,
what it does is it sort of erases the outline
of the frog instead of a sharp line of color
change or high contrast between the frog and its background. Instead,
there's a gradual, soft transition from background to frog because

the frog's skin allows that light to pass through and
this is a camouflage strategy they call edge diffusion. The
real purpose is to take away your body's outline.

Speaker 3 (24:33):
I like that, Yeah, I mean you see that in
various military camouflage designs as well, And it always makes
me think of have you ever seen these examples of
playing cards from World War Two? Where each playing card
has the outline of a different enemy aircraft on it,
The idea being that it'll sort of while I guess

the soldiers are sent around playing cards, they'll also end
up boning up on what p cular enemy aircraft look like,
what their outlines look like in the sky, so they
can identify them. So, you know, it's it would be
kind of like, then, okay, if we have the basic
outline of the of the airplane in people's minds, well,

what can we do to break up that outline so
that it's not instantly identifiable? Because whether you're talking about
animals or you're talking about in a natural environment, or
you're talking about humans in a military situation, it's like
seeing something identifying something and then comes whatever the action is.
And if you can break up that chain of reactions,

then you can buy yourself some time.

Speaker 1 (25:39):
Right, and the outline is incredibly important for that recognition component.
Like Robigan, you can look at these pictures I attached
near the top of this section here, both of which
are of glass frogs perching on a green leaf that's
being sort of brightly lit or lit from behind. And
in both cases, actually, no matter which direction the LA

sources coming from, the soft, diffuse edges of the frog
really do help it kind of look more just like
a kind of spot sun a leaf or something.

Speaker 3 (26:11):
Yeah, Like I mean, both of these cases, it's the
frog is pictured next to a pile of the eggs,
and like I say, the frog looks more like a
pile of eggs than a frog. It looks more like
you know, you look at it, and you're more likely
to say, what is that weird jelly shape? Oh, it's
a frog, as opposed to instantly identifying a frog. It
just throws you off, even for even just a fraction

of a second. And this is in a case where
we know what we're looking at. It's supposed to be
a picture of a frog.

Speaker 1 (26:38):
Yeah, And sometimes a fraction of a second is all
you need. Maybe if you're trying to avoid the gaze
of a bird that's passing by, or a wasp that's
passing by, or.

Speaker 3 (26:47):
Something trying to kick a wasp in the face, that
sort of thing.

Speaker 1 (26:49):
But as I mentioned a minute ago, while the use
of translucency or transparency in animals is somewhat rare on land,
it's actually more common in the water, and there are
some amazing examples in marine organisms.

Speaker 3 (27:06):
That's right. Yeah, there are a number of examples that
I think line up quite well with camouflage, and in
all cases, I guess it helps to be kind of small.
The smaller you are as an organism, the easier it's
going to be to have some sort of translucency or
transparency to your body. That being said, there are some
very large jellies, you know, they take up a fair

amount of space that of course are to varying degrees translucent.
But this is why the chances of actually seeing something
like one of Fritz Leiber's ghoules, or say a translucent
elephant are pretty slim. But yeah, there are a lot
of creatures in the sea that match up with this.
You have things like glass octopi and so forth. But yeah,

there are also just some really strange fish in the sea.
There are so many strange fish in the sea that frankly,
not being a strange fish is a bit strange. And
one of the stranger fish that you'll likely see is
an image of the barrel eye fish Macropinna microstoma. So
I think a lot of you've probably seen this image before.
And if you were to look up Macropinna microstoma or

just look up barrel eye, you'll see the one or
two famous images of this fish. It's a fish so
strange that you'll likely say, well, where does the fish
get off looking so strange? And then hearing you, this
fish will gaze at you with its two tubular eyes
staring straight through the translucent, fluid filled shield that composes

the upper portion of its head. This is just a
bizarre and I think oddly kind of cute looking fish
at least, like I say, there are a couple of
photographs that are out there just all over the place,
because this one really tore up the nature blogs years ago,
and even I think you're less scientifically inclined boards and

so forth, we're like, what is this? Look at the
strange creature? How can this be?

Speaker 1 (29:03):
You know what it reminds me of, is I had
to look up the name of this because I didn't
know what it was called. But the you remember those
glass balls they would have in like Worlds of Wonder
or something with the electricity inside. Yeah, it's apparently called
a plasma globe or a plasma lamp.

Speaker 3 (29:19):
Yeah, it looks kind of like a plasma lamp for sure.

Speaker 1 (29:22):
Yeah. So it's like a it's like a clear glass ball,
and then inside it'll be filled with some kind of
noble gas, I don't know, neon or something, and then
it will have a high voltage electrode in the middle.
And I guess what when you touch the you touch
the glass, it sort of like tries to jolt out
at you.

Speaker 3 (29:40):
Mm hmm.

Speaker 1 (29:41):
Well that's what this fish's head looks like. You're just
looking in at I don't know if that's brains or
what it's. It looks like plasma.

Speaker 3 (29:48):
Yeah, this this creature is so to be clear, most
of this fish is not translucent or transparent, but the
top of the head is, and inside you see primarily
these two big tubular type globes, and these are the
creature's eyes. So I'll get back in a second to
what this means. But this creature is the only known

member of their genus, but they are part of the
barrel eye family Opisto Proctadae, home to the spookfishes as
they're called with that all have these weird tubular telescoping eyes. Now,
these deep sea creatures have eyes like this, so they
can look, they can lock into a vertical position, but
they can also scan the depths above for possible prey.

So I imagine yourself living kind of deep, but you're
also concerned with the lighter regions of the ocean above
you because that's where potential food is. So you need
to be able to look straight up while yourself remaining
in a horizontal position, and so that's what they've evolved
to do. But then they can also direct them forward

as well, obviously to aid in such forward facing ventures
as say, actual eating the prey or dealing with things
that are happening on your level of the ocean. But
all these other tubular eyed spookfishes, they do not have
this strange translucent head situation going on. This is something

that we find particularly in the macropenum microstoma, and I
was reading about them in a paper. This was published
in the journal Coopia it's by authors Robinson and Rizin Bitchlar,
and it's titled Macropenum Microstoma and the Paradox of its
Tubular Eyes. So I want to read. I want to

read just a quote from this quote. The most striking
aspect of these fishes, when first viewed in situ, is
the transparent, cowl like shield that covers the top of
the head and the prominent tubular eyes. Within the shield
is a tough, flexible integument that attaches to dorsal and
medial scales behind the head and to the broad, transparent

subocular bones that protect the eyes. Latterly, this fragile structure
is typically lost or collapsed during capture by nets, and
it has not been previously described or figured. Beneath the
shield is a fluid filled chamber that surrounds and protects
the eyes. Okay, so first of all, one of the
things they mentioned, there's something we've discussed regarding deep sea

creatures as well. You know, you bring these up through
the depths, stuff implodes or explodes, etc. And neurally implodes,
I guess, gets torn and what you end up with
is kind of like the deflated balloon version of the animal,
as it would exist in the depths.

Speaker 1 (32:39):
Yeah, this be like sometimes people go fishing for deep
sea fish and pull them up and it looks like
they've got some giant tongue sticking out of their mouth.
That's actually like their guts being inverted by the change
in pressure because they've got like a swim bladder, and
then when that comes up to when they come up
the pressure is too low, that inflates and it pops
their stomach out. Is really gross.

Speaker 3 (32:59):
Yeah, sometimes you'll see threads where people are like, look
at this blobfish. How disgusting? What disgusting things live in
the depths, And you almost want to see a Gary
Larson far side reversal of that situation where you have
the like luminous and deep sea creatures that are all
spread out in balloony and they have dragged like a
human body down into the crushing depths and they're like,

look at this thing, look at this disgusting creature from
the surface world.

Speaker 1 (33:25):
Yeah, or just pulled literally pull your body into the
vacuum of space and say like what a what a whimp?

Speaker 3 (33:34):
But anyway, this description they give, which I really like it,
describing it as a cowl like shield, like what they're
saying here is that there is this this clear like
shield on the top of their head. It's filled with fluid,
and inside that fluid behind that shield are its eyes.
And so this is wondrous when you start thinking about, well,

what does it mean when you have translucent or transparency
as a option for flesh on a being, you know,
imagined or otherwise. Well, like to come back to Fritz
Laber's gules, it would mean, why do you need your
eyes to be on the outside of your body at all?
Why not have more material there between your delicate eyes

and the you know, the harmful, scabby outside world.

Speaker 1 (34:22):
That's an amazing point. Yes, if you have parts of
your body that are as clear as glass, you could
put your eyes inside those parts. And yeah, yeah, I
mean in a way you could already say that's sort
of true. I mean, I guess it's not true, because
I mean, we have focusing parts that are basically right
on the exposed parts of our eyes, the cornea and
the lens and all that. But you could say that
the light sensing cells and our retina are they're not

exposed to the outside, they're in the back of the eye.
So you could just take that another step further and
just say, well, let's add another clear protective layer. Except
that's just like your skin now outside the eye.

Speaker 3 (34:58):
Yeah, with fish too, you can also I think there's
also strong argument to be made for like the various
like slimy membranes, that coat of fish as being an
extra level of protection that is generally translucent as well.
But oh and you know, just to mention the fritz
lever Ghul thing again, we also when thinking about eyes,

we also have to remember that with human eyes we
also have eye lids. Because it's not just about what
light does when it enters the eye. We also need
to control how much light is entering the eye, something
that would be I guess quite difficult if you if
your your eyelids were completely transparent. Yeah, anyway, back to

this fid, because this fish is ultimately even more amazing
because its head is kind of like a space helmet,
you know, with eyes looking out through the substance of
this call like shield. And so this leads to the
big question, why is it like this like this is
this isn't It really isn't a case of camouflage, and
it doesn't seem to be a case of like breaking

up the overall outline of the organism. So what is
the deal? So the authors here of this paper, they
write that the main hypothesis is that the shield is
there for protection. It provides protection for these eyes from
the tentacles of Nigerians, one of the apparent sources of
food for this fish. So we're talking about like stinging

jellyfishes and the like. So they're gazing up, they're hoping
to catch sight of some sort of swirling jelly mass
of deliciousness. But the thing about that swirling mass of
jelly deliciousness is that it also will have tentacles and
nematicists in there that can damage your tissue all the
better than if there's this extra layer of protection between

your delicate eyes and that all of those bioweapons. So
it's able to rise up and entangle itself in all
of that and start eating without damaging its eyes.

Speaker 1 (37:01):
So you say, this is just the raining hypothesis. I
guess this is difficult to test because this is like
a delicate deep sea organism and right access.

Speaker 3 (37:09):
Yeah, yeah, but it seems seems to be the best
argument for what's going on here, And yeah, it makes sense.
Why else have your eyes so secluded inside of this
this strange space helmet like head cranial feature. It's amazing.

Speaker 1 (37:26):
I love this fish.

Speaker 3 (37:28):
Yeah, and again these images are quite captivating. A lot
of people were amazed by this because it looking at it,
not knowing what you're looking at, it's easy to mistake
of some details on the front of the fishes, I mean,
for lack of a better word, face thinking, those are
the eyes, and it has maybe like two globular brains
or something, but that the globular things. That the things

that look like a pair of globes, those are the eyes.

Speaker 1 (37:56):

Speaker 3 (37:57):
And if you the thing is, if you look up
examples of other tubular eyed fish, you can see this
a little better. However, this fish is so popular that
if you do Google image searches for tubular eyed fish,
you're probably gonna mostly just see this guy because he's
just really taken over. He's been an Internet sensation.

Speaker 1 (38:16):
Steal in the limelight. But Macropinna is not the only
fish that incorporates transparent or translucent body elements.

Speaker 3 (38:23):
Right right, there are a number of other ones. And
now that you set it up, so I wish I
had an example of just a purely camouflaged based translucent fish.
But my next example kind of exkews the definition a
little bit, but does contain some species and specimens that
have a translucent look to them. So we're dealing with

the crocodile ice fish. These compose an entire family Chennick
the day of fish that are found in the icy
waters of the southern Ocean ant Antarctica. Now, some of
these are again small enough that photographs of specimens and
species with the right lighting do look partially translucent, but
other species and particular specimens certainly don't look crystal like.

They just look like some sort of a weird, big
headed gray fish. However, the most interesting thing about these
fish is their blood, sometimes described as white blood or
translucent blood or transparent blood. This is because their blood
is lacking hemoglobin, and they're the only known vertebrates to
lack hemoglobin in their blood as adults.

Speaker 1 (39:31):
Oh wow, interesting.

Speaker 3 (39:33):
And Joe, if you scan down in the notes here,
I included an image here from the Studiu I'm about
to site which you get to see red blooded fish blood,
and then also an example of the milky white, almost
translated I would say, translucent blood of these crocodile fish,
So it's not quite androids in the alien franchise level

of white blood. It's not like milk coming out their bodies.

Speaker 1 (40:00):
That white blood. Yeah, that was milk.

Speaker 3 (40:03):
Yeah. This reminds me of certain spirits alcohols that you'll
find that have kind of a like an opay milky
consistency without being like that white. But anyway, it's pointed
out by Sidel and O'Brien in When Bad Things Happen
to GoodFish excellent title published in Journal of Experimental Biology

in two thousand and six. This is a unique trait
due to their cold, isolated environment, resulting in not only
the loss of hemoglobin expression, but sometimes myoglobin expression as
well and to refresh. Hemoglobin is a red protein responsible
for transporting oxygen in the blood of vertebrates, and myoglobin
is a red protein containing heme, which carries and stores

oxygen in muscle cells.

Speaker 1 (40:48):
Right, So myoglobin is a great example. Like if you
ever cut open a piece of meat that you get
in the grocery store, that's probably it's got like some
red juice coming out of it. People often call that blood.
They think it is blo blood. But you know an
animal that's been butchered, has usually been drained of its
blood that's going to be myoglobin, the sort of pinkish
fluid within the muscles.

Speaker 3 (41:10):
Yeah, So without either of these being expressed and the organism,
the result is that their blood is white or colorless
or transparent, if you will. So the authors here point
out a few key details about the environment that these
fish have evolved to thrive in. So, first of all,
is really cold here, obviously, and it's not only really cold,

but it's oxygen rich. Quote, because oxygen solubility and seawater
is inversely proportional to temperature. The cold Antarctic seas thus
are an exceptionally oxygen rich aquatic habitat all. Right on
top of that, it's isolated, so you have circumpolar currents
and deep ocean trenches surrounding the continent of Antarctica, cutting

these creatures off from other fauna. And then also the
authors state that these fish need to evolve with very
little niche competition due to a mid tertiary through present
crash in fish diversity. So they've evolved yeah, yeah, so
they've evolved to do without hemoglobin because of their low
metabolic rates in this cold environment. But also due to

the high solubility of oxygen in the water at the
low temperatures in this environment. However, since their blood carries
less than ten percent of the oxygen carried in red
fish blood, they've also evolved other cardiovascular adaptations, including enormous
hearts with cardiac rates that are quote four to fivefold

greater than that of red blooded species. And so yeah,
so the authors drive home that this is blood that
works really well with creatures that live in a stable
cold water environment, and this region stabilized in such a
way roughly ten to fourteen million years ago, allowing ice
fish like this to thrive. And again, these are strange

looking fish. You look at them. Some times they do
look extremely translucent. Other times it's just kind of a
weird looking gray, big headed fish when you know there's
a big honkin heart in there working extra hard.

Speaker 1 (43:12):
Looks like a fish that would have fallen off the
garage and hit Ralphie in the eye and he ends
up crying, Yeah, broke his glasses.

Speaker 3 (43:21):
Speaking of you know, coming back to fictional accounts, I
know that the image of Micropinna, as well as images
of some of these translucent glass frogs, I think they
must have influenced the animators on the series Adventure Time,
because I can think of a few different cases where
you had some sort of a creature pop up on
that show that had some sort of translucent aspect of

its anatomy that remind me of both of these creatures.
If one does an Internet search for Adventure Time Frog Wizard,
you'll see a character named Buffo that I remember showing up.

Speaker 1 (43:57):
Yeah, okay, so wait, am I looking at the translucent
element here? Looks like it's the throat sack?

Speaker 3 (44:03):
Am I?

Speaker 1 (44:03):
Right? Yeah, kind of puffs up the sack and the
sack is translucent, right.

Speaker 3 (44:08):
Buffo has two wizard hats on his head. But yeah,
when he puffs up his throat, you see several different
little tadpoles in there that are actually the ones that speak,
and each of them has a little wizard hat as well.

Speaker 1 (44:21):
Oh wow, Oh this is also like this is a
different biological connection. The frogs that keep their they incubate
their tadpoles inside their mouths or digestive systems.

Speaker 3 (44:31):

Speaker 1 (44:32):
Yeah, I feel like for the biological trifecta here, they
should also have this wizard frog vomit up its own
stomach and scrape it out with its hands and then
swallow the stomach again.

Speaker 3 (44:43):
I got into some of this on a monster fact
a while back about I can't remember its name off hand,
but the creature from Super Mario Brothers Too that spits
eggs out of its mouth.

Speaker 1 (44:53):
Oh I remember that thing.

Speaker 3 (44:55):
Yeah yeah, But the closest comparison, drolly that I could
make between that and the natural world world, it takes
us to the realm of amphibians and frogs incubating their
eggs in curious places and in some cases ejecting them.

Speaker 1 (45:08):
This makes me feel like we got to do the
biology of why the princess can float for two seconds?
She did.

Speaker 3 (45:13):
She was good. She was my go to because she
could do that little flying thing. I would generally do her,
or I would do Luigi, but I almost never did
Mario or Toad.

Speaker 1 (45:22):
Toad. What was Toad's deal? Could he throw farther or something?

Speaker 3 (45:26):
I don't even remember. Toad was just Toad. Didn't work
for me. But then again, oh, I definitely didn't beat
that game, did not make it ver far. I got
as far as like, there's some sort of a hydras snake,
and that was that was the limit.

Speaker 1 (45:38):
There's a lot of pulling up radishes in that one.

Speaker 3 (45:42):
And pulling up of radishes and throwing a red That
was pretty satisfying, I guess, but that was way too
hard for me as a kid. I guess Birdo Burdo
was that creature's name. I had to look at Birdo Burdo.

Speaker 1 (45:55):
All right, does that do it for today?

Speaker 3 (45:57):
I believe it does. We're going to go ahead and
call it on this episode. Though, again, there are a
number of other translucent creatures we didn't have time to
get into on this episode. So if you have a
particular favorite that we didn't cover, write in about it.
We'd love to discuss it. Maybe we can break it
down in a future episode future listener mail something like that. Also,
if you have thoughts on translucent fleshed beings in various

fictional works, I'm sure it's not just Fritz Liber. There
have to be some other ones that I'm not thinking of,
or you know, the people that were influenced by by
Fritz Liber or people that influence Fritz Liber. I'm not
sure there might be some older examples to draw on,
but at any rate, we'd love to hear from you
on any and all of that. We remind you that
Stuff to Blow Your Mind is primarily a science podcast,

with our episodes coming out on Tuesdays and Thursdays. Those
are the core episodes and the Stuff to Blow your
Mind podcast feed. We usually do listener mail on Mondays.
We also do a short form artifact or monster fact
on Wednesdays, and on Fridays we do Weird House Cinema.
That's our time to set aside most serious concerns and
just talk about a strange film.

Speaker 1 (47:00):
Huge thanks as always to our excellent audio producer Seth
Nicholas Johnson. If you would like to get in touch
with us with feedback on this episode or any other,
to suggest a topic for the future, or just to
say hello, you can email us at contact at stuff
to blow your Mind dot com.

Speaker 2 (47:22):
Stuff to Blow Your Mind is production of iHeartRadio. For
more podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts,
or wherever you're listening to your favorite shows.

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