Thanks to NordPass for sponsoring today's
episode. Secure your business effortlessly with a 3-month
NordPass trial by going to nordpass.com/microcosmos and using the activation code "microcosmos". If you were asked to describe
what a sea slug is, you might be tempted to go
with the straightforward response: it’s a slug that lives in the sea. And you know, you wouldn’t be wrong. You might even conjure up an image of a squirming,
squishy thing gliding through the water. But as you can see right now, sea slugs can
be spectacular, bringing together strange colors and structures that make them seem
like an adorable cartoon brought to life. At least, that’s the case for this little
guy. The true array of sea slugs is even more amazing
to behold… and also, incredibly confounding to decipher. “Sea slugs” is a very broad term, sometimes
defined as marine gastropods that don’t have a shell on the outside of their bodies. That’s because “slug” in general is
a loose term, used to describe a type of body that's undergoing the long evolutionary process
of losing a shell. Some sea slugs have lost their shells entirely,
while others are a bit more in the middle. For example, nudibranchs are a group of carnivorous
sea slugs that can have shells as larvae, but their lack of shells as an adult is a
unifying feature. This particular species that we’re looking
at belongs to the clade Sacoglossa, which does include some shelled species. But not these guys. Sacoglossans are sometimes called sap-sucking
slugs because they eat algae by sucking whatever the algal equivalent of meat is from them. And some species are famous for what they
do next. They steal from their food, taking the chloroplasts
from the plant cells and storing them in their body through a process known as kleptoplasty. We’ve seen some versions of organisms taking
on chloroplasts from others in the microcosmos, but they’ve always been single-celled organisms. And for a time, sacoglossans were the only animal we knew
of that could take chloroplasts like this. It was just a few years ago that scientists
identified a marine flatworm with the same talent. And what’s most exciting of all is that
sea slugs can actually use those chloroplasts, becoming photosynthetic animals in the process. However, the chloroplasts don’t last forever. Some sacoglossans can only maintain the photosynthetic
activity for a few days. But one species was able to hold on to their
chloroplasts for 14 months. James, our master of microscopes, came across
these sacoglossans in some samples gathered from Alicante, Spain. He’d stored the samples in a clear plastic
container and shone a strong light to help the algae in the sample. And on the second day, while he was looking
through a magnifying glass, he found one of these little creatures crawling on the surface
of the container. So he took it out with a pipette and put it
on a slide. And underneath the microscope, he found an
absolutely adorable creature, with black eyes and yellow leaf-like structures called cerata
that reminded him of a stegosaurus. At the top of their heads were a pair of rhinophores,
the antenna-like structures that help sea slugs essentially smell chemicals dissolved
in the water around them. When he checked his samples again later, he
found more sea slugs just like the first one he’d found, climbing towards the surface
where there was more oxygen. And the whole time that James spent staring
at those sea slugs, he was so excited. He’d never observed these creatures up close
before, and he kept saying to himself that this was his first nudibranch. Nudibranch? Yes, nudibranch. That other group of sea slugs that we mentioned
earlier. You know, the group that's distinct from
the Sacoglossans. We’ll cut to the chase: James was wrong. He hadn’t found nudibranchs. And there’s nothing wrong with being wrong,
especially when you’re venturing out of your well-developed comfort zone. James knows how to distinguish between countless
ciliate species based on the most minute details captured in 19th century illustrations. But these are an entirely different type of
being. But what we’ve learned in the process of
working on this episode is that sea slug people are wonderful, helpful people. When James shared his footage of these little
friends, some experts suggested that he’d found some species of Sacoglossa. And later, someone suggested that he contact
Dr. Manuel Caballer Gutierrez, a scientist at The American University of Paris whose many
research interests include marine mollusk taxonomy. Dr. Gutierrez confirmed that these were indeed
sacoglossans, and that they likely belonged to the genus Stiliger or Ercolania. But the slugs we’re watching are quite young,
which made them hard to identify. Sadly, the samples didn’t last long enough
for us to be able to continue watching them or send them to him for further identification. But after spending some more time looking
through the videos James sent, Dr. Gutierrez did narrow in on the species he thought James
had found: Ercolania viridis. We’ve found a few features that might help
with this identification, like that young Ercolania viridis tend to have
green lines close to their eyes, and that extend towards the back. The species is also known to have a white
band going down the back, though it’s not always visible. Their rhinophores are elongated and smooth,
with white spots appearing around the eyes. And there are so many other qualities to try
to draw on, from the eggs, to the shape of the cerata to their color, to their teeth. With sea slugs coming in so many different
forms, it shouldn’t be that hard to identify a species, especially when they take on such
brilliant colors and patterns and shapes, right? But there are a number of challenges. For one, adult Ercolania viridis can be quite
different in color, not just from our younger buddies here, but also from each other. Some are almost transparent, others are green,
and some are even black. That’s led to this species also being given
the name Ercolania funerea, which of course adds to the confusion. And to make things even more confusing, there
are other sea slugs with similar uses of “viridis” in their name. But sea slug researchers are a self-aware
bunch, it seems. We were looking through an old magazine called
Shells and Sea Life. On one page was an advertisement for a Nudibranchs
calendar for the year 1985. And a few pages later was an article titled “A Nomenclatural problem in the Ascoglossa— or: Why One Should Never Name a Green Sea-Slug
Viridis.” The article was written by the scientist Dr.
Kathe R. Jensen, who helpfully lays out the confounding multiple uses of “viridis”
to name sea slug species. And any clarity at all about what we’re
looking at right now is thanks to scientists like Dr. Gutierrez and Dr. Jensen, who take
the time to clarify these details not just for other scientists, but for those who might
just be curious about sea slugs. In fact, the common theme in our research
was just how many sea slug scientists have dedicated their time to crafting online resources
to help people in their journey to understand sea slugs. Their websites are formatted in ways that
are deeply familiar to anyone who spent the 2000s creating websites dedicated to the things
they loved. Perhaps the most emblematic of this is the
website seaslugforum.net. Though it’s been defunct now for more than
a decade, the forum still remains. In it, you can find helpful articles explaining
sea slugs, messages from curious sea slug finders wanting help in their identification,
and responses from people with the knowledge to aid them in their journey. The internet, for all its threat of permanence,
is also an easy place to lose information. So the preservation of the Sea Slug Forum,
even in this static state, feels like a comforting corner to recall what is good about being
able to access so many people at once, and also what's good about retaining those conversations. On this channel, we often refer to papers
that are centuries old, a form of conversation that took place between those who were curious
about a new world that had opened with a microscope. This forum is a continuation of that tradition,
but also taken to a new level. It was probably read by so many more people
at the time of publication compared to the papers of Antonie van Leeuwenhoek because
that is what our modern age has allowed us— a broader conversation, spread among so many
more people. And so today our journey through the microcosmos
may have taken us in a new direction. But like traveling around the world, these
strange sights come with parallel experiences that challenge and comfort and reveal all
at once. Thank you for coming on this journey with us as
we explore the unseen world that surrounds us. And thank you again to NordPass for sponsoring
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