Assorted Sea Slug Facts

So you’ve made it through the entire sea slug series. Or you stumbled upon this and now you’re very confused. Well, I ran out of general sea slug facts, but I know quite a bit about the blue dragon sea slug, so… HERE’S A POST ABOUT THE SEA SLUGS THAT I DON’T KNOW MUCH ABOUT BUT FIND COOL!!

Fun fact #1 (the one before I go off on blue dragon sea slugs): there are two sacoglossan sea slug species (alliterationnn~) that can regrow their entire body from their head. Yes, even the vital organs. This whole regeneration process takes about 3 weeks, 2 weeks less than the amount of time it takes for 5 weeks to pass. These are the Elysia atroviridis and Elysia cf. marginata sea slugs; in case you want to do more research.


THE BLUE DRAGON SEA SLUG (GLAUCUS ATLANTICUS) IS A WEIRD ONE. The little dudes float upsy-downsy on the waves, like discarded plastic. But every once in a while, a jellyfish comes by and the sea slug latches on and consumes it whole. Its favorite jellyfishy is the Portuguese Man o’ War, which is deadly to hoomans. This jellyfish is commonly known as the blue sea taco by a total of two people.

Back to the dragon slugs though. They live in ocean basins mostly, but sometimes they wash up on coasts because they suck at swimming. They’re also teeny-tiny, growing up to only one and a half inches.

Also, I forgot to add this link to the general sea slug post, so here’s a funny video talking about nudibranchs: Click this link, it’s not a rickroll. Enjoy!

Annddd that’s all for the sea slugs, and probably this year unless I get bored.

Stupidly Horrid Sea Hares

Yay. Sea hares.

To properly talk about sea hares, you first must know one thing. Sea slugs evolved from sea snails, so they lost their shells over time. Most sea slugs are actually born with shells but then move out of them in the first few stages of life. But not the sea hare. The sea hare wanted to be a slug, but it didn’t really want to not be a snail. So, it took that lovely shell and shoved it into its body.

Yeah, that’s right – sea hares have an internal shell. This shell encases their vital organs, much like a ribcage except it’s in an invertebrate. Sea hares are also very bland and large compared to other sea slugs.

The only thing saving them from me is the fact that they sometimes look a bit like tacos. They also squirt out purple ink when threatened, much like a squid. Other than that, they are boring.

Above, you’ll find a more accurate picture of a sea hare. I shall now go cleanse my brain of the sea hare by looking at pictures of sea sheep.

Sexy Sacoglossan Sea Slugs

No, I am not a sea-slug-sexual (AKA: SSS, pronounced like someone dropped a hot coal into your mouth), I just love sacoglossan sea slugs and alliteration.

Sacoglossans are part of the sea slug clade Sacoglossa and are also known as “sap-sucking slugs”. They gained this delightful title by eating a lot of algae. Most sea slugs eat plants and other sea slugs, whereas this clade’s diet consists of pretty much only algae. Through the magic of evolution, they gained the ability to steal chloroplasts from their food (this is called kleptoplasty). The way this works is quite similar to how aeolid nudibranchs use nematocysts. As the sacoglossan consumes algae, its body preserves the chloroplasts and stuffs them into its own cells.

“But won’t the chloroplasts die or something?” you may ask. And yes, the chloroplasts wouldn’t normally be able to mend themselves in a sea slug because plant cells produce specific proteins meant to heal their organelles. Through some freaky science stuff, sacoglossans have managed to prolong the lifetime of their stolen chloroplasts. This means that once they eat, they’ll be able to photosynthesize for months before needing another meal. And yes, you read that right. They fucking photosynthesize. When you wonder why scientists don’t just say plants photosynthesize and animals eat, remember it’s because of organisms like this who go out of their way to destroy all semblance of reason.

Due to their plant-like behavior, most sacoglossans have evolved to not only steal chloroplasts, but also to produce chlorophyll, leading to a green coloration. What’s more is that a number of these photosynthesizing angels look like plants or leaves.

The particular species displayed above is called a sea sheep or leaf sea slug. As you may be able to tell, they look a bit like succulents. Of course, not ALL sacoglossans photosynthesize. Only the cool ones do, the sea sheep being the ringleader of the Cool Sea Slug Gang.

Sadly, that’s all for the sacoglossans, and next time I’ll be talking about… sea hares.

Nonconforming Nudibranchs

Ah yes, the beautiful, vibrant, and deadly nudibranchs. These sea slugs belong to the clade Nudibranchia and are often divided into two sub-groups: dorid and aeolid nudibranchs. Before we get into all that, you do not pronounce nudibranch like “nudi-branch”. It’s pronounced more like “nudi-brenk” because why not.

Moving on, the first subgroup we’ll be covering is the dorid nudibranch infraorder (again, a taxonomical term). These bad boys have a branchial plume, AKA: a bunch of gills circling their anus. Yes, they do in fact breathe around their assholes, much like American politicians. Dorid nudibranchs are usually a more pastel color than aeolids because evolution. The lovely sea bunny belongs to this subgroup! That concludes the dorid segment, time to talk about the better sea slugs.

Aeolid nudibranchs are your neon sea slugs. Instead of a branchial plume, they’ve got cerata (singular is ceras). Cerata are pretty much jellyfish-like tentacles that store nematocysts. What are nematocysts? Nematocysts are stinging cells that are produced by jellyfish and a few other organisms (like hydroids). Aeolid sea slugs don’t produce these naturally, so instead, they steal them. Mature nematocysts explode on contact, but immature ones don’t, and are like buds. An aeolid’s cerata are all connected to its digestive system, allowing immature nematocysts to be carried into the tips of the cerata, into cnidosacs, where they will then mature. Gosh there’s a lot of vocabulary that needs defining. Cnidosacs are sacs at the tip of cerata that hold nematocysts and discharge them as a defense. This action is involuntary, so an aeolid can’t release its nematocysts whenever, they are only discharged as part of the organism’s fight or flight response. Aeolids also tend to have the brightest coloring out of all the sea slugs due to aposematism (their color is a warning to potential predators).

Above is the Spanish shawl sea slug, a species of aeolid nudibranch. Also, the coloring is in fact accurate, they are really that bright and colorful. The orange spine-like features are its cerata, and the orange feather-like two features are rhinophores. In this species, the oral tentacles are very pronounced.

Next up in the series is my favorite sea slug clade: sacoglossa.

Anatomy Assfoolery

So you got your sea slug, and you need to know what the fuck its anatomy even is. A very normal situation.

Above, you’ll see a diagram of a variable neon sea slug, also known as the dusky nembrotha. This is a type of dorid nudibranch, so some features may not be present in other species of sea slugs.

Let’s start from the top. Rhinophores are sea slugs’ sensory organs, and every species of sea slug has a pair; any number of rhinophores other than two is the result of a mutation (or an attack). They look soft and a bit like you took a feather-duster and hacked away at it with a pair of scissors. Next up is the oral veil. I’ll admit, there is no oral veil on the variable neon sea slug (I think), but I labelled it because a lot of species have an oral veil. This feature covers the sensitive oral tentacles and looks a bit like a hood. Oral tentacles are used to feel around and help the sea slug sense its surroundings. This is because their eyes absolutely suck. You may have noticed I didn’t label the eyes in the diagram, and that is because I couldn’t figure out where the eyes were on my reference image due to their tiny size.

Now to talk about the mantle. Not referring to the largest layer of Earth, sandwiched between the crust and core of our beloved planet. No, I’m referring to the thing in the diagram that I labelled. The mantle is most of the main body of the sea slug and is rather self-explanatory. If you’re confused, search up pictures of terrestrial sea slug mantles and you’ll get the idea. The foot is the end bit of the slug and does not house any major organs (to my knowledge). Sometimes there’s a visible transition from mantle to foot because some species have a mantle skirt, but most of the time it’s anyone’s guess.

You may have noticed that I skipped over the branchial plume. This is because it’s a feature only present in dorid nudibranchs. Thus, I’ll cover it in the nudibranch post coming up next week.

Now you know a bunch of weird buzzwords pertaining to sea slug anatomy. Go out and impress the nearest stranger with your knowledge to the point they think you’re a chronic drunk (I would say go talk to your friends, but if you’re here, I doubt you have any).


Slugs of the Seas

Alrighty. Time to talk about my passion: sea slugs.

FIRST OFF: What the fuck is a sea slug? Well, according to Wikipedia, the sea slug label applies to “some marine invertebrates with varying levels of resemblance to terrestrial slugs”. That’s a fancy way of saying it’s a slug that lives in the sea. For the sake of this, you just need to know that sea slugs are gastropods in the mollusk phylum (taxonomical term for a group smaller than a kingdom and larger than a class).

These lovely creatures can be divided into three groups, also known as clades/orders:

  • Nudibranchs: the vibrant and poisonous ones (an example being the internet-famous sea bunny)
  • Sacoglossans: the ones that look like plants and behave like plants (most of the time)
  • Sea hares: the dull (boring) ones that sometimes look like a taco

Now, because I adore sea slugs (some more than others), I’m going to make this a series! I’m definitely going to cover the different clades of sea slugs as well as their anatomy, and I might dedicate a few posts to specific species of sea slugs. Also, if this interests you, I’d suggest looking through the Sea Slug Forum; it’s a website with a bunch of posts about sea slugs, and it was made by a malacologist (someone who studies mollusks)!