What Exactly is: Aplysia | The Sea Hare

Added: 2026-05-30

[00:00:00]So, a little background story. You know how there are various creatures in Monster Hunter that are interesting both in design and concept. One of them is the monk snail. This giant creature is a rare endemic life that just appears sometimes and wander around the edges of the map. Because you couldn't go near it, most people probably just glance at it and move on with their life. You know, doing the actual game play. I originally played the game on Switch Light and so even though I tried to observe it with a binocular, I simply couldn't fully grasp what I was looking at. Because the Japanese name is Umeiushi Bozu, I simply thought it's an um Bozu but a sea slug. But then last week, I finally stumbled upon its model.

[00:00:46]And when I look at it, my brain immediately went, "Oh, that's just a plesia." And so I told my friend, hey, did you know that monk's snail is just aia? And she was like, what is aia? And I was like, sea hair. And she was like, what's a sea hair? And then I thought, wait, are they not a popular animal? I thought most people would know about them. Then I decided to make this video just in case it's not popular enough. So let me bring up the question. What exactly is aia?

[00:01:23]Allesia are sea slugs which means they are molest and they are gastropot. Now most people would know that there are a lot of gastropots. It's a really big class. However based on my experience many people didn't realize how vast sea slug as a group is. Sea slug is not exactly a taxonomy group. Sea slugs are whatever shellless gastropods living in the sea basically. Now, most people, or at least those who are interested in animals on a quote unquote surface level, would think sea slug is nudie branch. Oh, by the way, nudie brang should be the correct pronunciation based on its ethmology. But I'm just going to call them nudy branch because I think most people are familiar with that pronunciation.

[00:02:13]But anyway, while nudie branch are all sea slugs, sea slug is not equal to nudie branch. Various groups of sea slugs are not nudie branch, including the topic of this video. Nudie branch or nudie brank is called nudie brang because they have branchas that are nudus. Brancia is gill while nudus is naked. They are named that way because their gills are exposed. These things on their back. Other sea slugs don't have this trait. And yeah, one of those other sea slugs are the sea hairs. Sea hairs are called sea hairs because well to put it very simply, they are chunky and they look like a hair sitting on the bottom of the ocean. Oh, and while nudie branch are carniferous, sea hairs are herpiferous. So yeah, sea hair. Now the question of which taxonomic rank is equivalent to C here is debatable. The highest rank would be the order aida itself. Oh by the way this order was called aomiorpha during several periods of time but now aida is the most commonly accepted name. There are two major groups in this order. Aeridai and aidi. Those in the aerid family have external shell. And now I ask you, have you ever seen a hair with a shell?

[00:03:37]Probably not, right? And so I personally don't like to call the whole order sea hairs. Emphasis on personally, by the way. I don't mind it, not against it, but I personally prefer not to. Now to the Alesidi family. I personally think if you want an equivalent of C here in the taxonomic sense, this would be it.

[00:04:01]This is still a diverse group though.

[00:04:04]Worms listed 10 valid extent genera.

[00:04:07]Most of them have multiple species.

[00:04:09]Especially the topic of this video, Allesia. Allesia itself is a big genus.

[00:04:15]No pun intended. By the way, worms listed more than 40 valid species and even more species of dubious validities.

[00:04:23]Oh, by the way, I think they share the same ethmology as the Applicina sponge.

[00:04:29]If they do, then their name basically means unwashed, aka dirty, because, well, let's just say it's understandable why they are called that way. They can mostly be found around the tropical coast, but can also be found towards the northern Atlantic Ocean.

[00:04:47]And now, let's talk about their morphology. But before that, while they do have the same general body form, their morphology could vary because they are simply that diverse.

[00:05:04]Some of them are only around 2 to 12 cm long, like Alesia Kulifera, for example.

[00:05:10]Meanwhile, some of them are large.

[00:05:12]Allesia Vakaria, the Black Sea hair, can reach 75 cm long and weigh him more than 7 kg. I've read some articles stating it can reach 99 cm long and 14 kg of weight. But even if we stick with a 75 cm long, it is still the largest sea slug that currently exists. Largest gastropot even. I believe the second largest sea slug is the California sea hair, which is also an Allesia by the way. Allesia Californiaica or perhaps Allesia Gigantia which can be found in southwestern Australia. So yeah, like I said earlier, they are known to be chunky. Some of them have ornaments on their dorsal. Some have particular spots or maybe some patterns. Meanwhile, some look relatively simple. Like I said, the morphology could vary because they are simply that diverse. They have four sensory tentacles. two around the mouth called oral tentacles and two above the head called renoforce or you could just pronounce it rhinoforce if that's easier. Their renors give them the rabbit ear look which is debatable but yeah they also have eyes which in some species could look like camera eyes but unfortunately these are still a relatively simple oscilly and as with many other sea slugs their vision is not that good. They mostly sense their surrounding with their sensory tentacles. As with many other gastropods, they have radula and this is what they use to eat. When looking at various species in this genus, you would see these flap thingies on their dorsal.

[00:06:55]These are called parapodia. In idle state, their parapodia are folded upwards covering their back like this.

[00:07:03]And now the question is what are these things covering? And the answer is some important things actually, namely their gill and siphon. However, uncovering their parapodia also reveals their internal shell which is a relatively thin and flattened slightly convex plate. Basically there as extra protection for their mental cavity.

[00:07:26]Besides those things, there are also some glands which we'll talk about in the ecology section. Actually, let's move on to that section right now.

[00:07:37]Allesia typically resides on the fodic zone of the sea less than 200 m depth.

[00:07:42]Fodic zone is the zone where sunlight could reach the bottom of the ocean. By the way, one of the characteristics of fodic zone is the high rate of photosynthesis which means the abundance of photosynthetic organism which includes algae. And why did I specify that you might ask? Well, algae are the main diet of allesia. Different species consumes different types of algae. Some also graze on seagrasses, but yeah, like I said earlier, they are herpiferous.

[00:08:13]Most of them just crawl around on the bottom, which is a relatively slow way of moving. However, some species could swim by utilizing their parapodia, which could be faster when they need to flee from something. Quite the sight to see.

[00:08:28]More commonly though, when disturbed, they will release this ink cloud from the gland in their mantal cavity.

[00:08:35]Different species could release different color of ink cloud, but that's mostly because they consume different kinds of algae. Color is not the only thing that they got from their food, though. Some algae are also known for their toxicity and so aia could concentrate these toxins and release them together with the ink cloud. Even if it's not toxic enough for some predators, it is still unpalatable for the predators. So yeah, not only does it function as a smoke screen, it could also harm the attacker or at the very least it will deter predator, hence making it effective as a defensive maneuver. But wait, there's more. Their ink gland is not the only defensive tool they got. They also have opeline gland which secretes opeline. Opeline is the slime-like secretion and it basically functions as how a slime would function and that is it sticks to the predators making movement awkward and it disorients them. And yeah, those are the two secretions utilized by moslesia to deter predator. However, I did say most allesia. Allesia fakaria, which is the biggest of them all, does not even secrete ink. And I think they couldn't even swim. They still accumulate toxin in their body though. But yeah, the fact that they don't secrete ink is one of the reasons why you would see a lot of images of people holding them, you know, because it's safe. And also the fact that they kind of look huggable or squishable, I suppose. But anyway, another thing that we observe from Alesia is the rapid withdrawal of their gill and siphon aka GSWR which is Gil and siphon withdrawal reflex. And yeah, that is an official term. I am not making that up. In fact, there is even a dedicated Wikipedia page for that. But anyway, sea hairs are hermaphrodites. However, they still need to mate with another individual to reproduce. The smaller individual usually serves as the male while the larger individual serves as the female.

[00:10:48]They secrete protein pherommones to stimulate mating. We originally knew about attractin first. Then several years later, we discovered three other protein pherommones that react to attractin which are antistin, tempin, and seductin. And again, yeah, those are the official names. Quite something, huh? They can store and digest the sperm after they received it.

[00:11:15]And they can mate with multiple individuals. They will lay egg masses, which consists of tons of eggs in a gelatinous string. Different species could lay different colors of egg mass.

[00:11:27]By the way, I've seen some articles stating this looks like a spaghetti. And to that, I kind of want to ask this question. What kind of spaghetti have people been eating? But anyway, the embryo will develop into trophies in the egg. It will develop into at around day 10 and then the eggs will hatch at around day 10 to 15. At this stage, they are free swimming, but they will develop propodium, their food basically, and they will seek a place to settle soon. As they settle, they will continue to develop into their adult form. Allesia grow and develop quickly as they typically only live for a year.

[00:12:09]And yeah, that is aia. The things we know about them are mostly based on just a couple of species though. There are many more species that we are lacking data and observations of, so who knows what we learn in the future. But for now, let's just learn what is known. And that's all for now. Oh, by the way, Allesia is often used by neurobiologists to study neurons and electrical synapses. That is exactly why the Gillian siphon withdrawal reflex is such a specific recurring topic, by the way.

[00:12:44]Anyway, enjoy your