Octopus Simulation Tips and Tricks

Intro

So long story short, I’ve been wanting to talk about octopuses ever since I saw @ghost3dee’s vellum work on instagram. Churro is a fascinating creation, and I’ll geek out about his work later. The second reason I’ve wanted to talk about octopuses, is that I learned that when octopuses leave sucker marks on your body they are called: Octopus hickeys….Which I find adorable.

Also maybe the octopus Ecstasy study. But more on that later.

I accept full responsibility for what this article may inspire……………* cries in Hscript.

The Biology of an Octopus

An octopus's shape is defined by its eight arms, large eyes, and bulb shaped head. Octopuses also have amazing abilities to evade predators and hide. They have three main lines of defense.

Camouflage:

Octopuses have a great ability to hide in plain sight. The pigment cells and muscles in their skin can mimik patterns in nature as well as textures.

Ink:

Octopuses, just like squids, have the ability to emit ink. This ink can block an attacker's view. This ink also contains substances that help block a predator's sense of smell.

Evasive Behavior:

Octopuses are also very fast swimmers. They can jet away from predators by suctioning away water and then expelling it. They can squeeze into small crevices, and in areas where large predators can’t follow. They can also regrow their limbs in case they are bitten off or crushed. In case of a last ditch effort to get away, octopuses can bite with their beak, and use their venomous saliva. All octopuses are venomous, but only the blue ringed octopus is deadly to humans.


Octopuses are mainly found in tropical climates. Most species can grow up to 4 feet in length, and can weigh up to 22 pounds. They mainly eat crabs, crayfish, and mollusks. Octopuses are also covered in suckers. These suction cups allow the creature to grab prey, and grab onto objects. These suckers are mainly controlled through reflex actions in the octopus’s nerves. Octopus arms will grab onto anything, because of how sensitive their suckers are. However, they will never grab their own skin.

When octopuses eat, they grab their prey and then deliver the food to their beak. However, if they are in the position where they are unable to use their limbs, they will bend around their prey, and “slurp” it into their mouths.

Octopuses are also extremely intelligent. To a point where they can recognize themselves. There are some studies that suggest that octopuses can differentiate between their own limbs and other octopuses. To a point where if they lose a limb, they will not choose to eat it, even if they are hungry.

Octopuses are considered part of the mollusk family. This makes them part of the many different invertebrates on the planet. This means they do not have the traditional bone structure that mammals do. Because they evolved in the ocean, they were not limited to any rigid structure to develop. This lack of bones helps squeeze into small places.

However, what an octopus lacks in bones, it makes up for in muscle. It’s muscle fibers help the creature keep its shape, and provide movement to its arms. It’s skin also helps it keep its shape.

There are two main suborders of octopuses. Cirrina and Incirrina. The Cirrina octopuses have semi-rigid internal shells made out of a material similar to cartilage. These structures are found in the head area of the creature, and allow for lateral fins to exist on them.

Habitat and Life Cycle

Let’s talk about where octopuses live.

As mentioned, octopuses live in tropical environments. They are selectively salt water based animals. This includes coral reefs, pelagic waters, the seabed; the intertidal zone and sometimes the abyssal depths. Octopuses don’t live long lives. Their average lifespan is 3 to 5 years. Male octopuses die as soon as they mate with a female octopus While female octopuses guard the eggs and then die as soon as the babies hatch into the ocean.

Octopuses live in every ocean. Young tropical octopuses will usually reside in shallow tide pools. However, each species has evolved differently and lives in different environments. For example, the hawaiian day octopus lives in coral reefs. While argonauts live in pelagic waters. Some species have adapted to extremely cold waters. The spoon armed octopus can be found at depths of 1,000 meters. While other types of deep sea octopuses can be found around hydrothermal vents.

Octopuses are usually antisocial, unless they are looking for a mate. (I want to make a joke about a very smart and antisocial person I know here, but I’ll hold my tongue….Congrats, I found your spirit animal.) However the pacific striped octopus has been described as fairly social. They have been seen living in groups of 40 or more. Octopuses mainly live in dens that are made up of rocky ground or other hard structures.

Octopuses have been seen dragging prey back to their dens to eat in peace and safety. Sometimes they will stock up on food inside their den and litter the remaining material around it. They will sometimes hunt with other species as well.

Octopus Studies

Octopus studies have been very popular to study from a science perspective. So let's dive into some of the many studies out there.

Recently scientists have been studying how complex brain functions work by looking at octopuses. It’s one thing to study humans, but in order to get an unbiased perspective of brain function worldwide, you need to also study animals. Because octopuses are capable of high levels of problem solving, and other cognitive behaviors, scientists are using octopuses as a model organism for this particular task.

Scientists often study animal brains. Fruit flies and zebrafish have also been a part of these studies. As they are easy to raise in a lab. However, this can limit our understanding of the experiences of these species if they are raised in a lab. For example, you’d probably have less life experience and personality if you were confined in a box all day.

But after sequencing octopus genomes in 2015, scientists realized they might have to take a look at certain species outside of a lab. When a genome of a creature is sequenced , it gives a better insight into specific genes that make the brain of a creature work. As well as how evolution helped calculate genes between species.

After sequencing the genes of an animal, scientists can then activate and create inactive cells. By don’t this they can see how neural pathways are activated in the brain of an animal, and simulate responses in a controlled environment. This also lets scientists study brain activity in real time.

Another set of brain studies that are happening are how octopuses react to different drugs. In 2018 , Dölen and co-author Eric Edsinger ( Johns Hopkins University School of Medicine) dosed a few octopuses up with MDMA and found out their neural responses changed their behavior while they were on the drug. They found that their sober octopuses would continue to be antisocial, and avoid each other. The octopuses on drugs however, acted similar to how humans experienced the drug.

The octopuses started getting frisky with each other, relaxed and became curious about what the other octopuses were doing. This sounds on the surface like a huge waste of money. Surface level, a bunch of horny octopuses floating around a lab doesn’t seem like a good idea. However, there was a purpose to this study.

MDMA (ecstasy) can be considered an empathogen. As it reduces inhibitions, social anxiety , hostility, anger, and overall fear of social interaction. So it is seen as a great drug to give to participants in controlled studies. As it can help scientists understand positive interactions between species, ease pain, and overall tension in a subject. It can also help unlock behavior that subjects might not normally display in public.

By giving octopuses this drug and watching their responses, scientists were able to conclude that these animals process serotonin the same way we do, and their serotonin transporters are the same ones that bind MDMA to vertebrates. This just means that when it comes to social behavior in animals, it could be caused less by activity in certain regions of the brain and more to do with how serotonin bonds to other molecular mechanisms in the brain.

So you’re probably wondering if it's ethical to keep octopuses in a lab setting. Or how scientists look, or raise these creatures ethically. Well, this is another reason why gene sequencing is so important. Usually , it is extremely hard to breed octopuses in a lab or a tank. So often grabbing a few from the wild and experimenting on them has happened in the past. Doing this can raise risks and stress levels for the animal. However, Marine Biological Laboratory is one place that is trying to ethically breed octopuses for science. Starting in 2016, they started to attempt gene sequencing of the Octopus chierchiae for their cephalopod breeding program. They concluded it’s small size would make it an ideal model organism to study, and unlike larger octopuses, they are able to breed them in a lab setting.

Let’s dive into the mechanics that are being created from studying octopus biology.

Starting with their skin, scientists have now been able to produce sheets with temperature sensitive dye to mimic cephalopod camouflage. They were able to create these camouflage sheets by studying how these creature’s skin works. As well as how they change color without any external input.

Cephalopod skins use a three-layered system to change color. The first layer of their skin contains a pigment in their chromatophores(organs). These organs change color in response to the signals sent out by the muscles underneath. The second layer of the skin contains light reflecting cells. These cells can turn themselves on and off within seconds. The lowest layer of cells is a layer of white cells. These cells create a bright backdrop to control the number of patterns going over the skin. However, octopus skin also contains photosensitive cells that detect light and patterns without relying on the octopus’s brain to process them first.

The scientists took this information, and then created a small multilayer grid that included temperature sensitive dye. This dye was designed to mimic the chromatophores and diodes in the octopus’s skin and muscles. Then they also added a layer of silver and light sensing diodes to mimic photosensitive cells.

The way their “skin” works is that the diodes can sense the incoming light, then they trigger the muscle-mocking diodes to heat up the dye. Then the dye turns colorless and reveals the white layer of pigment below. So their system currently can only be used for black and white color systems, but they are also working on a full color version.

Octopus vision is also a topic of interest. Octopuses don’t see in the same wavelengths as humans, so understanding how they sense other creatures and objects in their environment can help us better understand how to develop better sight technology, other tools that could be useful in science.

They also have vision that is polarized. Polarized vision is widespread in nature, and can be found in several different species. Polarization vision is the ability for creatures to see surfaces that reflect light at higher degrees than normal when their electric field comes into contact with it. You can see this “polarized effect” when you look at a highway road in the dark, or sheet plastic, glass, or water. All of these materials have a high degree of refraction.

However, every species processes these reflections and refractions differently. Thresholds for seeing polarized light can vary. Especially in Cephalopods.

Finally, Let’s talk about the arms of octopuses. They are so incredibly durable, that scientists and engineers have started to mimic them in robots.There have been several dynamic models of octopus arms out there, but let’s focus on one for today.

A team at Taishan Medical University in 2015 also created an octopus arm. This one was built to realize and mimic the large degrees of freedom an octopus’s arm has. They used coupled CPGs (Central Pattern Generators) to create the movement in the arms. CPGs are popular to use in autonomous robots because they can be programmed to complete basic tasks over and over.

They also used soft materials to strengthen the arms and made them fairly elastic. By using multiple CPGs they were able to finesse the locomotion of the arms in different areas, and simulate movement in a neuromuscular system.

Octopuses in VFX and Houdini

Ok so before we dive into 3D octopuses, let’s get this out now. We’re not gonna touch any nefarious internet octopuses. Only the quaternion vector based KineFx kind. Or whatever the
hell can explain the ungodly amount of 3Dsmax tentacle rigging tutorials out there. Let’s get started. As well as maybe a Q&A with an interesting someone later on…….

Speaking of 3Ds max, while I was writing this. A few buddies of mine shared this twitter post of an octopus built with Tyflow. Check it out here: https://twitter.com/simulationlab/status/1466544377170313220?t=DIlTnWpmcCc-F1RtbHixMQ&s=19

One of the best examples of octopuses in Houdini is Method Studios raining octopus ads. You can check out the full article on fxguide here: https://www.fxguide.com/quicktakes/raining-octopuses-how-is-this-a-thing/

In order to make these fleshy falling creatures they used Houdini’s FEM solver, while also animating them in Maya. They also created a custom “sticky” octopus rig in Houdini to get the creatures to stick to objects. They also randomized attributes to calculate how many of them would fall and hold to a given surface.

In combination with mantra rendering and practical octopus stand ins , the team was able to create something super realistic.

Thomas Marque a VFX Supervisor in France has also been displaying his octopus skills. Using Houdini he was able to develop this clever creation, as seen on instagram: https://www.instagram.com/p/Bk_9YheAcCv/?utm_source=ig_share_sheet&igshid=1saxt5w8z8qjr

After digging around on the web, I’m not entirely sure what he used in Houdini to build it, but Reddit says it was FEM, and I am leaning to agree. As he has done other experiments using FEM to make this octopus move. https://vimeo.com/270865285

There are a few different tutorials out there to teach you how to model an octopus in Houdini. However, they can be tricky to find. So here are some:

Octopus tentacle procedural modelling || VFX HOMELAND: https://www.youtube.com/watch?v=sqCcTz1Ky7o

Squid Tentacles || Tim van Helsdingen: https://www.youtube.com/watch?v=Pfc3re4lJHQ

Now let’s say you didn’t want to use FEM to create these creatures…What other methods could you use? Well you could use KineFX , Muscle systems, vellum, and custom rigs in Houdini.

With the latest updates in Houdini 19, it’s safe to say that the muscle systems are improving in the software. As well as the use of KineFX.

As it says in the documentation, these tools are still under development. So they are very “interesting” to work with. But essentially they are vellum tools and allow you to simulate muscle, tissue, and skin. As well as the rigging and animation for them. It also allows you to create natural looking muscle fibers, sliding, and wrinkles in the simulations.

Though keep in mind that the Vellum muscle system has three different simulation steps. It does a muscle, tissue , and skin pass. Between these passes you have the option to cache and save every unique pass. Lastly, it also requires you to use geometry deformers to add the muscle systems back onto your final high res mesh.

Here is a cool Vellum muscle tutorial you can check out: https://www.youtube.com/watch?v=6XBuYQadaUY

Remember, when playing with animal tissues in Houdini it is all about how you layer the simulations together. If you aren’t careful with how the muscles, skin, and tissues overlap and are constrained you might have a bit of a mess on your hands.

So here is where I thought I was almost done, but the great Matt Estela reminded me of his tentacles and so I had to give them a shoutout. https://twitter.com/thecgwiki/status/1140239037149532160

Matt was kind enough to let me dive into the tentacles so to speak, and I took a look at the file. Essentially, all the file is the piece of low res geo (the octopus), a vellum cloth simulation with distance constraints between the octopus and the torus, and a constraint to handle the tetrahedral volume of the geo. He then created a shaking movement in the tentacules using a point wrangle. Then finally simulated the movement in between the torus and the creature. Then point deformed the geo back to the original model.