The Physics of Sea Slugs and Using Houdini

What is a Sea Slug?

A Sea Slug is an underwater invertebrate that resembles a slug. They are also a part of the gastropod and mollusk families. So essentially they are sea snails without their shells. They come in a wide variety of colors, and can be semi-translucent, bioluminescent, and gelatin in nature.

They have small razor shaped teeth, and live around coral reefs. They mostly consume plankton and algae. Most sea slugs have tentacles on the top of their heads for smelling the ocean around them, and to hunt for food. Each of these tentacles contain their own eyes. Sea slugs often have fractal-like gills and structures on their backs. These gills help them breath, and also help defend the sea slug. Nudibranchs, a type of gastropod that sheds its shell after its birth, is also considered a sea slug.

Fun Facts and Types of Sea Slugs

Sea slugs have some amazing defensive systems. They are sometimes poisonous, and are venomous to predators. But how they go about developing their poisons can be quite interesting. These techniques vary from creature to creature.

The sea slug Elysia Rufescens defends itself by eating large amounts of algae and then takes the defensive chemicals from the algae to use for its own purposes. Then when other creatures attack it, it releases the chemicals, and no longer becomes a creature’s tasty meal. However, the bacteria from this chemical is very interesting because it can generate up to 15 different chemicals from its genetic makeup. Which can be modified by the sea slug to be specific repellent to different types of fish. The bacteria is called Candidatus Endobryopsis Kahalalidefaciens, and scientists are looking into more of its properties as it could be used as a cancer treatment.

Heterobranch sea slugs are one of the most understudied marine life forms on the planet. A lot of them exist off the coast of Indonesia. Indonesia is one of the most diverse areas for sea slugs ever, and is the topic of many scientific papers.

Sea Slugs are also very weird when it comes to having “sexy times”. Unlike humans, who just want some good food and snuggles, there is a species of sea slug off of Australia’s Great Barrier Reef that likes it spiky. These Siphopteron slugs currently are unnamed , as they are a recent discovery. But the males have two penile organs on the tops of their heads, one to get the job done, and the other to plunge into its mate's eye sockets. Brains over beauty definitely has a different meaning when applied to sea slugs.

Aplysia slugs are some of the largest sea slugs on the planet. They mostly exist in tropical waters, in the Indo-Pacific Ocean, and in the Atlantic Ocean. They are herbivorous creatures, and release large clouds of black ink when threatened. Neuroscientists have conducted experiments on these slugs and found some subspecies of them have about 20,000 neurons in their brain and scattered about their body.This is very small when compared to other forms of marine life.

Kleptomaniacal sea slugs are solar powered. They steal solar cells from algae, and then use the energy from the algae when there is no food currently available. They can keep this “Solar Energy” for months on end.

Medical Research

Sea slugs are so weird that scientists use them in a lot of biomedical and behavioral research. By studying the behaviors of a sea slug, researchers hope to learn more about neuranetworks of brains, cures for diseases, and other biological processes.

For example, the sea slug Tritonia diomedea has been used in a lot of neuroethology research. Neuroethology is the study of how the brain controls behavior. By studying its navigation, feeding, mating, and egg-laying behavior they concluded that their behavior is not random, but is controlled by odors and other sensory cues. They can also sense the water currents around them, and flatten themselves out in order not to be swept away. Then the researchers started to apply these behaviors to different sensory systems in the sea slug's brain. By doing this they were able to better understand the operations of the sensory systems, central processing, and motor systems, the basic neural elements in different marine animals.

Sea slugs also play a huge part in Alzheimer's and Parkinson's research. Because sea slugs are so diverse when it comes to brain size, as well as brain cell size, it makes them great for neurology studies. Specifically studies about how memories form, and are stored in the brain.Eric Kandel of Columbia University shared the 2000 Nobel Prize in Physiology and Medicine for research on these snails regarding this topic.

However, scientists still need to discover the genes that determine the function of neurons in sea slugs. These genes can explain why we remember certain things, and why certain memories alter our behavior. Or lack thereof. Scientists have discovered that over 10,000 genes can be active within one sea slug brain cell.

But the real reason why sea slugs are so important in the study of Alzheimer's and Parkinson's diseases, is where and how these genes are shared. Scientists have found 104 counterpart genes from these diseases in sea slugs. Which concludes that sea slugs are prone to the same neurological issues we have. But how they deal with these issues still has to be determined.

Sea Slugs are also used in studies on vegitative state patients so scientists can get a better idea on how conscious victims from head trauma might be. Scientists have completed trace conditioning experiments on sea slugs, to see if consciousness can be learned, or be measured. This has had a huge impact on how doctors look for consciousness in their patients.

Visualizing The Creatures

Most of the scientific visualization surrounding sea slugs is done for creating better robots, or for engineering experiments.

For example, mathematicians have pointed to the frills of sea slugs, and their overall geometry as a resource that could help create a new generation of flexible, energy-efficient soft-bodied robots.

These frills can also be found in coral reefs, and other surrounding animals. Scientists refer to these frills as an "inflected nonsmooth surface", as it changes the direction in which it bends. Therefore, these frills are also classified as hyperbolic geometry. Hyperbolic geometry can be incredibly useful for calculating orientations, and rotations around a single point. Which many automated robots need to do if they have working joints. The joints of these robots can wear and tear over time, so finding and modeling a better joint system is always a priority. By simulating how a sea slug bends, scientists were able to figure out how a sea slug’s skeleton bends and model it accordingly for adaptation into engineering.

Sea Slugs In Houdini

In the world of sea slugs, there really haven’t been too many Houdini simulations out there. Except for one artist who from what I can gather on his instagram, is really into abstract marine systems. Nate Talbot (@nate__talbot), is a 3D visualization artist who works in a science lab in Windsor, Canada. I highly recommend checking out his instagram.

When he creates his marine renders, he works with 3D scans of plants and creatures. From there he takes inspiration from how these creatures blend into their surroundings. Then he renders them in Octane, and does the lookdev and additional simulations in Houdini.

However, if you two would like to join the sea slug train, there are a few tips, tricks, and starting points you should look into.

Sea slugs come in a variety of colors and translucency. One main thing you might want to think about is how the colors might travel over the slug, and how you are going to create those textures. You can create some interesting color patterns in VOPs, but you can also create them on the material network as well.

Uving a sea slug might be a bit difficult. As they have multiple moving parts. You might want to consider creating and simulating the slug in separate parts, so you can control everything better.

Depending on how accurate you’d like your simulation to be, you will either want to simulate your slug with vellum or FEM. FEM is more accurate than vellum, but it might take longer to set up.

Some slugs have biolumence, so you might also want to consider grouping some of its surfaces with a glow shader. Maybe animating it’s colors and brightness for extra pop.

As mentioned above, sea slugs are hyperbolic. There are a few houdini tutorials out there discussing hyperbolic geometry, so you might want to check them out if you’d like to understand their shapes more. A great one is from Junichiro Horikawa. You can check out the tutorial here: He also has an amazing tutorial on Mushroom Gills, which are very similar to sea slug gills. You can check that one out here:


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