Friday, 8 May 2020

It's a plant! It's an animal! It's a bitroph!

Click to enlarge; Source: wikipedia

Several years ago, a species of sea slug had its day of fame on internet sites specialising in scientific news. Those sites all showed a bright green flattened blob. like the image above. This sea slug was green because it performed photosynthesis, which animals are generally not supposed to do.

I guess everyone interested in speculative biology sat up straight, because a lifeform that is part animal and part plant exudes ‘alienness’ through every pore. But was the flow of alienness coming out of those pores accompanied by oxygen, as in plants, or by carbon dioxide, something more befitting an animal? 

The slugs of the genus Elysia get their photosynthetic ability by feeding on algae. Algae, as the well-informed readers of this blog will know, perform photosynthesis in intracellular organelles called chloroplasts. The slugs eat the algae, but rather than simply digesting the chloroplasts too, they envelop then through phagocytosis, and keep them alive, in their own bodies. From then on the chloroplasts are called ‘kleptoplasts’, or ‘stolen plasts’.

It turns out that the photosynthetic slugs can live quite well in the dark, so they do not critically rely on photosynthesis. They do use photosynthesis as an auxiliary power source, mostly when they are starved anyway. When the slugs are kept in the dark AND starved, the number of kleptoplasts decreases, so the slugs then apparently disassemble the then useless chloroplasts and get a final energy boost from the hapless organelles (Cartaxana et al  2017).

Plant-animal combinations are not novel in speculative biology. Actually, there is a group of creatures  on Furaha called, for the time being, ‘mixomorphs’. They probably share characteristics with plants as well as with animals. The ‘probably’ is in there because I always had the uneasy feeling that a plant-animal combination might not work. After all, Earth is not filled with such creatures, doing whatever it is ‘plantanimals’ do when they are not just sitting in the sun. Does their absence mean that they do not make sense?

The concept of animals performing their own photosynthesis certainly sounds like a good idea. Earth plants take in carbon dioxide (CO2), water (H2O) and sunlight and turn them into carbohydrates. Because they turn nonbiological material into carbohydrates, they are called ‘autotroph’. Animals cannot do that and require some ready-made carbohydrates as a source of carbon, making them ‘heterotroph’. By breaking up those carbohydrates animals get materials for their own bodies, producing H2O, CO2 and energy. An animal is a plant in metabolic reverse, in a way.

Why not do what the slug does and cut out the middle man? This plant-animal chimaera could use photosynthesis as an auxiliary and cheap way to store free energy in carbohydrates, giving it an edge over animals that have to hunt, chew and digest to get any carbohydrates. They would even have an edge over plants in that a major problem with photosynthesis for plants is that there is so little CO2 in the air. The animal part of a chimaera would produce more then enough CO2 to boost photosynthesis of the plant part.

Click to enlarge; source: wikipedia

Autotroph + heterotroph = bitroph
There is a nice scheme on Wikipedia explaining the full nomenclature of how lifeforms get energy and carbohydrates. There are three big two-by-two divisions, shown above. These result in six fragments of phrases: hetero- vs. auto-, chemo- vs. photo-, and organo- vs. litho-. There are eight possible combinations. Our garden-variety plants (sorry for that pun...) are ‘photo-litho-auto-troph’, while ordinary animals are ‘chemo-organo-hetero-troph’.

This nice scheme seems to cover all the possibilities, creating a challenge for speculative biology lovers: where should we classify animals that can photosynthesise? Note that there already are lifeforms that cannot build their own carbohydrates and yet use photosynthesis: photo-litho- and photo-organo-heterotrophs. However, they are all bacteria, and to increase the ‘alienness’ level we want creatures we can see without a microscope, and that we can stroke, or supply with compost. Or both. Also, as these creatures would run both energy pathways, they do not fit in the scheme. They might be labelled ‘autoheterotroph’; I can't say I much like the term ‘plantanimal’. Let’s introduce ‘bitroph’ to emphasize the dual energy principle (without also adding 'photo-organo-litho-chemo-').            

Bitrophy in practice

'Bitrophism' needs consideration of energy requirements. The first question is how much energy you get from a leaf, or a standardised area performing photosynthesis.  Luckily, that information was already available on my bookshelf, in ‘Energy for animal life’ by the late R. McNeill Alexander (if you want to give your speculative biology a scientific edge, get his books). 
In bright sunlight the flux of light on the surface of the Earths is about 1000 Watt per square meter, and with that light intensity the rate of photosynthesis reaches a maximum of 21 Watt per square meter. This ratio of 21 to 1000 shows, again, how inefficient photosynthesis is. Mind you, this light flux is the maximum value in Alexander's biome, which was England. Just outside the atmosphere you get 1370 Watt per square meter. Obviously, seasons, clouds, latitude, and the time of day all influence the amount of sunlight the surface actually gets. For now, let’s go with that value of 21 Watt per square meter.

The next question is how much energy an animal actually needs. That also depends on many things, such as its activity, but it's minimum level is largely fixed: the ‘minimal metabolic rate’ describes the energy requirement of an animal doing nothing, except being alive. This rate depends on two factors.

The first is the type of animal: warm-blooded animals such as birds and mammals burn energy at much higher rates than other groups, such as lizards, fishes, etc. For two animals that have the same mass, a mammal uses almost 5 times the energy of a lizard (even one warmed up to 37 °C), and 12 times the energy of a crustacean at 20 °C.

The second factor is mass: a 100 kg animal will use more energy than a 10 kg one. However, it needs less than 10 times as much. As Alexander remarked: ”Weight for weight, it is a great deal cheaper to feed elephants than mice.”  The relationship between minimal metabolic rate (MMR) is an exponential one, and has the form

MMR = a (body mass) ^ b

(formatting is difficult here; the '^b' part means 'to the power of b'

The exponent ‘b’ differs somewhat between animal groups, but lies close to 0.75. The fact that it is less than 1 explains why large animals have a lower metabolic rate per kg than small ones. The factor ‘a’ is the one that differs between animal groups (it is 3.3. for mammals, 0.68 for warm lizards, and 027 for crustaceans.

Click to enlarge; copyright Gert van Dijk
The image above provides the Minimal Metabolic Rate the rate for mammals, (warm) lizards and crustaceans, all ranging from 0.1 to 1 kg. The crustaceans burn the least energy, and bigger animals need more energy than small ones.

But we wanted to get to photosynthesis; remember that one square meter of photosynthetic area provides 21 Watts, so I provided an additional y-axis on the right, which is simply the left y-axis divided by 21. The right one tells you how many square meters of photosynthetic area we need for each point on the graph. A 1 kg mammal will need about 0.16 square meters of ‘leaf’. That corresponds to a square with sides of 40 cm. Examples of 1 kg mammals are seven-banded armadillos, muskrat, pine martens, platypuses, meerkats and European hedgehogs. Just picture one of those them with a 40 cm by 40 cm parasol to catch sunlight. A large fruit-eating bat may also have a mass of 1 kg; it needs a large wing area anyway; hmmm...

Anyway, as I found it difficult to imagine how large that actually is, I assembled a mock animal with a mass of 1 kg (the volume can be calculated because the animal consists of spheres and cylinders; its density is 1.05). I used mammal characteristics to calculate the disc it needs to provide the energy for its MMR.

Click to enlarge; copyright Gert van Dijk

The image above shows such a 'Disneius solamor'. The small squares on the ground are 1x1 cm, and the larger ones 5x5 cm. The animal is 21 cm long, and the radius of its dark green 'sun disc' ('antenna'? 'leaf'?) is 22 cm. It needs that to power its MMR. A general human provides additional scale. Hm; the animal does not look very elegant, and that large 'leaf' looks rather vulnerable.

But we are not done yet. The calculations so far used maximum light settings, which is not realistic. And how about the effect of mass? How about animals that are thriftier with energy than mammals? How about more efficient photosynthesis? I suspect that this post may already have passed the 'maximum allowed complexity per unit of enjoyment ratio' (MACPUOER), so I will stop here. But I will very likely return to this theme.

PS. Although I welcome the large number of questions the blog has recently received, many had nothing to do with the post under which they were asked, and many could easily have been answered by using the blog's search options. So from now on I will be less likely to answer such questions.  Surely you would prefer me to spend my time working on The Book or on writing posts?

Friday, 10 April 2020

'Tabulae mortuae' (Archives XI)

Or, in English, 'dead paintings'.

The Furaha project started with oil paintings without much forethought. The reason to decide to paint something was that I thought it would look nice. Well, that obviously resulted in some designs that with hindsight simply did not make sense. As I explained in the previous post, one design involved plants with enormous leaves. That idea is gone, and so the paintings that show them are no longer useful. Let's say they lived out their lives. I will show a few in this blog. Note that they are NOT typical of current paintings; they are just stuff found in the archives.

Click to enlarge; copyright Gert van Dijk
Here is one. It really needs a better separation of foreground and background, but never mind about that. The animal in question was called a 'Mesencephalon meditans'. That name tells you it was inspired by the human brain stem (as seen from the back). Those into neuroanatomy might recognise several brainstem details, such as the 'pons'. The text regarding this animal mentioned that it might look as if it was lost in thought, but the animal would be more likely to be lost in a more general sense. That's what you get if you leave off the cortex.        

I still like the overall shape and lines of the tree. But how would it respond to wind? Would it turn around so the stem could face the wind, and the sails would flap and flutter? 

Mind you, this painting was done in oils, and for The Book it would need a digital makeover. In some cases, I used the basic idea of an old painting but changed almost everything to produce a new one. This particular dead painting was in fact resurrected. Parts of the landscape survived, and so did a much modified 'Mesencephalon'. The tree, however, did not...

Monday, 6 April 2020

Finally, Furahan plants! ('Plants VII', also 'Post #250', and 'Twelve years on')

Click to enlarge; copyright Gert van Dijk

Experience taught me that posts about plants do not attract many readers and do not generate many comments. If I wanted to maximise interest, I would probably do better to keep plants in the background and focus instead on big fierce animals with lots of teeth, or spikes, or thagomisers. But I write these posts because I like to learn (and teach, I guess).

So, this post will be about Furahan plants. For those diehards who wish to read up on the subject, see the list of posts at the end of this one. The reason to write it now is that I am working on a chapter on plants for The Book. Doing so forces me to think about the specifics of the object I am working on and to make some decisions. For instance, the wish to paint early explorers, who look at the planet Furaha from their spaceship, forced decisions about how artificial gravity and the aesthetics of interior spaceship design. Likewise, having to paint trees forced me to collapse the uncertainties about Furahan plant life into ‘facts’, although it is more like pruning fantasies: only one remains.

The very first sketches involving Farahan plants showed shapes something like the one above. (This is a quick inelegant sketch made for this post; I will show paintings of such tree designs that are now wholly defunct in a later post.) They usually had very thick trunks and had a few gigantic leaves. They were obviously alien and, I thought, visually quite appealing. But the decision to set the threshold for biomechanical aspects of Furahan life at its minimum level of ‘feasible’ dealt as much a death blow to these large leaves, as when it killed ballonts.

So Furahan plants have Earth-sized leaves, making them rather mundane. Why? Plants, as all organisms, have to find compromise between conflicting demands. If the only requirement would be to provide a place for photosynthesis, then a large thin surface would do, resulting in something resembling a bed sheet held up at a right angle to the rays of the sun. Well, that’s not what plants look like, and there must be a reason for that...

Two very important factors determining leaf size turn out to be temperature and humidity. Leaves catch light, and unfortunately that warns them up too. Even though leaves are very good at reflecting infrared light, and do not therefore warm up that easily, excess heat is still a big problem. One reason for that is that (on Earth!) photosynthesis becomes less effective at temperatures above 26 degrees. Leaf size is important for that because the air around a leaf forms a ‘boundary layer’ slowing heat exchange. This layer is bigger for large leaves, so large leaves run the risk of warming up too much. You would expect that plants in hot climes would be small, right? Maybe, but Victorian scientists had already noticed that the biggest leaves are found in the tropics, right where they shouldn’t be.

Click to enlarge; copyright as indicated; source

Leaves have tricks to cope with overheating: as the figure above shows, fake leaves in cooling experiments cooled more when they had lobed, leaflike, edges than when the edges were straight. Apparently, bits of leaf closer to an edge cool down better. Another way to stay cool is to have water evaporate from the leaves. Unfortunately, that requires lots of water, so this trick is best reserved for humid regions where water is readily available. Cooling isn’t always beneficial though: at night or in cold climes low temperatures can damage leaves, so then the ability to keep warm becomes important.

In short, leaves have overheating, freezing and water loss to contend with, all of which are affected by leaf shape and size. So how do you balance all those demands? In 2017 scientists put it all together by studying 7670 species of plants worldwide (Wright et al 2017), and finally managed to understand why big leaves are found in the tropics, right where you think they shouldn’t occur.
Click to enlarge; Wright et al 2017; source here

This figure and its legend say it all. Leaves can be big if there is lots of water to cool the leaves during daytime and also if it doesn’t get cold enough at night to harm the leaves. Basically, we are talking about tropical rain forests. That explains the circumstances under which leaves may get large, but not yet which benefit they derive from that. The authors say they think that large leaves need less twig mass, which is good because twigs do not contribute to photosynthesis. They also think that large leaves help when temperatures are marginal.

I expect that wind has an impact too, but I found surprisingly little information of the impact of wind on optimal leaf size. The reason for that lack might be that the really leaves I had in mind, from towel-sized ones, through bedsheet-sized leaves to small-sailboat-class giant leaves, do not occur on Earth. I guess that the typical tree branch anatomy, with each leaf attached by a stem to a twig that is attached to a bigger twig, etc., is a trick to absorb forces. If forces are absorbed at each level, the next level only has to carry part of a bigger load it would otherwise carry in its entirety.

Click to enlarge; Copyright Vogel et al 2009; source
Regardless of that, leaves have nice mechanical tricks to reduce the force of the wind. Some leaves take on conical shapes in a strong wind, and in other species all leaves on a twig together bundle up and reduce wind drag. The shape of the leaf even helps bring such curling about.

So where does that leave (pun intended...) those truly alien plants with giant leaves like sails? Well, nowhere. Their remaining niche would be somewhere where leaves suffer no ill effects from heating up or cooling down, or where the wind cannot harm them. The planet Furaha has wind, and its leaves do not like heating up very much. In that way they are Earth-like. So they have leaves in a form of flat thin sheets of tissue on stalks, connected to twigs, etc. It’s all rather Earth-like and boring.

But do not worry; the fact (’fact’...) that Furahan photosynthesis is more efficient than Earth’s ridiculously inefficient system ensures differences in how they look, and so does the ‘fact’ that Furahan photosynthesis responds to different portions of their star’s spectrum than Earth photosynthesis. Of course, there are the architectural differences in overall shap and trunk design too. But more on that later.

Earlier posts on alien plants
Alien Plants I
Alien Plants II
Alien Plants III
Alien Plants IV
Alien Plants V
Alien Plants VI

"Twelve years on"; Yes, I wrote the first post in this blog in 2008. This is also the 250th post I have written on Furahan Biology and Allied Matters. I intend to pick up the pace a bit from the extremely sedate rate of new posts you have enjoyed the last few years, so no big celebrations right now. Perhaps just a small applause for keeping the blog -largely- alive for twelve years?              

The main site has now moved to a new host, and some things broke while moving. They always do. I will repair them in the coming weeks. 

Saturday, 14 March 2020

Work in progress: A cloakfish documentary, with music!

Cloakfish have featured before in this blog, for instance here and here. With their four undulating fins, the 'cloaks', they lend themselves well to animation. Actually, like some other shapes and ideasm they really NEED animation. The movements of the cloaks are calculated with matlab using trigonometry, and the results is written away as a so-called obj-file and later imported in a rendering program, in my case Vue Infinite.

The animation in this post was one of my last attempts. The movements of the cloaks were calculated with Matlab, which resulted in lots of so-called obj-files that were imported in a rendering program, in my case Vue Infinite. If you look carefully you will see that the cloaks are the only moving part of the animal; that is because the rest is modelled as an unyielding and immobile blob.

The last time I showed such an animation to an international audience was at the TetZoo convention in London in October 2018, where I was given the chance to talk about the Furaha project. Afterwards I met another speaker, Fiona Taylor, who had given a talk on the use of music in nature documentaries. She showed, with examples, how strong music can influence the mood of the documentary, or in fact determine that mood. Here is Fiona's website; she has a very nice blog as well. I recommend that you read part of it, to understand the art and craft of using music for nature documentaries.

We got to talking in the corridors afterwards and she mentioned that, when she saw the cloakfish animation, she starting thinking what kind of music would fit with it. I liked that idea very much; as I have absolutely no musical talents whatsoever, the idea of getting a professional to take care of music was very appealing.

Unfortunately, I was too busy for a year to working on a big project, but that has changed now, so I have starting programming. The new programmes should result in more detail, and in particular in much more control over cloakfish form and movement. Once that is achieved, it should be easy to produce several species of cloakfish and set up scenes. After that, my computer will take over: one minute of film will require 60 times 25, or 1500, images. I would like to achieve a resolution of 1280x720 pixels, but that will depend on how long the rendering takes.

The first item on the programming agenda consisted of better mesh-producing algorithms. A 'mesh', in computer graphics, is a set of connected triangles (or other shapes) that together define a surface. Unfortunately, I cannot make use of ready-made programmes because I have no idea which programme can produce the undulating membranes that define cloakfish movement. I suppose that high-end programmes such as 3D Max and Maya can do so, but one look at their price range is enough to start looking for alternatives (doe any readers know whether Blender can do that?). One alternative, of course, is the old-fashioned hard work approach. Lacking the means to solve the problem using a lazy approach, actual work seemed the only choice left.

I chose to start on another marine animal, a 'crin', a sponge-like sessile lifeform that feeds by filtering sea water. It is simpler to produce. Crins are tube-shaped. Their plankton sieves are hidden away inside the tube. Crins can increase the volume of water they 'harvest' by pumping water actively through its tube. In some form or another they have featured in the Furaha universe from the beginning, even though I never painted one. My present aims were firstly to define it in such a way that I could produce low- and high resolution versions at will; secondly, to deform the body while keeping the mesh structure intact; thirdly, to deform the texture of the animal along with the shape itself. For the connoisseurs: that meant a better understanding of 'UV coordinates' and much better housekeeping of which vertex goes where.
Click to enlarge; copyright Gert van Dijk

This is an image of the 'Crin Designer', showing how the contour of the crin is initially defined with just a few points, shown connected with blue lines. These are connected by smooth curves, in red, that form the basis of the mesh production. The crin’s 'foot' is supposed to be fastened to a rock or something similar, but here it is just a disc. The tube does not run completely through the animal, but outward appearances are enough for now. I had not realised how much it looked like a wineglass. Perhaps I should call this species "P. grigio"...

Click to enlarge; copyright Gert van Dijk

Here is a high resolution mesh.

And here is an animation, in Matlab, of a low resolution version. The movement worked nicely, even though the water transport should perhaps be in the other direction, with water flowing in at the bottom and out through the top, instead of the other way around. In life, I imagine that crins do not pump water this energetically continuously, but only every now and then.

How about texture control? Here is a test render with a simple texture that allows me to see how the texture responds to the deformations. It worked as intended, so that's good. The deformation is simple and the background is not animated at all, but this is just a test render, after all.

And here is another test, this time with a more natural texture. It looks a bit like an octopus skin, which I like.

Work on the 'Great Cloakfish Designer' progresses nicely. But it will take quite time to get it ready, and only then can I start producing animations, even at a small size that I hope Fiona can work with. We hope to keep you informed of the progress on this blog, and possibly also on Fiona's blog.

Saturday, 18 January 2020

How well can connected boxes learn to swim? The ecosystem game

Sometimes I play a computer game, mostly of the simulation type. While looking for something different from steering a European nation through history, or building a sprawling city somewhere, I came across a game promising to show biological evolution.

It would not be the first time a game tried to do that; Spore promised that too, and there are some others. I even wrote a post about Spore for this blog, because I was curious how the game designers dealt with the number of legs a creature might have. That number did not evolve by itself, but was chosen by the player. While the anatomy and movement of these legs were cleverly arranged, they turned out to be completely predetermined. In other words, the gradual changes in shape and capabilities of the resulting beasties had nothing to do with random variability followed by the environment pruning the stragglers, which is how real biological evolution works. Instead, Spore relied on Intelligent Design by the developers, and to a lesser extent by the player, acting as a minor deity.  

Click to enlarge; copyright Tom Johnson
But this ecosystem game promises the opposite. You get to play with a barren stretch of sea floor and have to turn it into a thriving ecosystem. The game will create swimming animals completely on its own, at first anyway. There is random genetic variability, and the unfit are weeded out, leaving their more successful brethren to forge on. You may wonder whether a full evolution simulation handled in this way would be any fun to play. After all, the premise would firstly be that genetic, anatomic and functional variability are all left to chance, and secondly that the environment provides all the selection pressures. What is left for the player to do?

In the demo, the player can indeed not control the characteristics of the beasts at all, but can guide evolution by altering the environment. The player has to place new plants or simple animals as food, and will also have to provide spawning areas and cordon off some pleasant mating grounds. Then you watch to see whether your Chosen Species rises to your challenge.

In the final game, there will also be a possibility to tinker with the anatomy of the beasts directly. An example of how that may look is shown above. Much as I like the idea of a fully independent evolution model, I also look forward to take up my duties as Minor Deity and start tinkering. In the full game you do not need content yourself with one Chosen Species; there will be various species, and herbivores as well as predators. At present, the game is in an early stage, so do not think you can lord it over a complex ecosystem just yet. That will be later. But a large part of the true evolutionary part is already in place. Let’s discuss the mechanics and the nervous systems of these beasts.

Tom Johnson, the creator of the game, provided some explanations. The animals consist of connected rectangular boxes of varying width, length and breadth. That’s it: they are boxes. That is what is shown in the video above. In the game, the animals look much nicer, as the boxes are depicted as smoothed forms with some nice fishy textures. At one end of one box there is supposed to be a mouth. To help the player, this part is shown as having a distinctively fishy head, with two eyes and two jaws. In a way this is a pity, as otherwise the animals have nothing that reminds you of a vertebrate. They are wholly and spectacularly asymmetrical! The boxes move at the connecting points, sometimes around one axis, sometimes around more than one. If one box moves with respect to another, this creates forces acting on the water around our hopeful monster. There is drag, there is angular momentum, and the creatures moves. Well, if you play the demo you will find that the earliest forms flop rather than swim and can be so painfully clumsy that they die before they even make it to any food.

The animals have nervous systems with an input layer, a layer for connection and integrationr (the Brain!) and a layer of output neurons controlling the muscles of each body part, which is, unsurprisingly, a box. You can actually see the neuronal connections in action, with impulses speeding along the axons (although at present the number of visible impulses does not reflect the true impulse frequency yet – for that you have to look at the number next to the neuron-). In successive generations, both the anatomy of the boxes and their nervous systems evolve. It is not quite clear to me yet whether the neural system develops at random or in response to mechanical needs. At any rate, I think it is an impressive feat to have both an evolving anatomy as well as an evolving brain linked to that anatomy.

Tom told me that the capacity of the evolutionary fitness principle was well born out by the game. At one point it turned out that some features of the animal worked only with a specific frame rate. In other words, the modelled animals had taken full advantage of one characteristic of their particular world, even though that was a completely unintentional one.

Another example is the animation above this paragraph: the animal seems to wave one limb in such a way that it acts as sort of propeller. In my searches for original means of locomotion to use on Furaha, I had tried to find a way to have a limb do just that. The problem is of course that in biology you cannot have a body part going through a complete 360 degree turn, as that would of be incompatible with blood vessels, nerves and muscles running to that limb. I could not see well enough how the movement worked, so I asked Tom. His reply was that I needn’t bother, as that was an early design, and he had not specifically stopped the animals from having continuous circular motions. So, again, blind evolution had used what it could and found a way...

Tom was kind enough to send me a unique illustration for this blog, shown above. The wrote: "This creature lives in the deep sea with a rocky, spiked terrain and evolved a nice downward glide to stick to the seafloor and eat the sessile creatures attached to it." I like it.

As I said, at present this game is available as a free demo, here or here. I will be keeping my eye on it, to see what strange forms can and will evolve. Charles Darwin once wrote the following about evolution:

 “There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.”

Isn’t it fascinating that we can now see these principles in action, right before our eyes, on our computer screens?

Wednesday, 13 November 2019

Work in progress: the prigoon again

Lately, I have been wondering whether it is really a good idea to keep the paintings hidden until the publication of the eventual book. If I do not show the paintings, then I should probably keep interest going by writing posts more often. But the kind of posts I write, with literature searches and illustrations made to order, take a lot of time.

Perhaps I should write some shorter posts instead, just short ones, without much depth. Let me known what you think of such an approach.

Click to enlarge; copyright Gert van Dijk
 To try it out, here is a work in progress: I have worked on the prigoon's head and back shield. I like painting textures, and thought I should try my hand at iridescence.  The legs need to be detailed, but that is fairly boring work. After that I wil work on the shdows some more, because the animal is a bit flat right now. At the very end I will probably use blurring to create the idea of macro photography.

Monday, 21 October 2019

The prigoon: a secondary bilateral spidrid

I cannot imagine that anyone will remember that I wrote about animals that walk on five legs in this blog. Actually, I hardly did, and that is not surprising as it was almost exactly 10 years ago. Well, I did remember that I wrote about 'odd walkers', but had forgotten that I had actually produced an animation for an animal with two pairs of legs and an unpaired one.

So why bring this up? Because I am working on a painting of a 'secondary lateralised spidrid'. It's a small exoskeletal predator. Think of a jumping spider on Earth. The animal is descended from radially symmetrical spidrids, and during its evolution the new plane of symmetry somehow came to run through two opposite pairs, rather than between them. Mind you, these exist too, but for unknown reasons the latter group is almost exclusively herbivorous, while the ones with one jumping leg are mostly predators.

Click to enlarge; copyright Gert van Dijk
So here is a colour sketch. I think I will call it a 'prigoon', but I haven't thought of its binomen yet. The name will probably contain 'dougalii'  or 'dixoni', as Dougal Dixon was the first to come up with this odd arrangement, and I wouldn't want people to think I am quoting anything without a proper reference.