Spidrids and rusps: works in progress

The main Furaha site hasn't seen any significant change for quite some time now, which makes me feel a bit irresponsible. I have devoted the time I spend on this project wholly on the blog and on new paintings. As for the site,  I will get around to a complete 'redecoration' one of these days, and the blog is what you are reading right now, so there.

I am keeping the new paintings for the book but can show you bits of works in progress now and then, both of paintings and of blog material. In this post I will show progress on two themes, not that odd as I usually work on several themes at once (a major interest at present is working out which aspects of plants can be tweaked on other worlds, and what the results would look like; that is progressing nicely).

Copyright Gert van Dijk

I have discussed spidrids here several times, the last time here. That post showed them walking on uneven terrain in a variety of gaits. Those animations, done in Matlab showed how an animal with radial symmetry changed direction without turning. Although the animations showed that well, a proper 3D animation would be better. I am not aiming to achieve the quality of Avatar or Walking with Dinosaurs, but getting to a point in that general direction would be nice. The challenge then was to translate sets of coordinates of one system (matlab) into rotation and translation values for objects in a completely different format (Vue), and then controlling Vue to make an animation one frame at a time (Python). I won't bother you with the details. As you can see above, I am now at the stage where I can control the legs and have them end up on the right orientation and position. It really looks much better at a larger size, but blogger does not allow that. The low light was chosen so I could see whether the feet end up on the correct spots of the surface: their shadows just touch them, so that works! But when the innermost segment moves beyond the vertical, that segment flips around, so my rotation subroutine isn't quite right yet. I'll solve it. Meanwhile, it's starting to look real, isn't it? Now just imagine a body in between, texture on the ground, plants and shrubs with leaves swaying in the breeze, the sound of spidrid legs on the floor, and the occasional 'chikking' of the spidrid itself. I can see it already; perhaps imagination is better than animation...

Click to enlarge; copyright Gert van Dijk

Rusps! After my last encounter with them I thought some more about a possible painting. I decided it would look good as a double page spread, occupying the top of both pages. That results in a very wide format, just the thing for an animal that is itself long and horizontal. I decided to 'stagger' successive legs: segment x has the legs placed a bit to the inside, and segment x+1 has the placed to the outside, x+2 to the inside again, etc. In that way the stride might be long without the animal knocking its legs together. As there are so many legs, each one can be skinny. So I took the 3D model of a segment I did earlier, strung them together and starting playing in Vue with positions and curves. But I also needed a head, so I sculpted one roughly in Sculptris. I do not need a detailed sculpt as the sculpt is only a simple aid to produce the painting, not an end in itself. (Then again, if I did that, I could perhaps sell you models of spidrids and rusps). That is what you see above.

Click to enlarge; copyright Gert van Dijk

Here is another view of the rusp head. You cannot see the inner design of the snout, but the story is as follows.This particular rusp species, Megacrambis brucus, is very large and has an accordingly large head. It always pays to conserve energy, so moving that massive head or even the entire body to eat one bite is wasteful. It is better to stick a small head on a long neck (sauropods) or extend the reach in another way (arms, trunks, hooks). Inside the rusps' snout, technically a  'rostrum', there are rings connected to one anther at right angles to allow pointing the rostrum in all directions. Then there is one of those intriguing linkage systems that fish in our world excel at. Putting that in action extends the reach of the rostrum two- to threefold. Finally, at the end there are some grasping mouthparts. I put some more conventional mouth parts underneath; they are probably part of the overall rusp design.

Click to enlarge; copyright Gert van Dijk

Anyway, I put all he 3D parts together in Vue and played some more, seen at the top. Below you see  a quick over painting of the result. I was aiming for an overall diagonal effect in the composition, of which the shadow falling over the rusps's body is a part. I am not certain whether I will keep it though. I will keep the strong light against the dark clouds, as it helps to highlight the front whip. Megacrambis' English name will be 'Mammoth rusp', but I am not certain yet. Furaha was first discovered by Swahili speakers, so some of their names survived. I am also considering 'Mdudu Mzee' , roughly translated as 'respected elderly bug'. Any preferences?

Predatory penguin's evolution in Brussels' future evolution back on course.

Regular readers may have noted a predilection for incomprehensible titles, or let's say titles that need a lot of knowledge to be comprehensible. This one fits that bill, I think. The previous post dealt with models of future animals in the Brussels museum of natural history. One thing that struck me was that the model of a Neopygoscelis, a penguin descendant, differed quite a bit from the earlier published design. The feet had expanded at the cost of the flippers, an evolution that I would not have expected. The designers, Marc Boulay and Jean-Sébastien Steyer, explained that the actual models had been produced without much control by themselves, explaining the changes. Marc and Sébastien are working on a book about future evolution that will appear in 2014, as told here previously (you can read starting here or here).

My discussion of the odd 'evolution' of the Neopygoscelis model persuaded them to send me two photographs of Neopygoscelis as it will appear in the book, meaning 'Furahan Biology and Allied Matters' gets another exclusive preview of that work.

Click to enlarge

The photograph above shows clearly that the model maker had evolved the enormous hind legs of the museum model quite separately from the designers' ideas. The ratio of flipper to feet size clearly shows that the flippers are still the primary propulsion method of this animal. The feet with their long nails do look formidable though, but not as a propulsion organ. The eyes are large, so the animal does not seem that large to me; the size of 4 m as stated for tye museum model seems too large for this particular animal. Note that the nails differ in size between the two animals, so I guess that we are looking at sexual dimorphism here, with one a male and one a female. I do not know which one is which, though: Marc and Sébastien sent me the photographs, but no accompanying text. That is probably wise: always leave the reader wishing for more...

Click to enlarge

The image above shows a pair of Neopygoscelis in their habitat in photorealistic mode. A very nice addition. So there are now three versions of Neopygoscelis: the digital illustration  originally shown in the magazine, the grey model in the museum that we should probably regard as a largely 'unauthorised' version, and the one in this post, that will make it into the book. That is, unless the designers feel a last-minute need to change something before the book goes to press.

I have in the past reworked oil paintings, sometimes more than once, but doing so was a big job: it involved scraping off layers of paint before adding new ones, so the process was quite destructive. Working digitally means you can do the same thing without losing anything. Most older Furaha animals were designed for visual attraction than a coherent body plan, but I am remedying that slowly, whole keeping visual appeal intact -in fact I try to improve it-. There is always a temptation to go back and push and pull at a design some more. Obviously, the same temptation works for the designers of 'Demain: les animaux du futur', but there is one big difference: there is a publisher, so there is a deadline, and so at some point the image is finished and you cannot go back any more; what a luxury.

I can't wait for the book. When it appears I will write about it here, and perhaps earlier than that as well...  

Back to future evolution in Brussels

In 2009 I wrote about a paper in a Belgian magazine showing models of future animals in the Brussels Museum of Natural Sciences. The animals later also appeared in Darren Naish' Tetrapod Zoology blog. For me, discovering the Brussels animals had as an unforeseen effect that I got to know the makers of the models, for whom designing future animals proved to be more than a single occurrence. Marc Boulay and Jean-Sébastien Steyer have been working on a book on future evolution at least since 1999. The book will be published by Belin in 2014 (in French). There are glimpses of animals as yet unseen by others on Marc's site, by the way.

Back to the future, or back to Brussels, whatever the case may be. I have now finally visited the museum; it is quite good as Natural History museums go, and specialises in dinosaurs. There is an impressive display of nine mounted specimens of Iguanodon bernissartensis, and that alone should be worth the visit. Belgium is famous for its rich supply of Iguanodons, found around 1878 in a coal mine.

Click to enlarge

As you can see, the Iguanodons are standing upright in the tripod position favoured at the time when the skeletons were mounted in 1883, not with their vertebral columns and tails horizontally as would be the case today. This is not because the museum is not up to date; it is  as far as I can tell, so I suppose they are just wary of the cost of remounting various very large dinosaur skeletons. Or perhaps there is a risk of harming the priceless skeletons, or perhaps there is an historical continuity in keeping the Iguanodons mounted according to yesterday's ideas.

The museum has a gallery of evolution, illustrating some major events and their consequences in evolution, such as the developments of eyes, of jaws, of armour and fins. There is a nice video illustrating evolutionary branching, ending for once not with man on top but with many species at the same point in time; if any species is singled out, that is -jokingly- a penguin! At the very end of that gallery there is a small group of models, and those are the animals of the future. That part of the exhibition is rather small and has not got much in the way of explanation. There is a video showing continental drift for the next 50 years, but that is about it. There are no plaques stating what is special about these animals. In fact, I saw a group of children walk by, probably ignorant of the fact that there were fundamental differences between these displays and the multitude of stuffed animals in the museum. There was a sign saying that some items had been removed from the display because of changes being made to the room's climate system; as far as I can tell a snake and a gliding mammal (Trichopteryx dixoni -surely I do not need to explain who that animal is named after-) were missing. Perhaps this also explains the lack of explanations. In this post I will add some explanations, obtained in part from the interview with Jean-Sébastien Steyer in 2009, and to a larger extent directly from his and Marc's comments on a first draft of this post.

Click to enlarge

Corticochaeris gouldi
This is a descendant of the capybara, today's largest rodent. It has become larger, with a disproportionate growth in its teeth, head and front quarters. The magazine text states it is a forest dweller, and its colours seem quite appropriate for that, mimicking spots of light falling through a leaf cover.

I had not seen the species' part of the various names before, as these are only mentioned on small plaques in the museum. The species' names reveal something about the designer's taste in biology and illustration, so they deserve mention. The name 'gouldi' is an homage to the late Stephen Jay Gould. He is considered one of the best writers popularising science of the last century, so I am glad I the designers must have felt similarly.

Click to enlarge

Propellonectes russelli
This is a one meter long descendant of the Northern Giant Petrel, Macronectes halli. As you can see it has evolved into a large flightless swimming bird, propelling itself with its feet by way of flaps on the toes that no doubt fold back with the feet are pulled forwards and that spread out when the feet move back. 

'Russelli' denotes Dale Russell, the Canadian palaeontologist who proposed that dinosaurs might have evolved into an intelligent dinosauroid.

Click to enlarge

Neopygoscelis dentatus
This is a toothed descendant of the penguin species Pygoscelis papua, so its formal name means 'toothed new brush-tailed penguin'. The teeth are apparently not just serrations of the edge of the beak, but proper teeth: the magazine interview states that birds still have the genes for teeth, and that it is not impossible for these genes to regain their expression. Neopygoscelis is an impressive four meters long. Its feet have evolved into large paddles and its wings/flippers have decreased in size, it would seem. That is odd: current penguins have very efficient flippers, so I wonder whether their continued evolution would promote feet at the cost of flippers. The animal appears not to need to climb ashore any more, which would certainly free the feet from their current restrictions as walking appendages. That would make them susceptible to evolution in another direction, but a drive towards them serving as propulsion aids has to start with a propulsion advantage right now, not a future advantage its descendants may gain from enlarged feet. Because of that, I would expect the flippers to stay in place as near-perfect propulsion limbs, and the feet would, well, what would the feet do? Turn into rudders? Disappear altogether? Turn into sexual aids? (In zoology that can always happen...)

Click to enlarge

In the magazine, Neopygoscelis was shown in a penguin-like black-and-white coat (top), but in the museum it is an overall grey colour (bottom). With the magazine in the one hand and my photographs of the museum version in the other, it became clear that the two do not represent the same model at all! Jean-Sebastièn and Marc explained that the process of having the digital designs converted into an actual model had to be done in a hurry to get the models ready for the opening of the exhibition. The result of this was that there was unfortunately not enough opportunity for interaction with the model maker, so the museum models ended up rather different from the original designs. I suppose that that explains the 'feet vs. flipper' exchange in size, which probably reflects a choice of the local model maker. 

Click to enlarge

Helicopodus buriani
For this species and the next, there is nothing in the paper and no explanation in the museum. The model confused me a lot: I could see that it has a segmented body and jointed exoskeletal legs, so it can only be an arthropod. Still, its head looked very unfamiliar, and its eyes certainly look like camera eyes, although it is hard to be certain. Again, it appears that the design suffered from a lack of time for cooperation between the designers and the sculptor. Luckily, I had help from the creators of this odd animal: what we have here is a centipede with a flattened body allowing it to glide through the air. Now that is a neat invention; of course, animals from very diverse groups developed gliding forms, including mammals, lizards, squid and insects, so why not centipedes?

It really is a pity that the museum provides so little information, not even stating that the animal is a glider! (This is a pet peeve of mine: why do museums usually only provide meagre information at infant level? With modern media it should be possible to provide information on many levels, so visitors should be able to choose the level and extent of information they want!)      

'Buriani' refers to Zdenek Burian, whom I consider to be one of the world's best painters ever of prehistoric life forms (and I am not alone in this).

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Rhombosepia gregaris
The shape and name help here: the 'communal rhomboid-shaped squid'. These are apparently  descendants of cuttlefish swimming head first instead of backwards. Drawing attention to 'swimming head first' may seem strange as it seems the normal direction; true, but squid generally swim with their tentacles trailing them, meaning that anatomically they swim backwards. In fact, many can swim either way. Swimming with the tentacles pointing the way means the tentacles have to be pressed together to form a smooth surface so as not to impede movement. As far as I remember, the thing about Rhombosepia was that its tentacles had fused. I did not check that with its inventors, but relearned that from people commenting on my own blog, who had followed links towards more information on this variant of future evolution. When I checked now, many of those links did not work any more. Those posts were only a few years old, and yet the information has been lost already. With such a quick loss of information in mind, perhaps the guardians of the Brussels museum did well in keeping their Iguanodons in their old-fashioned tripod stance. Concepts of Iguanodon stance are no older than about 125 years, but the skeletons have been underground for more than 500,000 times that length of time.

Having said that, I still find it very difficult to wait for about ONE more year for the book showing us these future animals...

Inversion fish I

In November 2012 I wrote about thomastapir's 'Xenohox Gazelle', an extremely original concept for alien animal locomotion. In that post I also mentioned that I might write about another of his inventions, the equally creative and original  'Moebius fish'.

Click to enlarge; copyright Thomastapir

The Moebius fish consists of a body sitting like a node in a complexly folded ribbon. The ribbon folds in upon itself, resulting in a complex movement. Please read Thomastapir's own descrition on his DeviantArt page, using the link above. I wish there was an animation though, as I would dearly like to see which part goes where. Luckily, the German firm Festo has produced a flying inversion device, wit a perhaps similar movement. Festo is a technology firm that often plays with biologically inspired designs, such as helium-filled balloons moving like jellyfish or manta rays. Their most recent devices include a robot flying like a dragonfly.

Festo's inversion device is shown above. This too is a helium filled balloon, shown to turn inside out in the air. It is remarkable difficult to understand what you are actually looking at. I will come back to such complex inversion shapes in a later post; the basic design consists of a series of tetrahedra (a tetrahedron is a four-sided object, with a triangle for each side). In the Festo 'inversion cube', the tetrahedra are connected to one another to form a ring. When I first saw the Festo film I immediately wondered whether that intriguing movement could be used for animal locomotion; thomastapir had already designed his Moebius fish by then though!

The whole concept of inversion shapes is interesting enough to consider how it works in a bit more detail. I will not tackle the complex shapes in this post, but will starts with the easiest version I could think of. I will call them 'fish', using that word in the time-honoured but zoologically incorrect fashion meaning 'animals regardless of descent, nature or shape, with as the only shared characteristic that they live in water'. The Festo animal is in fact a ballont, and there is no strong argument against such creatures floating in air rather then water on other planets; having them swirl around in water is so much simpler however that that is where I will put them.

The basic shape is a ring that inverts itself, so after a bit of programming here is a very simple version: a ring that continually inverts itself. I do not think that this flat shape lends itself well as a Bauplan for an animal, but give it a bit of thickness and there is room for muscles, say for starters circular muscles running lengthwise along the two rims. If one of the  two ring-shaped muscles contracts, that rim will contract and will tend to move inwards. Alternate the movement and you might get something like the 'ring fish' above.

It doubt that the animal has much to gain from the movement though: when the outer part of the ring moves downwards, that part will provide an downwards thrust, but at the same time the inner part moves upwards, providing an upwards thrust. The outer part has a larger area than the inner part, so perhaps there is a net downwards thrust, but the movement cannot be particularly effective. I wonder whether this also holds for the Festo thingy: the video is not too clear about it actually moving through the air, although it obviously moves in the air.

Let's give the 'ring fish' a bit more body. Its shape is now a torus with a triangular cross section. It is intriguing to see the movement. Again, the animal can be equipped with muscles running lengthwise around its body in the corners of the triangle. By contracting and relaxing them in the right order the fish could turn itself in and out continually as shown here. Perhaps shorter muscles running at right angles between the three ridges might help in contracting the successive ridges, to result in the inversion movement. But will it move through the water?

A natural development is to add more details, turning the torus into a smooth-skinned shape. The one above has a pentagonal cross section. The muscle arrangement would still work to make it turn inside out, but as the sides become smoother it becomes ever more clear that the inside-out movement, the 'inversion', is by itself not a sound propulsion device.

To achieve that we need a trick. Equipping the surface with something that provides traction, such as fins, would do the trick. Here, I added simple lines to the inversion fish. If the animal is microscopic the lines may stand for hairs, and at that scale hairs do provide propulsion. Lots of microscopic animals on Earth use hairs ('cilia') for that purpose. Note that the cilia do not always simply stick out from the surface, but move depending on the phase of the movement. The cilia are swung back during the upstroke so they do not provide much of a downwards force then, but they stick out during the downstroke, providing an upwards force. I assume that the animal could reverse its thrust to sim down, and if it turns on ist sde it can move horizontally. I animated just one ring of cilia, but there could easily be lots more, providing continuous force. For larger animals, change the lines into shapes with a bit of surface area, and there you are: the 'hedgehog inversion fish'.              

This design is not without its problems, unfortunately. The biggest problem is probably that it is none too obvious why they move in the way; this is rather a big problem, but I will largely ignore it -for now- . Their bodies are distorted greatly during movement: just have a look at the rectangular outlines on the body, and compare a rectangle on the inner aspect of the torus with one on the outside: to turn one into the other much stretching and squashing is needed. Some animals can do that, of course, such as octopuses, but all this distortion must limit the design severely. One way to avoid that would be to add a node to the torus that does not change shape, to house things such as a brain etc. Thomastapir's Moebius fish has such a body, and if I understand the design correctly, the body does not rotate. But if I were to equip the torus designs above with a body by just gluing it to the torus,  that body would still rotate along with the torus, so any eyes there would have to cope with a continuously rotating world view. The squashing and stretching can be solved completely by doing away with the torus and substituting a series of tetrahedra, as in the Festo device, but that is something for another post.

Five years on

On April 22, 2008 I started writing this blog without any clear thoughts on the direction it should take or how successful it should be.  I still do not know how successful it actually is, as the niche this blog occupies is so specialised. Even though I cannot compare the blog easily to other blogs, I can show you some results of the last five years.

A few days ago the count stood at 172 posts with over 225,000 page views, 1042 comments and 131 followers. This results in a mean number of page views per post of 1303. Most views last less than 15 seconds, so most viewers probably people leave the page after a quick glance, which is to be expected. Every now and again someone spends 45 or 90 minutes, though, and old posts keep on being read. I will show a number of lists to illustrate how viewers behave.

First, here are the 10 most-visited posts preceded by the number of page views:    

1. 6565 Swimming in Sand 1: the Sandworms of Dune /  Feb 2011
2. 3113 Warren Fahy's "Fragment" / Aug 2010   
3. 2814 A century of thoats / May 2012
4. 2544 Avatar's 'Walking with hexapods' or 'Don't walk this way' / Feb 2010
5. 2529 A future book on future evolution from France / Nov 2011
6. 1451 "A Venusian Bestiary", in Which Greg Broadmore Ill... / Apr 2011
7. 1408 Future evolution in Brussels / Feb 2009
8. 1353 How many legs are best for megamonsters?  / May 2011
9. 1345 Ballooning animals and Newtonian fitness / Jul 2011
10. 1312 How much more Speculative Biology is there? / Mar 2009

The list suggests that a post may become popular for three reasons: in some cases a large spike in views was generated when a large newspaper drew attention to my blog (Der Standard from Austria). Referring to popular films (Avatar), books (Fragment) or well-known names (Greg Broadmore) seems to help, and finally key words such as 'future evolution' and 'speculative biology' draw attention. Still, there are two 'biomechanical' posts with some hard science in the list. When I started doing those I wondered whether people would skip them. Apparently not; good!

Here is a list of the most often used search terms resulting in people being referred to my blog:

1. 1122 speculative biology
2. 612 future evolution
3. 566 dougal dixon greenworld
4. 262 furahan biology
5. 210 cladogram
6. 204 henders island
7. 200 planet furaha
8. 197 bobby chiu
9. 190 creature journal
10. 190 furahan

There is a definite interest for Dougal Dixon's Greenworld, so I hope it will see an English version in addition to the existing Japanese one. I was much surprised by 'cladogram'. When I use 'Google images' to find out how that word leads to my blog, a familiar cladogram appeared on the second row. Someone has copied Evan Black's Nereus cladogram from my post here to his own blog (here), with a clearly stated reference to my blog, so that is all right. I can only hope that that roundabout route also led people to Evan's own Nereus page. 

There was also some bad news: my posts were copied verbatim on someone else's blog. I am at present busy with having these posts deleted through Google, citing a breach of copyright. That seems to be working well. I will not provide links to these blogs; these people are stealing page views from my blog, so I certainly will not direct attention to them. Away with parasites!

Click to enlarge; copyright Gert van Dijk

That's enough about the blog. I have not done much with the main Furaha site, as I spent the little time I had on new digital paintings. The image above shows a study for one. I sculpted the head of an 'Ochreback Thresher' (Ira tarda) in Sculptris as a help with perspective. Its nasal horn can be used to ward off predators, but is also used in intraspecies conflicts. The horn fits under the opponent's parietal shield bosses, meaning the combatants obtain a lock on one another in which the one with the most stamina wins. The ridges on the side of the face are meant to protect the eyes (four, not well visible) from damage, but loss of one eye in dominant individuals is not uncommon. The painting will not show such a combat, by the way.

I will end with some good news and a question. I produced a 20-page sampler of The Book and have finally started sending it to publishers! I hope one will be interested, but do not dare expect much. After all, the book is as specialised as the blog, so the potential readership might be small. In my covering letter I wrote that it should appeal to people who like science fiction art and biology. If you have made it to the end of this post, you must be one of the interested people. Is that a good description of the possible readership? Is there a better one?  

Epilogue, May 2, 2013

After the post was published I noticed a surge in page views. The source was easily identified: the Austrian newspaper 'Der Standard' had published an article about the post above, in which I had drawn attention to the fact that their earlier messages had resulted in clear spikes in the number of page views concerning the posts they had drawn attention to. Confused? You may be after this epilogue, because their article not only resulted in a spike in views of the post 'Five years on' (the one you are reading now), but also in the posts already in the top ten. The top ten for the last week was:

1. 267  Swimming in Sand....
2. 239  Five years on
3. 162  A Venusian bestiary...
4. 131  Avatar, or how...
5. 91    A century of thoats    

See the list above for the links.  To close the circle of references, you may visit the article at the site of 'Der Standard'. It is entitled 'What fascinates people about fictional life forms' (but in German, obviously). You will find it here.  

Crabs as spidrids, spidrids as crabs...

I recently realised that Earth crab locomotion resembles Furahan spidrid walking more than I expected. I may have spent too much time on spidrids or not enough on crab locomotion, as there was a lot to learn about radial walking, odd as that may sound. I found a very nice paper on walking patterns of decapod crustaceans (basically crabs and lobsters) beginning with the sentence 'Most decapod crustaceans can walk in any direction they please'. 

From: Vidal-Gadea et al. Arthropod Structure & Development 2008; 37: 95–108 (adapted)

The image above is from that paper and shows leg movements of a sideways-walking crab, a forwards walking crab, and a forwards-moving lobster. The ability to move in any direction without turning the body is one of the main features of a radial walking design, something I thought did not exist on earth. Apparently crabs, particularly forwards walking ones, are quite 'radial'. In fact, the paper uses the very word 'radial' to describe leg positions for the forwards walking crab. A peculiar convergence with spidrids is that its common name is 'spider crab' (Libinia emarginata).

 Source: http://www.youtube.com/watch?v=_wZZ6N8aM3Y

While most crabs preferentially walk sideways, they can combine directions and walk diagonally if they so wish. The video above shows a crab that starts walking backwards but gradually adds a horizontal element until it ends up walking sideways only. (Click the link to see the source at a better quality).

Source: http://www.youtube.com/watch?v=uYXJ5Ww361s

And here is an example of a forward walking crab. Again, the original has better quality. If you look carefully you will see that the legs do not all point sideways: the front ones are angled to the front, and the hind ones point almost backwards. In short, they are almost placed and held radially around the body. Are spidrids crustaceoid or are crustacea spidridoid?

Click to enlarge; copyright Gert van Dijk

Spidrid legs, although the mere result of a thought exercise, are rather like real crab legs. The image above shows the simplified leg anatomy, say of a sideways-walking crab (or of a spidrid leg). The bottom part shows that the leg can turn forwards and backwards around a vertical hinge close to the body, movements labelled 'promotion' and 'remotion' in technical papers. Let's call that the 'body-leg joint'. The other joints, the 'intraleg joints', in spidrids have horizontal axes allowing the leg to be straightened and flexed (see the top part). There would be muscles for every joint, but I only showed them for one.

If the animal moves in the direction shown here the leg does not need  action of the promotor and remotor muscles: the power for movement comes from the intraleg joints.  If you rotate the direction of movement 90 degrees, muscle force for this leg has to come from the body-leg joint, meaning the promotor and remotor muscles.

Click to enlarge; Copyright Gert van Dijk

So what does all this mean for spidrids? Well, regardless of the direction it walks in, a spidrid has some legs parallel to the direction of movement and some at a right angle to it. The image above shows how that relates to the direction of movement and to the necessary range of motion. The legs parallel to the movement function as the legs in sideways-walking crabs, and  depend on intraleg flexion and extension, pulling and pushing the beastie. The legs at largely right angles to the movement depend on promotion and remotion. The leg in between simply make use of both sets of muscles to varying degrees. (Mind you, the word 'promotion' in crabs always refers towards the front end of the animal; in adapting it for spidrid use it must mean 'in the direction of movement', there being no front end.)

The next evolutionary spidrid twist stemmed from the idea that one of these two types of force production might be superior to the other. How would spidrids make use of that edge, while staying radially symmetrical? Before tackling that I realised I had never shown the spidrid's ability to change direction without turning. Solving that posed some interesting Matlab programming problems, but never mind, it works. I added height for fun and slanted the body a bit when the beastie is on a slope to make it look more natural.

 Copyright Gert van Dijk

Here it is! Finally, a spidrid that negotiates terrain and make a sharp turn. As you can see, the sharp turn calls for some interesting leg movements. With a shallow turn you would not see the changes well. So this is how real radial animals walk. By the way, should a rich Hollywood director wish to buy the concept for a film, I am available! Anyway, it is now time to adapt this standard spidrid walk to more energy-efficient gaits.

Copyright Gert van Dijk

The one above is built on the assumption that flexion/extension is more efficient than promotion/remotion. So, this species uses its promotion/remotion muscles to swing the legs as far parallel to the direction of movement as they will go. There are probably anatomical limits to this, so some legs still stick out at a right angle to the direction of movement regardless. The turn becomes odd, as some legs have to swing a long way to end up in their new position.

Copyright Gert van Dijk

But the existence of forwards-moving crabs shows that under given circumstances using promotion and remotion as the power house is feasible. The animation above has a spidrid moving its legs with a preference for positions at a right angle to the movement. This movement also calls for large leg swings when the animal changes direction. The legs bump into one another, which can be solved with phase changes, but I left it as it is for now. The anatomy of the animal is the same in all three variants, which may be unwise; I can see the last type having shorter legs to improve leverage, at the cost of stride length.

So there we are! Rampaging spidrids! What else is left for spidrid movement? An obvious additional adaptation would be to include slanting, but I will not provide an animation of that; what you see here was quite complex. Then again, I now have a program resulting in 3D coordinates for any part of a spidrid negotiating a 3D terrain. Perhaps I should go for a photorealistic animation? How about the 'Crown of Thorns' (Coruna spinea) making its way over rocks? Or the 'Blue Jester' (Fossor azureus) walking on the forest floor? The 'Lesser Strandsprab' (Nepa aranea) would do well on a beach, but the 'Hairstar' (Coma confusa) would be difficult to depict, with its hair cover. By the way, all of these appear in paintings I am working on...                    

The challenge: Tarquin's Jackjaw

So the challenge was a difficult one... Both rodlox and Petr were right: the animal indeed came from the Dr. Grordbort collection of nicely mounted Venusian insectoids. I had hoped for a proper species identification though. I guess the walls of the Virtual Main Hall will have to remain in their pristine state for the time being. Oh well.

Click to enlarge; copyright Weta Limited.

Click to enlarge; copyright Weta Limited

The animal in question is a Tarquin's Jackjaw. I found it along with four other unreleased 'Framed Venusian Wildlife Specimens' in the book "Weta, the Collector's Guide". The top image above one is a scan from the book, and the one below that was taken directly from the Weta site. The sculptor's name is not completely visible, but credit should go to where it is due: Jamie Beswarick. You can find more about him on the Weta side. 

I would rather like to own one of these display specimens, and am convincing myself that I in fact need one. Mind you, the book also contains rather large trophies of Venusian animals' heads, to hang on your wall. perhaps I will show these later, as I am rather fond of the Dr Grordbort universe.

But not next week; I will be returning to Furahan spidrids..