Saturday, 3 November 2018

Equations II: The Seager Equation

Click to enlarge; composite of web photo with painting by Gert van Dijk

The Drake equation, discussed recently on this blog, provides an estimate of how many communicating civilisations there are in our galaxy. It does so by multiplying a series of factors; none of these is rock solid, so some say it is basically guesswork. That is true, but in the absence of hard facts an educated guess is the best evidence there is. The nice thing about the Drake equation is that it in essence falsifiable, meaning that it is, at least in theory, possible to say whether there are such civilizations or not. In theory, that is, because one of the two possibilities is that are no such civilizations, and it is usually much harder to prove the absence of something than its presence. If someone in another solar system one day decides to answer our interstellar call, for instance to ask mankind to please turn the volume down, or to stop pestering them with unwanted phone calls in the middle of dinner, then we will know for certain that there is someone out there. But at present we have not received any signal, which tell us precisely nothing. It is like fishing: as long as you haven't caught any fish, you cannot conclude there aren't any. Only when you've caught one can you say that there are fish (or, more precisely, that there was at least one fish; you may just have exterminated the species).

Habitable zones (from

Sara Seager, an astronomer at MIT, proposed a different approach. If you Google her you will find many entries, among them her own website. Her reasoning rests something much more basic then intelligent being using radio signals: is there a biosphere? Her idea starts with the concept that life requires liquid water, an concept that certainly holds water (sorry for that one). Liquid water requires a planet in the habitable zone at the right distance from its star. What I learned from an overview of the conditions under which you might get liquid water is that there might even be liquid water on runaway planets that are no longer circling a star. Anyway, take a planet, add life, stir and wait, and you might get a biosphere. It is wise to search for stars with a nice quiet long term behaviour, so the stars do not cook their planets halfway down the line. Lifeforms have metabolisms, and spew out interesting gases that provide a 'biosignature' in the atmosphere around an alien planet.

Life on Earth certainly altered the atmosphere. At one point there was a nice community of anaerobic organisms quietly doing their thing, and then some new-fangled intruders called 'plants' starting using a highly polluting process called photosynthesis, with a highly reactive dangerous poison as a by-product: oxygen. Plants may have caused the very first mass extinction. Later on, animals learned to control how to burn stuff slowly with that oxygen, making a dent in the amount of oxygen, but not a large one, so Earth's atmosphere now still consists of 20% oxygen. And that can be measured from afar.

Click to enlarge; principle of spectroscopy on transit signal
Unfortunately, the detection is not easy. The method Seager proposes rests on planets passing exactly through the line of sight from Earth to the planet's star, so they appear to transit the disk of that star. That process works well and has already resulted in the discovery of many exoplanets. The TESS satellite was launched in April of 2018 to find many more. When the planets pass the star, they alter the composition of the star's light, and that change tells you something about the planetary atmosphere. Of course, not all planets happen to pass through that line of sight, so only some are observable this way. There is another problem: many biosignature gases are destroyed by ultraviolet radiation from the star, reducing their amount. These gases will be easier to detect if they are not broken down by UV, which is why Seager proposes looking at M-type stars (red dwarfs), because that live long and put out little UV. The latter job is to be done by the James Webb satellite, to be launched in 2021 (probably).    

Here is the Seager Equation:


* N is the number of planets with detectable biosignature gases
* N* is the number of stars within the sample
* FQ is the fraction of quiet stars
* FHZ is the fraction with rocky planets in the habitable zone
* FO is the fraction of observable systems
* FL is the fraction with life
* FS is the fraction with detectable spectroscopic signatures

If you study the parameters, you will see that several factors have to do with the 'detectability' of a biosphere. That holds for the fractions that concern 'quiet stars', 'observable systems' and detectable 'spectroscopic signatures'. Those fractions decrease the total number appreciably.

Click to enlarge; from:
But what is the number? Luckily, there is a very nice website allowing you to play with all the parameters in both the Drake and the Seager Equations, so you can see how they alter the final estimate. The settings shown above are for the "today's optimistic" option. Pressing calculate will give you 750 planets, while  the "Seager original values" only give you 0.45 planets. Running the Drake equation with the original settings results in 10 communicating civilizations in our galaxy. Note that the drake and Seager equations rely of completely different detection techniques, that in part explain the differences.

Does it matter for speculative biology? Well, you could say that speculative biology has to start with astronomy, so yes. In the last of these 'equation' posts, a forthcoming post on the 'Nastrazurro Equation', I will try to apply all this astronomical reasoning to speculative biology in another way. Soon. Probably.

Thursday, 1 November 2018

Furaha in ImagineFX

ImagineFX is a Bitish magazine devoted to art in science fiction, fantasy and gaming settings. Its webiste is here, and here is its YouTube channel. Most of the content is about digital painting, but they also discuss 3D applications, a bit of hardware and conventional art.

They devote several pages to work sent to them by readers, and so I decided several months ago to try my luck. I sent five images with a bit of text and waited. I wouldn't write this if the result would have been 'Thank you but no'. So, some as yet unseen images of Furaha will feature in issue 168 of Imagine FX, that will go on sale in the UK on Friday 2nd November (I think that this is the December issue, by the way). I was informed that that issue will reach the US, Canada and Australia three weeks after that date.

Click to enlarge
I haven't seen the issue yet, so I have no idea whether they will devote one or two pages to my work nor which paintings they selected. I just thought that those of you who absolutely cannot wait, and who live in the UK, might wish to know. The cover is shown above so you will know what to look for. I expect to get my own copy shortly, so I will probably write some more about it before the magazine becomes available beyond the UK.

Oh yes; a post on the 'Seager Equation' will appear this weekend, and one on the 'Nastrazzurro Equation' probably two weeks later.     

Tuesday, 9 October 2018

Back from TetZooCon

I am slowly recuperating from the TetZooCon event in London that took place on last Saturday and Sunday (that's short for 'Tetrapod Zoology Convention'). I had not been to a TetZooCon before, for the simple reason that the timing in October had always interfered with my work: October is a very popular month for all kinds of scientific conventions. But this time I had taken time off in October, and by pure coincidence TetZooCon happened to fall right in that period. I definitely will want to go to next year's TetZooCon. They're fun! I learned about whale population recovery, straight-tusked elephants, the influence of city lights on the biological clocks of birds, music in wildlife documentaries, and many, many other things. I expect that there will be a discussion of the programme on, so I will not go into details here. I will just hint at one or two things.
I was very curious about the Palaeoart workshop. The programme stated talks by Luis Rey and Mark Witton, and there was a discussion in which John Conway and Bob Nicholls also took part. In this blog I have never devoted much attention to palaeoart, although I think it can fall under the heading of 'allied matters' in the title of this blog. After all, much of palaeoart is speculative, and in that sense it is part of speculative biology. Part of the discussion was about to which extent those who like art in general would also like palaeoart. Personally I doubt that: the admittedly little I have seen of the general art world suggested surprisingly closed minds, with some Art Schools not even deigning tot teach representational art at all. Do not even mention digital painting there; that seems to lie outside that particular micro-universe altogether. The discussion also dealt with the current preference for photorealism in palaeoart. Some of the photorealistic work done by experts in that field is stunning. But I grew up with the work of people like Zdenek Burian, who worked in a much more impressionist manner. The irony here is that, whenever I aim to do something in a Burian-like style, it always turns out much more photorealistic than I wanted to.

Click to enlarge; copyright Gert van Dijk
That twist brings me to the workshop itself: John Conway asked the participants to produce palaeoart in an art style that would be new and foreign to the artist, challenging people to use materials they were otherwise unfamiliar with. I found that so much of a challenge that I missed the first 10 minutes of Luis Rey's talk altogether (sorry). In the end, I used pastels, even though I stopped touching crayons, charcoal and similar materials as soon as my school teachers allowed me to let them lie. I chose to draw a triceratops in the style used by Stone Age painters, using an Altamira bison as inspiration. The coarse effects of the pastel really fitted the subject matter well, which was more luck than intention.

On Sunday afternoon Darren Naish led a discussion about speculative biology, with Dougal Dixon and me as speakers. Dougal was his usual enthusiastic self and did very well. He had brought along a model of Greenworld (for posts on Greenworld see here and here), as well as many sketchbooks of Greenworld, that were laying on a table so everyone had ample time to browse through them during the conference. I showed a 15-slide presentation of Furaha that contained nine paintings that had not been publicly shown before, so I wondered whether people would pick up on those (so far, I haven't seen them pop up yet). Because this was just a quick introduction I did not provide much in the way of background knowledge.

Click to enlarge; copyright Gert van Dijk
Here is a slide of a subject that was published before: it is part of the banner at the top of this blog, but the one here is a reworked digital version, while the one in the banner is still the old oil painting. Hexapods form the last group I need to do to complete The Book, taking up some 10 to 12 spreads. I am thinking of giving them a thorough makeover, with important changes to their jaws and leg structures.

I showed some animations that have been shown on these blog before such as the one above, but the bigger projection scale really helps. The one above is of course a short-cloaked cloakfish. Such animations take an enormous amount of time to make, and I had stopped creating them because of that. But one of the TetZooCons talks changed my mind: Fiona Taylor spoke about the music accompanying music documentaries, and made a very strong case that music adds to the image. So I will reconsider the feasability of creating a four- or five-minute documentary about cloakfish adaptive radiation one day after all. Perhaps there will even be a professional sound track. Don't hold your breath though, as producing even one scene takes an awfully long time...

Sunday, 16 September 2018

Speculative Biology with Dougal Dixon (and me) at TetZooCon, London, 6-7 October 2018

Some of you may already know the Tetrapod Zoology blog written by Darren Naish. It has been hosted in various places over the years. It recently moved away from Scientific American to its own place, I recommend it to everyone who is interested in regular biology besides speculative biology. Actually, I suppose that everyone with an interest in speculative biology will also be interested in real biology. Darren regularly discusses speculative zoology too, by the way, so it's worth browsing through his earlier posts for that reason alone.

Click to enlarge
He also organises a yearly convention, the appropriately named 'TetZooCon'. I will simply quote from the TetZooCon pages to tell you what it is about:

Are you interested in animals, and specifically in tetrapods: that is, amphibians, reptiles, birds and mammals, living and extinct? Are you interested in their evolution, biology and diversity, in their portrayal in art, literature and fiction, in the animals of the distant past, in conservation, cryptozoology, domestication and, frankly, in just about anything relevant to the world of tetrapods? If the answer is “Hmm, I’m not sure”, you might like to go away and do something different. BUT if the answer is “Yes”, have you heard about TetZooCon? 

That should do it... This year it will be a two day event, for the first time. Although I had my eye on that convention for some time, this year is the first time that my schedule allows me to go and visit it. I already knew Darren from the World Science Fiction Convention in London, LonCon3, in 2014. Now, one thing led to another, and rather than just sit in the audience I will take part: on Sunday, October 7th, Dougal Dixon and yours truly will discuss speculative biology from 1400-1500 hrs. Afterwards there will be an opportunity for book signing by Dougal Dixon.

I hope to see you in London!

Saturday, 1 September 2018

'After Man', by Dougal Dixon; a review with hindsight

The book 'After Man' is arguably the best-known book in Speculative Biology. It first appeared in 1981, so you may well wonder why I should choose to discuss a book everyone knows already, 37 years after its publication.

Well, a shiny new edition came out. It is a facsimile edition of the 1981 version, but with some changes. I still own the copy I bought in 1981 and could easily compare the two. The new version faithfully copies the monochrome sections at the beginning and end of the book that explain basic concepts such as the nature of evolution. These, printed on a somewhat coarse type of paper, enclose the heart of the book like slices of bread in a sandwich. That heart consists of 90 pages filled with illustrations in full colour, printed in much better quality on glossy paper. Even the page numbers match up perfectly.

The few changes are interesting. The introductory text has been updated in a few places, and these are indicated with a slightly different font, a nice touch for the bibliophiles among us. For instance, the old version states that early amphibians already had 5 toes on each foot, whereas the new version says that that pattern only emerged as the standard pattern after earlier experiments with other numbers.

Click to enlarge; copyright Dougal Dixon, with permission
The middle part of the book describes animals using ecological zones as a guiding principle, but Dougal Dixon has made two changes to the illustrations. These were originally done by professional artists and were based on sketches by Dougal. That process was not always easy, as Dougal explained in an interview with Darren Naish. I own some photocopies of early sketches for Greenworld that Dougal was kind enough to send me a long time ago, so I can say with confidence that he knows what he is doing when he sketches animals. I discussed Greenword, still only available in Japanese, here, here and here. Dougal gave me permission to use the drawing above to illustrate his own skills. These are of course predatory descendants of rats (falanxes) attacking a rabbit descendant, the rabbuck. Dougal was generally happy with the illustrators' work, except for two interpretations. In the new book he replaced the drawings of the reed stilt and the night stalker with his own drawings, and they indeed look better, in particular the reed stilt, that now is a lightweight and slender creature. I will not show them here; but leave them as an incentive to buy the book.         

I could stop here and consider the job done, but I have seen some critical discussions of Dixon's works, including 'After Man'. I sometimes think these criticisms are overly harsh and would like to add a bit of background to 'After Man', meaning the time in which it appeared.

Click to enlarge; Granada Publishing 1981
Everyone is obviously free to form his or her opinion on the matter, and let me stress that I have my doubts here and there too. As an example, let me discuss the night stalker in some detail. It is a fierce predator, descended from a bat that has given up flight and is a nocturnal terrestrial hunter, using sonar to find its prey. It walks on its front legs and uses its hind legs to catch prey, for which they arch over and outside of the front legs. The image above was copied from the dust cover of the 1981 edition, showing Dougal with a model of the night stalker. Dougal is very good at making such models by the way: I saw several of them for myself on the occasion of the Loncon3 science fiction convention (discussed here by Darren Naish and here by me).

Let's follow the scenario of evolving a land-living bat with specialised grasping legs. I would not expect all those features to evolve at once, but that one would set the stage for the next. (Whales did not evolve baleens the minute they entered the water, but had to become proficient swimmers first.) I expect the first step in that process to be that the bat gives up flight and becomes an animal walking on all fours. That will force quick changes to both the front and hind legs. I would expect that freeing one pair of limbs to catch prey and using the other legs to walk on to evolve only after that. (That, by the way, would be an example of 'centaurism'; see earlier posts here and here). Which pair of legs would become grasping limbs? My guess would be the front legs, because they are closer to the prey. But if the hind legs would be used for some reason, would they reach forward on the outside of the front legs, or in between, where the entire hind part of the body might also be swung forward to extend the reach?

My second doubt concerning the night stalker is that I do not think that sonar works well for a ground-based predator, as I explained in a series of earlier posts (here, here and here). Basically, using sonar is the opposite of stealth. I would therefore expect the animal to redevelop its eyes, keeping its extraordinary hearing as a passive sense. So my personal variant of a bipedal terrestrial predatory bat descendent would walk on its hind legs and not use sonar. I think it would be fairly likely, but it would also be much more conservative and also more boring than Dougal's night stalker...  

By now you may feel that all this criticism of what is probably the most famous creation of 'After Man' is a very odd way to defend Dougal's work. But there is a point here: it is very unlikely that anyone would have been able to raise such specific and detailed considerations in 1981. Such a person would at the time have to have been a professional biologist, not a member of the general public. I am not a biologist, and I can only raise such criticisms now because of several reasons. The first is having ideas; even though I thought hard about the use of sonar for a land-living predator, someone had to have to come with that idea first, and that certainly wasn't me; it was Dougal. The second reason is that you need knowledge to think matters through; to learn, there must be something to learn from.

Suppose you find yourself in 1981 wanting to know more about some biological subject, say sonar, the evolution of whales, or any specific animal group such as 'mudskippers'. You go to a book store or ask your local librarian, who will probably come up with the same one or two books every time, leaving you both frustrated and ill-informed. Anything specific would require access to something like a university library, and even there you would on some subjects find less information than you find on Wikipedia now. There was hardly anything to fill the gap between a general interest and professional levels. The information that is readily available now with a few clicks was either non-existent or almost completely inaccessible in 1981. So what could someone interested in biology, palaeontology and science fiction find in 1981? Well, disappointingly little:

  • On the dinosaur front, you would not be happy. There were stirrings of the coming 'Dinosaur Renaissance' (Bakker's paper from Scientific American from 1975 can be found here). But Robert Bakker's book 'The Dinosaur Heresies', that spread the message that dinosaurs were lively, athletic and interesting was still five years into the future in 1981. The most spectacular book on past life that you could own at the time was probably 'Life before Man', illustrated by Zdenek Burian. It had been around at least since 1973.
  • Speculative biology did not really exist as such. An early work such as Stümpke's 'Snouters' (1957) would remain unknown to you, unless someone book dealer would decide to distribute a new printing, so you could find out about it, by chance, by browsing a book store. I found one in 1983 (under its original German title of 'Bau und Leben der Rhinogradentia'). I later wrote about them here, here and here.            
That's about it. There was no information at your fingertips. If you wished to learn something from an author, you wrote them a polite letter and hoped for the best. No internet, no Google, no computers (well, except for the Sinclair ZX-81 with a 1Kb memory). The lack of information back then would now feel like a near vacuum, and as a result even the most interested people could not possibly become as well-read as many people on the forums now are. It was in this vacuum that Dougal Dixon used his knowledge of evolution and zoology to come up with not just one odd animal, but a whole book full of them. He in fact largely defined speculative biology with 'After Man'. It was an extraordinarily creative production at the time of its first appearance, and that is the only time to judge originality and creativity. 

Saturday, 4 August 2018

Is it cruel for giants to ride mammoths in Game of Thrones?

In season 4, episode 9, of Game of thrones (GoT) there are several scenes of tame mammoths: in one, a mammoth is being ridden by a GoT giant, much as a man would ride a horse.

Click to enlarge; still from GoT; colours changed for clarity
When I saw that scene anew, my mind immediately came up, uninvited and unasked for, with the question whether a mammoth could in fact carry a giant. Is that a silly question? Of course it is, but this entire blog is to a large extent about serious answers to silly questions, so there you are.     

Unfortunately, an internet search for questions such as 'How many giants can you fit on a mammoth?'  did not provide anything useful. That was disappointing, but perhaps publishing this post will change that sad state of affairs. Forced to come up with an answer myself, I divided the problem in parts. The first asks 'What is the mass and weight of a GoT giant?', and the second concerns an educated guess at the load-carrying capacity of a mammoth.

What are the mass and weight of a GoT giant?
I had already answered that question in a post built on well-known animal scaling laws, but a later image made me think that the giants were well over twice as tall as a man, so I looked at the question again.

The basic principle is simple: if you scale an animal up with a factor x, its weight will by multiplied by the third power of x, but the cross section of its bones is only multiplied by the square of x, not enough to deal with the increased mass. Bones of large animals must be relatively thicker than of small ones. In that post, I scaled the height of a 1.8 m man weighing 80 kg up by a factor 2, but the width and breadth had to be multiplied not by 2 but by 2.8, which I rounded up to 3.0. The giant's weight became 80 x 2 x 3 x 3 = 1440 kg.

Click to enlarge; still from GoT; colours changed for clarity

In the new scene, shown above, the giant certainly seemed more than twice as high as the men around him, but foreshortening made it difficult to be certain. But if you understand perspective a bit you know that you can use vanishing points to put things into, well, perspective. The troops are standing in fairly orderly lines, allowing some lines to vanishing pints and a horizon to be drawn. Vertical lines indicate the height of the giant and a man. Once a man and the giant could be placed on the same set of lines to a vanishing point, the job is nearly done. The height of the man is given by the line AB. Using the perspective lines AB can be projected as A'B' onto the height line of the giant. All that is needed then is to estimate how much taller the giant's is than A'B'. That was about 2.8 times, so if we take a 1.75 m tall man the giant becomes an incredible 4.9 m tall. The range of 2.0 to 2.8 times a man is very large; either my estimates are off, or giants are very variable, or the makers of GoT were not too consistent with their special effects. I suspect the latter; the image at the top suggests that the giant is fairly small relative to the mammoth. Let's pretend otherwise.

Click to enlarge; copyright Gert van Dijk

Does that affect the giant's mass to a relevant degree? Yes, very much so. The graph above shows the mass of a giant for a range of scaling factors, from 1 to 2.8. Note that the scaling factor of 1 represents the original man at 80 kg. In these estimates the height of the giant is 1.75 m multiplied by the scaling factor, and the factors for width and breadth are adapted as explained before, but without rounding up (for the mathematically inclined, their factor is the height scale factor to the power of 1.5). For a giant twice the height, we get a value of 1280 kg (less than the earlier 1440 kg because I did not round up). A factor of 2.8 results in a staggering mass of 4917 kg. That is a lot of giant...

But my estimate may have been off, so let's also consider height scale factors of 2.0 and 2.4, resulting in masses of 1280 and 2654 kg. Gravity in GoT is probably the same as on Earth, as people move just as they do on Earth, so we step from mass to weight as we do on Earth (meaning without thinking about it).

Click to enlarge; left part: Gert van Dijk; right half: Mauricio Antón

I assume that GoT mammoths are the same size as Earth's woolly mammoths, because I could not find a scene that had mammoths standing conveniently still next to a group of people. Scenes of mammoths with people around them in GoT do not suggest that the mammoths were larger than elephants. I took an excellent scale drawings of extinct elephants, done by the illustrator Mauricio Anton, and put the modified giants next to them. The image was copied from this book. Mr Anton often poses animals next to another, with a background of squared giving the scale. That works very well so I copied the idea, with gratitude, and made a similar image for giants to the same scale as Antón's picture of elephants. Mind you, the left elephant is your prototypical mammth.

The giants are very, very large, aren't they? They can actually look over a mammoth. It makes you wonder whether they could in fact push them over if they wanted to...

How much weight can a mammoth carry?
The only way I could think of to answer this question was to see how much weight living elephants can carry. African elephants are not very cooperative in this regard, but there are data on Asian elephants. Apparently some people are worried that putting tourists on elephant's back harms the elephants, and I found a detailed defence by a company doing just that, saying that their elephants, with a weight range of 2081 to 5000 kg, carry tourists and gear that together make up 4.9 to 13.0% of their body weight. They also state that elephants can carry up to 25% of their weight without discomfort, but that percentage is based on studies in horses. If you look up the article on 'pack animals' in Wikipedia, you will find numbers for camels, yaks, llamas, mule, horses and reindeer. If you try to compare those with typical weights of these animals, you end up with values of about 20-30% of the animal's weight. My guess is that the percentage should be lower for larger animals, because the safety margin might be smaller, seeing how their own skeletons already make up more and more of their mass as their size increases. So it is probably wise to restrict the load on a mammoth to a maximum of 20 or perhaps 25% of their body mass.

Actually, most species of mammoth were only about as large as a modern Asian elephant, and the maximum weight of those is around 5000 kg. Several sources state that the woolly mammoth was about the size of an African elephant, so male 'woollies' must have weighed up to 6000 kg.

Putting two and two together
So we have a 6000 kg big male woolly elephant, and we make it carry 20-25% of its weight, or 1200-1500 kg. Come to think of it, it may be wise to ask the mammoth to do that rather than 'make' it do so. A discontent mammoth might cause all kinds of unpleasantness. Our giants with height scaling factors of 2.0, 2.4 and 2.8 weighed 1280, 2654 and 4917 kg respectively. Obviously, only very small giants should be allowed to ride mammoths ('small giants'??). Putting a really large giant on a mammoth would definitely constitute cruelty to mammoths. This must not be allowed to continue!

Mind you, with only one season left for GoT, and with the state of general carnage we have seen so far, all giants may by now have been recruited as soldiers in the army of the dead. Without mincing words, they are all zombified; it's sad, actually. Mammoths may all be zombified too, to the very last calf, which I personally find even sadder.

But the good news is that zombified mammoths probably are beyond suffering, so animal welfare concerns probably do not extend to dead mammoths. That's a relief!     

Saturday, 28 July 2018

Postcard from Furaha

It took longer to get back to blogging than I thought, for several reasons. As usual I had less free time than planned and a shoulder problem made painting and other computer work unpleasant. Last but certainly not least, we had such a long hot spell here in the Netherlands where I live that heat records were shattered one after the other. A few nights ago we officially had the warmest night in the Netherlands since official records started in 1854: 23.6 degrees. The temperature in my computer room reached 29 degrees... If I can't sleep, I can't write, paint, or even think properly. If the climate continues in this direction, we should stop calling ours a 'temperate' climate. Global warming anyone?

Anyway, I have worked on a painting, but extremely slowly. As I save the files often, I thought I could produce a quick post in the form of a 'making of' video. I will let the video do its own talking.
Click to enlarge; copyright Gert van Dijk
The video is small, so here is the last frame at a larger size. The painting is not finished! The potator ('Amnesialata blansjarii') still needs much work. I think I will morph it into a microrusp. Rusps do not actually have necks, but I thought it would be useful for a tree climbing animal to be able to move its head around freely. The rusp's snout will of course solve that problem to a large extent, but another way might be to recruit the first several body segements: they could become slender and lose their locomotor function, with perhaps some tiny dangling remnant limbs. I'll see. The bioluminescent stayways may reappear in the from of tetrapters. It is fun tying the various Furahan clades together, while keeping room for new developments.     
The sooner the weather normalises, the sooner I will be back with more posts.