A psychotherapist space spider

The recent Netflix film 'Spaceman' is an adaptation of the book Spaceman of Bohemia, written by the Czech/American author Jaroslav Kalfař. It is about a lone Czech astronaut travelling a long distance in the solar system to investigate a strange space cloud. A major theme of Spaceman is the loneliness of the astronaut. If you like philosophical themes and are not in a hurry, Spaceman is well worth watching; however, those who prefer ray guns and explosions might like it less.

But this blog is about speculative biology of the extraterrestrial kind, not about film reviews. While the astronaut, Jakub Procházka, is lonely and far away from other people, he is not alone. I am not talking about the ship's cat here, not that seems to be one. An alien being that is best described as a spider the size of a small child shows up aboard. How is unclear and you will probably wonder whether the spider is real or whether we see a hallucination springing from Jakub's too lonely mind. The internet seems full of discussions of that particular topic, so I will not discuss this. Well, in fact, you do see a small spider moving under Jakub's skin in the beginning of the film, which seemed to me a strong hint that the spider originated inside Jakub, not as a physical being, but as a concept.    

Anyway, the nice thing is that we get to see the space spider in sufficient detail to analyse it as a speculative biology entity. 

Why is it called a spider? You wouldn't expect alien beings to conform to Earth cladistics, after all. But there are certainly similarities. It has eight legs with long slender elements sticking out sideways. There is a big bulging abdomen, as well as a head. If it would be a proper Earth spider, that head should be fused with the trunk to form a cephalothorax, but this space spider head seems movable relative to the trunk part. The head has six eyes, not eight, even if some reviews mention eight. 

Click to enlarge. Nentwig et al. All you need to know about spiders. Springer 2022 

 

Click to enlarge. Nentwig et al. All you need to know about spiders. Springer 2022 

The eyes of Earth spiders are quite interesting and variable between families of spiders. There are not always eight, in fact, and six is definitely possible with Earth spiders. The two images above show that clearly. The eyes of our space spider, christened Zanuš by Jakub, appear to have pupils. The eyes seem immobile, and they are enclosed by a ring of elastic tissue, allowing them to become larger and smaller in apparent diameter. That is a clever trick that helps convey emotions. There are two large eyes and four smaller ones, but otherwise they all look the same. On Earth, different  eyes have different functions, and that shows up in their size, colour as well as the apparent direction they seem to be aimed in. We will get back to that later.

There are two very large cheliceres pointing straight down from underneath the head. I haven't seen Zanuš using these fangs and do not know what they are for. Then again, what can fangs be for? It does make you wonder what these space spiders do in their natural environment.

There are additional limbs around the mouth, and in one touching scene, shown above, Zanuš accepts a spoon from the astronaut with some food on it. These mouth limbs can then be seen to be tentacles, and tentacles are definitely not in the anatomical repertoire of Earth spiders.

There is one more big departure from the Bauplan of Earth spiders: Zanuš is obviously endoskeletal, as can be seen from the clip. There are tendons connected to bones, and the entirety of the body is covered by hairy skin. This is certainly not an exoskeletal joint with hinges open to the outside world. The joints are, like vertebrate joints, well and truly inside the leg. The legs, by the way, end in two prehensile fingers each. Zanuš clambers around the inside of the spaceship grasping objects with these tiny hands.

So what does all this suggest? A first explanation is that, if Zanuš is a figment of Jakub's imagination, Jakub knows very little about spiders. I doubt that real astronauts get much zoological training, so that is fine. A second option holds that Zanuš is a real being; inside the story, of course. If so, his Bauplan is interesting, and we will get to that. The third level is the one the creature designer and film makers used: why did they choose this design? 

Let's play along and see what we can make out. We have an endoskeletal animal the mass of a small child, with lots of fairly thin legs sticking out sideways. The legs, fur and locomotion all suggest a terrestrial origin; this is not a swimming animal. The legs are very spindly and stick out sideways; that, plus the presence of tentacles, suggests a world with very low gravity. The ability to grasp objects all around further suggests that the creature would be at home in a 3D environment, such as tree branches. 

Click to enlarge. Nentwig et al. All you need to know about spiders. Springer 2022 

One thing bothers me in all this: Zanuš' eyes all look in the same direction. In a 3D environment, it pays to be able to look in most directions at all times. If your Bauplan has multiple eyes, it makes sense to move some to achieve all-around vision. Spider eyes follow that principle, at least for some families, as shown above. In contrast, if your Bauplan only provides two eyes, which is a poor choice if you ask me, then evolution can be expected to place them where they do best. Here, they would be seeing what you eat and also covering as much of the world as possible. Not surprisingly,  the eyes of many fishes and birds that do live in a 3D environment are placed at just the right spot to achieve such goals. Of course, many birds and mammals have eyes that  depart from that pattern. If you only have two eyes, stereoscopic vision can apparently outweigh the need for wraparound vision. With multiple eyes, you can easily get it all, but Zanuš' eyes all look ahead. That seems odd.

In the story, Zanuš proves to be a thoughtful and respectful psychotherapist. You need good eyes to pick up tiny nuances in expression, posture and movements that tell you a great deal about someone's state of mind, but not eight ones!

A final word in this rather meandering post. I cannot speak for the general audience, but I quickly liked Zanuš, perhaps because I am not really afraid of bugs and small arthropods. I rather like it that the film makers dared choose a shape that many people find repulsive. I do not know whether many people actually turned the film off, disgusted by Zanuš' spider shape. I hope not, because the world could do with a bunch of sympathetic Czech/alien psychotherapist space spiders. Then again, I still wonder what Zanuš' people use those enormous fangs for on their home world...

Walking on Kepler-22b, or: How many legs are best for megamonsters? II

The documentaries 'Alien planets revealed' and 'Aliens: are we alone?' are nearly identical productions about the Kepler satellite, looking for planets around other stars. Planet hunting has been very successful: in a few years knowledge expanded from not knowing whether our own solar systems was the only one in existence  to the realisation that planets are a dime a dozen. The free app 'exoplanet' regularly updates what is known about such planets. At the time of writing it has data on 1768 confirmed exoplanets. Most are 'hot Jupiters', massive planets very close to their stars. They, and any moons orbiting them, are too hot for Earth-like life, so what everyone is really looking for are planets of an Earth-like mass circling their star in its habitable zone. This 'Goldilocks zone' is not too hot, nor too cold, but just right to have water in fluid form and therefore life as we know it.

From Exoplanet app; click to enlarge

The various techniques of detecting exoplanets all have in common that the planets most easily detected are the most massive ones close in to their star. Even so, techniques gradually get better and smaller and smaller planets can be detected. The graph above was produced by the exoplanet app, and shows the mass of planets compared to the year of discovery: if techniques keep on getting better, many planets with a mass around that of Earth will be discovered in the near future, and we may even expect much smaller planets to be discivered. I suppose that for a while each new Earth analogue will be announced everywhere, and perhaps that will generate interest in speculative exobiology as well ('Hey! We thought so all the time. Come and have a look at Furaha, Nereus, Snaiad and the others!').

'Alien planets revealed' is in part about the planet Kepler-22b, while 'Aliens: are we alone?' is about Kepler is about '701.04', or Kepler-62f, discovered later. The radius of Kepler-22b is 2.38 times that of Earth, and its mass is estimated to be 6.4 times that of Earth; for Kepler-62f the values are 1.41 times Earth for its radius and a mass of 2.8 times Earth. Both documentaries use the same image material to illustrate the consequences of a high gravity for legged locomotion, which is perhaps more apt for Kepler-22b than for Kepler-62f. Oh well, never mind...

Both might be 'ocean worlds'. Both contain a discussion of life in the seas, of which a short clip is shown above. While the text mentions the need for streamlining as something of universal value for a swimming animal, the animals are less streamlined that I would have thought. Perhaps, but I am guessing here, that is due to an unwillingness of the animator to give the animals a completely fish-like of dolphin-like shape. Even though that would make sense, the result might not look sufficiently alien anymore.

My attention was caught more by a discussion of life on land. A high surface gravity has been discussed in the blog more than once, which is not surprising as it affects so many design features of animals and plants (for instance here and here). The documentary is about walking, and high gravity can be expected to have at least four effects on the design of a walking animal.

Firstly, to minimise muscle energy expenditure you may expect pillar-like vertical legs. Any position with angled bones requires energy to keep the joints from bending. You can expect legs to become more vertical on a planet as animal mass increases, which is very visible on Earth. You would also expect animals with the same mass to have more columnar legs on a high-gravity than on a low-gravity planet; I may do the calculations one day to investigate how animal mass and gravity together should affect bone and muscle size. 

A second effect not directly found in textbooks, but which seems to make sense to me, is the 'zigzagging' of a series of leg bones: they will tend to angle forwards and backwards in alternating fashion (the principle is discussed here and here). The idea behind that is to keep all joints fairly close to a vertical line from the hip down to the foot: this decreases the leverage of the joints and again saves on muscle effort. 

A third effect is found in the number of legs. In a post entitled 'How many legs are best for megamonsters? For megamonster syou may read 'high mass animals on an Earth-sized world', but also 'medium maas animal on a high-gravity world'; the effects are very similar. I calculated the relation between the mass of an animal and the mass of all leg bones, assuming that each leg would support its fair share of the animal's mass. I was surprised to find that the least bone mass was needed if the animal had fewer legs, so theoretically one legs would be most efficient. However, that high 'efficiency' only holds true if less bone mass is the only factor to be considered. But there are other factors, and an optimal solution is biology usually represents a careful weighing of many factors. A larger number of legs would protect against falls and allows better survival chances in case of injury of a leg. In the documentaries, someone must have decided that this risk avoidance would be best served by equipping the animal with eight legs. I do not think that we know what the optimal number is, but meanwhile I have nothing against eight legs.
  

Finally, there are gaits to consider: there is an infinite number of ways to describe the order in which you can move eight legs in a walking cycle, but which is best? The safest solution is to move just one leg at a time, leaving the other seven on the ground. At the other side of the spectrum there are very fast gaits using just two legs: even crabs and cockroaches can run bipedally! But running can cause falling, and a fall on a high-gravity world may kill you. A safe solution is to always support the body by at least three legs, forming a tripod. So, based on safety and a guarantee that there must be three legs on the ground at any time, how many legs are needed?  It the animal has four and uses a lift-one-leg-at-a-time strategy, the puzzle can be solved. With six legs you can form the basic insect gait with two alternating tripods. That is shown above: note that the left and right legs of each pair move alternately, and each pair is exactly out of phase with the pair in front of it. The results are, going front to back, the left-right-left pairs move in unison, as do the right-left-right legs; but exactly out of phase, of course.

Are eight legs better? Well, it allows the animal to lift more legs at a time while still having three on the ground, and that can be done in various ways. Another solution is simply to expand the principle of the hexapod, and have the new pair of legs move exactly out of phase with the one in front of it. Each tripod becomes a tetrapod; a 'table' if you like. In the 'double table' scheme shown above you can lift and move each table and keep the animal perfectly stable and safe.

And here is the result of the documentary. The person doing the introduction is Lewis Dartnell, who once introduced Furaha at the Cheltenham science fair. Hi Lewis! The documentaries develop the same 'double table' gait through a genetic algorithm. That is fascinating, as it is based on a model taking many forces into consideration. The person who did those simulations, dr. Bill Sellers, has a very interesting home page on animal movement simulation. I had hoped that the genetic algorithm would have resulted in something a little more surprising than the double table that the old-fashioned logical approach predicted, but the double table does make good sense. I am playing with the idea of writing a genetic algorithm myself to see whether this is just one optimal solution, or whether there are several that are nearly just as good. Perhaps it will help to begin to answer the question 'what is the optimal number of legs for large animals taking lots of variables into consideration?.