Saturday, 2 September 2017

Spirally slanted spidrids II

The post has the simple purpose of showing that there is progress with The Book. Readers with good memories may remember that I write about spidrid gaits back in 2013. In one post, I toyed with the idea of changing the plane of movement of the spidrid legs from a purely vertical to an angled one. This was inspired by the legs of many crabs and by those of scorpions.

Click to enlarge; from Wikipedia
Here is a nice image of a scorpion from Wikipedia, showing that the plane of the legs is not vertical but at an angle to the ground.

Click to enlarge; from Wikipedia
And here is a 'sally lightfoot' crab (Grapsus grapsus) also from Wikipedia. Note that the hind legs are seen edge-on, so the plane in which they operate is at an angle of that of the surface on which it stands. 

This inspired a very lively discussion in the comments sections why the legs would be slanted. Among the possible advantages were that the animal would be less high, so it could fit in a crevasse among rocks, or it would be less likely to be swept away by tidal waters. Another argument was that the slanted posture allows more muscles to be recruited for propulsion.

Well, I can now add that I found some evidence for the latter argument, in Mantons's Arthopods (There is more on that book in this post). It is difficult to find anything on the biomechanics of arthropod joints. It seems that most of the relevant work was done in the 1960 and 1970's by Manton. In the end I bought a second-hand copy of her book, which proved to be one of the most densely-written science books I have ever read, but it contains an enormous amount of information. She wrote about 'rocking' of arthropod legs, the word she used for what I described as 'slanting', and her reasoning was that it recruited additiopnal muscles for propulsion. No formal proof though! It does not mean the other arguments are invalid though!


video


In 2013, I produced this quick and rough animation of what a 'spirally slanted sipidrid' might look like.  I recently sat down to do justice to spidrids in The Book, which means doing a few proper paintings with accompanying size diagrams and maps. I chose to add a slanted spidrid to the introductory page showing the variety of shapes spidrid bodies can take. I do that more often: designing various shapes is fun, and it nicely illustrates adaptive radiation. It also allows me to paint various colours and different surface textures.

Click to enlarge; copyright Gert van Dijk
Here it is. It is just a fragment of the original 4200x6000 pixel illustration, and is just meant to give you a taste, not to satisfy your appetite! As you can see, I chose to go with the shiny texture of the sally lightfoot, as well as its riotous colours.  The text introduces it as follows:

"Mad Sickle
This species represents a major spidrid clade. While ‘square spidrids’ move their legs in a vertical plane, the ‘slanted spidrids’ do not: the basic leg joints have tilted. The most likely reason for this is that the flexion and extension muscles can now more easily help with propulsion. Most ‘slanties’ are very flat and live in crevasses. There are clockwise and anticlockwise slanties; the direction is inherited, so each species has its own exclusive direction. It seems that the two types of slanties arose completely indepedently, so ‘clocko's’ and ‘antics’ are not at all related. The mad sickle is very agile. Please do not try to catch one: you disturb them, you are not likely to succeed, but if you should, it will pinch you very forcefully. 
Name Sicilicula insana; Sicilicula (L.): little sickle; insanus (L.): frenzied, maddening"

13 comments:

Petr said...

Wow! look at thast bright red and cyan! :D It really does look exotic and the slanted legs give it almost a propeller-like appearance.

I wonder why that surprised me so much, a spidrid would need to propell itself forward too. (whichever of the possible "forward" direction it decides to go, man, spidrids are fun critters!)

I love this so much!

Petr said...

Sorry for the spam,

I just wanted to add that spirally-slanted spidrids are definitely among the most unique and unusual-looking fictional creatures I have seen so far, and despite the complete lack of radially slanted creatures on our planet, they still manage to look right, very plausible and natural, as if they are really supposed to be like this, and it could even provide some additional benefits to the creature as well.

The spiral slant would allow them to fold their legs tightly against the body absolutely seamlessly in a way which is impossible to achieve for bilaterally symmetrical domestic arthropods. There would really be no obvious start or end to the compacted whorl of legs, meaning they would be really tough for predators to pry open.

Some desert spiders roll up into a ball to travel downhill and save energy (and possibly cool off in the process?) and a slanted spidrid would be a literal biowheel who could do this sort of thing like a breeze as well.

Sigmund Nastrazzurro said...

Petr: I saw 3 messages, but only 2 are posted. Is that on purpose? Thank you for your coments. Actually, after writing the post, I had the same thought about 'wheeling' spridrids. 'Slanties' would be very suited to tilting themselves on their edge and rolling off at great speed. This has ben done before in speculative biology. i caanot imagine that the animal would be able to se well while doing so, so cartwheeling' is probably bet reserved for a mad flight if there are no ther optiuons. But I can certainly see them doing that.

Anonymous said...

Splendid! An excellent addition to what we know - that Mad Sickle is. (and don't worry, I think only The Book will lessen our hunger)

I'll try to re-borrow that library book 'Walking Sideways' (i think its entitled), about the two sides of the crab family, how they move & everything.

(would cartwheeling be good for down a slope - like those Kalahari spiders?)
-Anthony Docimo

Petr said...

gert - Sorry about the confusion Gert, that third comment may be on the previous post from years ago. I re-read it, yesterday and the comments too, and I commented there again.

Do I spy a crab-like claw on each foot of the mad sickle, or are my eyes tricking me?

Anon - yeah, those are the spiders I had in mind as well

Sigmund Nastrazzurro said...

Both: the cartwheeling could be down a slope, but since the legs can move clockwise or anticlockwise with force, the animal can also cartwheel under its own power (even uphill!). I was tempted for a second to add cartwheeling to its normal array of gaits, but the fact that it would have trouble seeing kept me back.

I think those spiders were in the Kalahari epidsode of Attenborough's Africa documentary.

Anthony: thank you; I have started reading about kickstarter as a way to produce books. it sounds intriguying, in partiucuyaltr the parts weher you promise additional goodies for people to invest quite a bit; a model brotorusp, perhaps? You name on a species?

Petr; there are definitely claws there. In some, they are very slender as otherwise they would impair the function of the legs, but in others they are fully functional. The mad sicle certainly makes good use of its claws.

Anonymous said...

well, if the cartwheeling is reserved for emergencies, it doesn't need to see the entire time. (I'm reminded of learning - possibly apocraphal - that the tiger beetle runs so fast that it is actually blind while its racing...hence why it has to frequently stop: so it can look around for its next burst of speed)
-Anthony

Keavan Ѳ said...

Uploaded on the 2nd of September? By gosh, it's a birthday present from my favorite blog's author.

I imagine that spirally slanted legs could result in uneven forces and uneven traction. I wonder if the gaits of the "forward" and "backward" slanting legs would be that different.

GnorthernGnome said...

Fantastic work as always. Don't have much more to add to the spidrid debate but saw your comment on Kickstarter. I often wonder, when you mention The Book, if a Kickstarter or similar would be worth suggesting, so it's great to see you thinking about. Just wanted to chunk out my support for any such project!

Also, for what it's worth, if you are looking at going that route but don't want the deadline restrictions I'd definitely suggest Patreon. I've been very interested in how Darren Naish has been using the platform to fund his own Big Book (I'm sure you're aware of it).

Sigmund Nastrazzurro said...

Anthony: Do you think you can find the references concerning tiger beetles not seeing whole running? That would be interesting.

Keavan: happy birthday! I agree that slating might have different effects for different sides of the animnal, but decided that that is not enough reason to abolish the idea.

GnorthernGnome: thank you. At present I have just begun to read about kickstarter and its variants. Thanks about the hint about Patreon'I wil ask Darren why he chose Patreon.

Evan Black said...

Brilliant work, as usual! I love how sprightly and natural the Mad Sickle looks, and would love to see it in action.

I'm also intrigued by the idea of slanties folding their legs up tightly against themselves. This would certainly be useful in cartwheeling or rolling away from danger, but I could also see it as an effective way to protect against predators; consider armadillos, pangolins, pill bugs, and other creatures that roll up to protect themselves. A carapace covered in spikes (that are either fixed or foldable) would be another awesome adaptation.

Sigmund Nastrazzurro said...

Evan: thank you! Seeing the Mad Sickle in action... I can theoretically do that, as all the programming and imaging building blocks are in place. But it is so much work. I was well on my way several years ago: http://planetfuraha.blogspot.nl/2013/06/the-main-furaha-site-hasnt-seen-any.html

The reason I stopped developoing such realistic videos is that they require an enormous amount of work, and all that time is taken away from painting and writing. Still, I am sorely tempted to do a simple schematic animation using Matlab only. But before anyone says 'this looks familiar', that may be because not only are there cartwheeling animals in real life, but there is also Warren Fahy's 'ant disk', which I discussed previously. http://planetfuraha.blogspot.nl/2010/08/warren-fahys-fragment.html
There are similarities between many speculative biology projects, and, as discussed many times, there is such a thing as 'parallel speculation'.

Before these comments I had nog given much thought to slanties locking their legs with one another and with their bodies. I shouldn't really devote yet another page to spidrids, but perhaps I can squeeze one on the page about the as yet to be painted 'secondarily bilateral spidrids'.

Anonymous said...

I couldn't find the reference on youtube, but Nat Geo had this: http://phenomena.nationalgeographic.com/2014/02/04/tiger-beetles-become-blind-when-they-run/

whether cartwheeling comes before rolling up for protection, or rolling up arose first, I can picture both being quite successful with the Mad Sickle's relations.
-Anthony Docimo