Saturday, 22 October 2011

Lifting the cloak on Cloakfish

There is an odd difference between drawings and photographs of animals. In a photograph a galloping animal may be caught in time in just such a way that only one of its legs touches the ground. No-one will think twice about whether this is 'correct' or not. But do the same in a painting, and people will start thinking that the painter has it all wrong. Something like that happened to my Furahan Fish IV, shown in this blog earlier.

Click to enlarge; copyright Gert van Dijk

Here it is again. I received some questions where it right front fin had gone. Was it amputated or had I forgotten it? No, I replied, I worked out the perspective and the missing fin is simply hidden by the body. I admit that I saw these people's point and have been tempted to tweak the perspective a bit and have the tip of the 'missing' fin emerge from behind the body. Its absence seems to be disturbing in a way. While working on Fish and Cloakfish I experimented a bit with the reasons.

Click to enlarge; copyright Gert van Dijk

This image shows two versions of a ray-like species of Fishes IV. The top image shows a layer for the perspective lines as well as a layer containing some rough idea of light and colour. Layers, for those of you not familiar with computer painting programs, are the computer equivalent of a pane of glass on which you paint. The painting as a whole can consist of many such panes, each consisting a different bit of the painting. The trick is that you can make layers invisible, change their transparency or swap their order. I use Painter 11 as I like its tools, that resemble artists' brushes more than the tools of Photoshop CS5. As you can see from the sketch the perspective effect is fairly strong, meaning that parallel lines diverge quite a bit. Still, the drawing seems to work, perhaps because all parts of the animal are visible.

Apart from 'regular' Fishes, I have been working on Cloakfish, completely unrelated to Fishes I to VI. You will find cloakfish on the main Furaha page, but also here on the blog. Apart from a few sketches almost all my earlier work on cloakfishes involved computer graphics, because I wished to see their four 'cloaks' move while swimming. At present it is time to paint them, but I wished to get their cloaks right, and doing that by hand would be very difficult. So I took recourse to computer graphics, a process best described as 'practical' ('cheating' comes to mind, but why not use tools when available?). To help the process, I adapted earlier programmes in Matlab so I could produce a cloak with any shape I wished, as on the left, that is warped to produce waves progressing along it, as on the right. Right; make four of them, export them as 3D files, import them in a suitable 3D program (Vue Infinite in my case, and we are ready to play.

Click to enlarge; copyright Gert van Dijk

Here is an example. The left panel shows the four cloaks, striped to help visualise their 3D shape, attached to a central axis (that is called a 'dagger', by the way). The body proper is formed by some basic shapes such as cylinders and rectangles. I thought it might be worthwhile to put lots of parallel rods in the image that could help get a better feel for the perspective. I set the focal distance of the imaginary camera in Vue to 35 mm, and that is the image in the left-hand panel. The perspective looks believable, does it not?

The right-hand side was produced in Painter 11. I imported the image from Vue and painted a rough cloakfish on a semitransparent layer above it. I decided to play around with the front edge of the funnel. In that stage of their evolution, cloakfish were all filter feeders, so the opening in the front doubles as a food and a respiratory intake. Some cloakfish evolved feelers, and those are what you see here. I wasn't happy with the sketch though, and wondered whether the perspective was part of the problem.

Click to enlarge; copyright Gert van Dijk

So I went back to Vue, altered the characteristics of the 'camera' to give it a long lens, and repeated the process. Well, well. The result looked more suitable for an illustration that the earlier one, even though that one was realistic. More realistic, because the combination of the lens with the size of the animal resulted in a perspective closer to what you would see if you were a human on Furaha. Obviously, my attempt at 'mathematical correctness' did not work. Perhaps it can be as counterproductive as its political counterpart. Anyway, I was not happy with the funnel opening.

Perhaps it was time for a redesign. Should cloakfish really all be filter feeders? There certainly are small filter feeders on Earth (polyps etc.), but there is curious gap in size in filter feeders: either they are small or they are colossal, such as whales. I cannot think of sardine- or tuna-sized filter feeders. While I haven't thought that problem through, it seems a real one. I wanted cloakfish to occupy lots of niches and needed a good range of sizes. Perhaps the beasts needed a separation of alimentary and breathing tracts after all.

Click to enlarge; copyright Gert van Dijk

Here is an all-new cloakfish. The inner body protrudes forward from the funnel, that, as before, contains the gills. I played with it having four jaws, but decided against it. What you see here is the latest thing in cloakfish design: a regular mouth with a horizontal split. It need not stay that way, though. As you can see, their eyes have shifted forwards on the funnel to improve frontal vision while still having excellent all-round vision. And the perspective? Well, a view without strongly convergent lines, such as this one, may help viewers get a good feeling for the animal's shape.


j. w. bjerk said...

"I cannot think of sardine- or tuna-sized filter feeders."

Do you mean fish-like creatures specifically?

If not most bivalves, sponges and other water-sucking invertebrates, are sessile filter feeders. Various crustaceans are filter-feeders to one degree or another.

Many jellyfish and coral polyps use essentially the same feeding method. It doesn't seem to be of great significance that to that method that individual coral polyps are small and some jelly-fish are huge.

The crazy flamingo and "crab-eater" seal are too.

My guess is that for non-sessile creatures filter feeding is a highly specialized nitch, which relies largely on a few insanely prolific crustacean species, especially "krill". Under such circumstances it doesn't surprise me that different sizes don't have equal representation.

On Furaha, i think the behavior and commonness of the filter-feeder's prey would be the most important factor in determining what sizes of filter-feeders would work.

---As always an interesting read

Anonymous said...

glad to see you back. hope everything's settled down.

the ray-like Fish IV appears to have its lower jaw/tube lowered. a very nice detail to include.

I particularly like the size comparison picture. (the smaller two seem similar - same group of Fish, or paralel evolution?)

that's an interesting change to the cloakfish.

Spugpow said...

Awesome as always. I get a kick every time you reveal something new about Furaha, and I'm a huge fan of this behind the scenes stuff.

I have the same dilemma with "cheating". It isn't logical, but things like, say, motion capture in place of animation really annoy me. In this case however, it seems like you are using the computer not as a shortcut, but as a way to dramatically improve the quality of the picture :)

Regarding mid-sized filter feeders, two examples that come to mind are anchovies and paddlefish.

The cloak fish are so cool, they're definitely some of my favorite Furahan animals. That said, I'm not sure I like the redesign. The lumpy mouth doesn't mesh well with the almost machined-looking body, and the lack of radial symmetry strikes me as odd. in addition, the design is very similar to that of Earth fish and furahan Hexapods: personally, I think a more alien mouth arrangement would set these animals apart from the other creatures on the planet. Maybe manta-ray- like facial lobes?

Spugpow said...

You know, the mouth doesn't have to have tetrapartate symmetry. I think what bothers me about it is the asymmetry between the upper and lower jaws, since in a radial animal they ought to be identical.

Anonymous said...

if someone gives you a hard time about if that image had a fin missing, you could say "why yes, a predator bit it off."

(like sharks do to some sea turtles)

Evan Black said...

I was going to mention anchovies as well, but I'd also like to point out that while anchovies eat plankton they also eat tiny fish. Is it possible that at the size range we're discussing filter feeding is less effective and doesn't occur as an exclusive means of eating? Or is it possible that, as j. w. bjerk said, bivalves, sponges, etc. already occupy the niche so swimming filter feeders simply can't compete at that size?

"Cheating" as discussed here seems like a highly subjective and nebulous thing to me. I mean, I've used the exact same technique with almost all of my nereid illustrations; does that mean that I'm not a real artist? If an artist uses a wooden articulated mannequin, a still life or even a live model does that mean that they're cheating?

I don't understand the motivation for the redesign of the cloakfish's mouth. I don't necessarily see a problem with all cloakfish being filter feeders; it simply means that they're adapted well enough to dominate the niche in all their sizes and environments. If, however, you'd like to explore some radiative speciation then more predatory forms could certainly come about. The familiar horizontally oriented mouth doesn't seem very alien, but that doesn't make it implausible.

Sigmund Nastrazzurro said...

J.W., Rodlox, Spugpow and Evan,

Thank you for your comments. I tried to find papers on the size distribution of filter feeders but have not found anything useful yet. Possibly no-one has yet wondered about the best size for a filter feeder. I knew there were some more species when I wrote the post (I had ducks in mind). Bit look at predators: they come in sizes from microscopic to VERY macroscopic, with no sizes missing. This does not seem to be the case for filter feeders, in whom there seem to be large gaps. Perhaps there is no 'law' here but just a coincidence. I will try to find out more. In fact the new mouth could be a central opening within the outer, ring-like opening. It could then allow some cloakfish to be filter feeders while allowing other to be less restricted.

As for the present fish-like mouth, that is an experiment. The version just before that had four jaws/flaps, with the divisions vertically and horizontally. A major reason for changing that was that I just finished a series of Fishes IV, all with four jaws, so I felt like a change. That effect will wear off and then I will make a final choice for the cloakfish.

I do not really consider using 3D computer programs cheating. I once learned the basics of 'real' perspective drawing: it is a skill, but not the most exciting part of the work. Using a 3D program is like digital painting itself: you keep the creativity but gain time. Real cheating would be to take someone else's design and pretending it is your own. You sometimes see that happening with SF and fantasy book covers.

Jacob H Johnson said...

The paddle-fish comes to mind as an in between fish filter feeder. However, they are confined mostly to freshwater rivers, free from sponges and much of the other size extreme ones.

Sigmund Nastrazzurro said...

To all: I searched Google Scholar for filter feeder along with keywords such as mass, efficiency etc.

I have not found any paper that took both filter feeding by small animals (coral) and large ones (whale sharks, whales) into account. Several people wondered about why filter feeders make up such a large proportion of the largest sea animals, but without a definite answer. For the time being I can only guess at whether filter feeders are under-represented in medium-sized animals.
What that means for cloakfish is probably that there are no strong arguments against them being filter feeders.

Evan Black said...

Well then I think our best guesses are the best we have to go by. I stand by my theory that the niches of "mid-range" filter feeders on Earth are taken up by invertebrates, and so we don't see them among similar sizes of fish.

A species of note: the manta ray. It could potentially fall into that "mid-range" niche, at least compared to the larger end of the scale. Also noteworthy is the fact that it's the largest ray on the planet. Is there some sort of pressure for filter feeders to evolve into larger forms? Could it be the abundance of plankton, or perhaps some metabolic requirement, like how herbivores have large, complex digestive tracts to deal with plant material?