Alien para-tetrapods of Snaiad

Cor! Thanks, Darren!

Steak and Knobber Day among the Snaiads must be an occasion.

I've really enjoyed Nemo Ramjet's work. Apparently, he's going to expand on his terrific Dinosauroids project.

Great suggestion! Nice illustrations!
I'm addicted in Speculative Biology and Exobiology, and have my own creation, unfortunately I dont have the skills to draw them. Some of the were described in my blog (in Portuguese only, sorry), and the illustrations were made by my friend.

Awesome! This is really spectacularly well illustrated, time to add another speculative biology bookmark! In case anyone is interested in the links, other projects include Wayne Barlowe's gorgeous Expedition, and the remarkable Speculative Dinosaur Project, which is by this point an enormous web of interrelated resources from ammonites to the aforementioned dinosaurs.

Awesome! I didn't know about this, Darren, so thanks for pointing it out! I love spec-evolution.

I never expected you to post about Snaiad in your blog, since your blog only concerns Earth tetrapods. Thanks for spreading the word!

AWESOME! To me, Snaiaid is the best exobiology project out there, even better than Wayne Barlowe's Expedition. I love Snaiad because at first glance the animals on the planet seem Earth-like, but then it turns out that what we consider earth-like traits are either misguided anthropic assumptions or convergent evolution. For example while Snaiadi animals do have jaws and an endoskeleton similar to Earth tetrapods, the jaws are just modified genital sheaths and the skeleton isn't bone, but a wood-like hydrocarbon. Another example can be seen in the skeleton which has a pectoral armature similar to our scapular region, and a skid which is similar to our hips. But these bones are made of fused limbs from the Snaiadi animal's sea cucumber-like ancestor.

Also, Nemo Ramjet's Snaiad is very well thought out. The place looks like a real alien planet, with detailed and plausible ecosystems, alien anatomy, and evolution. My two problems with Barlowe's Expedition is that his alien creatures seemed to be utterly unrelated to each other, save for a few species like the Arrowtongue and the Rayback, and that many creatures seemed to have adaptations that seemed counterintuitive. For example, why would creatures who see through echolocation have luminescent patches on their body. But on Snaiad, you can see how all the animals (well, all the "vertebrates" since Nemo has said little on the non-"vertebrate" groups of Snaiad so far) are descended from the same basic "vertebrate" body plan, and have since radiated and adapted out into different niches, much like tetrapods on Earth.

You may be interested in this mystery para-cat in Britain:

http://www.youtube.com/watch?v=I0ZZLrs_g2Y

enjoy!

"since Nemo has said little on the non-"vertebrate" groups of Snaiad so far"

Actually, this has been debated a lot, mostly on the Speculative Evolution forums, and it resulted in several DA pictures. Groups other than "vertebrates" include arthrognathans, trikes and elastozoans

I know, but there is nothing cannon on thse groups, other than the names of the ones you mentioned, the fact that there are colonial trikes, red and green plants, and only two types of plants have been described, sprog and the pinnacle ranges.

Aside from the biology being well thought out, the naming is what you could actually imagine humans would call those things. Especially the fucker. Of course someone would call it that.

In expediation there actually is some correlation between creature. The arrowtongue and rayback might be a clade of cursorial predators, the springwing, keeled slider, and cragspringer are all a group of mountain-dwelling "herbivores," and the rimerunner and flipstick are both part of a clade of air-sifting monopods. The gas-filled floaters are also implied to be related, while the daggerwrist is strongly implied to be monophyletic.

"Monophyletic" just means "consisting of an ancestor and all its descendants".

Also: canon. A cannon is something else.

Sorry, that was a spelling error. I wish scienceblogs would let us go back and correct our posts.

The Fuckers irritate me. If not for that nomenclature, I could make a whole week's worth of lesson revolving around this in my 8th grade dinosaur/evolution elective. Brilliant stuff, still.

Keith:

the naming is what you could actually imagine humans would call those things. Especially the fucker. Of course someone would call it that.

Since the 'first heads' of the Snaiad animals are modified genitalia, they might also be called dickheads...

Dinosaur Teacher, just call them catalchids, that is the name I always use. And its a bit more appropriate, seeing as some of their other names are "catalchus" and "kuh". Their more...ahem...colorful name is more a local term than anything else, sort of like calling collared lizards mountain boomers. But the name has unfortunately stuck.

Gray, I can see that there are a handful of species that look related (I mentioned the rayback and the arrowtongue before), but their overall anatomy is highly divergent. I mean at least amongst tetrapods one can see similarities, even in the highly derived forms like snakes and turtles.

lame, it's too complicated to have two heads, those of you who have studied nonvertebrates know evolution has had plenty of chances to go in this direction (in bilaterian animals) and has not, the mouth is never far from the eyes which are never far from the brain, except in the platyhelminthes, which don't really have brains so that hardly counts

Also, why would the eyes and especially jaws ever occur away from the esophagus, and why would they colocate with the genitalia...think of what sort of unlikely transitional forms this would have entailed to evolve from simpler organisms

the mouth is never far from the eyes

You already mentioned Platyhelmithes. Which do count.

why would the eyes and especially jaws ever occur away from the esophagus

Supposedly, the Snaiad animals don't take in food through the "first head", so those are food-manipulating structures. Opabinia provides an example of an Earth animal with disassociated mouth and "jaws" - the anterior appendage isn't the location of the actual Anomalocaris-like mouth, which is on the underside of the head just behind where the appendage attaches.

why would they colocate with the genitalia

Again, at least one group of Platyhelminthes uses the sharpened copulatory stylet on their genitalia to capture prey.

Not to mention that due to some quirk of ontogeny, Snaiadi animals have serious trouble developing their secondary heads into effective feeding tools. The only exceptions are the tromobrachids, who "cheat" and fuse their arms into their second heads and act as mandibles, the advanced herbivores whose extended head is little more than a radula on a stick, and the jetocetes which have seriously screwed around with their anatomy, similar to how derived snakes and turtles are compared to other tetrapods.

And I agree with Chris, Opabinia is a perfect example of an animal whose jaws and mouth are not exactly the same. Another more "tetrapod-y" example could be considered the elephant, who uses its trunk to help it gather food, but then puts said food in its real mouth on its head.

It seems my confrontational style has elicited comments...

to Chris:Yes but...the planarians are about the simplest bilaterian there is, and may in fact be the exception that proves the rule. The fact that they have such a minimal encephalization (barely above the cnidarians) such that they can regenerate a head after it's been cut off the body, suggests that when things are that simple, it doesn't really matter where the esophageal terminus lies in relation to sensing organs and the brain. But just noting that encephalization increases with neural and other organismal complexity, one wonders whether there aren't specific evolutionary constraints at work as behaviors and structural complexity increase that favor a basic colocated esophageal terminus/(jaws, if you have them)/sensing/brain layout. I think this ignores the evolutionary history of jaws, for example- they're not something that organisms are just destined to evolve, and oh look, this organism happened to evolve them where their genitalia are. Jaws, loosely speaking (not specific to vertebrates) evolved in response to specific needs in relation to the intake of food. There isn't a reason why they would appear, along with the eyes, on something unrelated to food intake.
Anyway, this is an open question, and an interesting one.

As for elephants and opabinia, no denying that at some point it is useful to have probosces, but not at a basic level- these are specialists.

Nemo stated that the jaws aren't derived directly from their reproductive organs. Rather, they are derived from bony genital sheaths that originally evolved to protect the vital reproductive organs, and later when Snaiadi "vertebrates" colonized the land, the sheaths eventually developed into jaws, which are more food manipulating organs like tentacles, probosices, or arms than a mouth.

To see why Snaiadi "vertebrates" are built the way they are, one has to look at the group's natural history. The earliest Snaiadi "vertebrates" were nearly sedentary animals reminiscient of sea cucumbers. They lived in burrows their entire life, filtering food via their second head. Because they were so slow when they did move, if one left their burrow they would be easy prey for predators under normal circumstances. And so they developed an odd system of reproduction, putting the genitals on a stalk and extending them out of the burrow and along the sand, searching for mates. These stalks eventually developed primitive eyes, so the organism could sense where its reproductive organs were going, and could thus easily find other burrows of its species. The genital sheaths evolved to protect these important organs from the rough sand and such. When Snaidi "vertebrates" colonized the land, the genitals were the forward-most part of the body. As for the brain, it is rather close to both heads. That little brownish "lump" by the second head in the anatomy picture is its brain, and it is very close to the true mouth. It is also relatively close to the second head, if one takes into account the "gular sac" is between the two.

AD:

the planarians are about the simplest bilaterian there is, and may in fact be the exception that proves the rule. The fact that they have such a minimal encephalization (barely above the cnidarians) ... suggests that when things are that simple, it doesn't really matter where the esophageal terminus lies in relation to sensing organs and the brain.

I'm not really interested in seriously discussing the potential anatomies of entirely hypothetical organisms, but here's another real-world exception to the 'eyes are never far from the brain' idea: box jellyfish. They have even less encephalization (i.e., none) than planarians, but some of them have eyes. Up to 24 of them, in fact; they are of different types, and include rather sophisticated camera lens eyes.

I don't know that the requirement is so much for having them close together as it is for having them all towards the front, if greater encephalisation encourages more directional movement.

Yes but...the planarians are about the simplest bilaterian there is, and may in fact be the exception that proves the rule. The fact that they have such a minimal encephalization (barely above the cnidarians)

You're confusing Plathelminthes and Acoela. :-)

You're confusing Plathelminthes and Acoela. :-)

No, I think AD is speaking in terms of morphological complexity, not phylogenetic position. Platyhelminthes sensu stricto still have a very simple organisation. It may be (probably*) secondarily simplified, but it's still comparatively simple.

*I'm hedging my bets here.

Don't scallops also have rings of primitive eye-like light sensing organs around their bodies?

Dartian- the box jellyfish has sophisticated eye structure, but they still have a decentralized, neural-net nervous system (so we think, I guess). And they're not bilaterian. So perhaps it is not just organismal complexity, but organismal complexity within a bilaterian bauplan that encourages greater encephalization with greater complexity (and organismal complexity tends to reach its peak in bilaterian organisms). So I would argue that the jump from simpler ancestors to more advanced bilaterian descendants wouldn't have happened without greater encephalization. Also I find some of the features of early snaiadi evolution implausible, such as the evolution of eyes to see where its gonads are going...chemicals are simpler, why don't they just burrow to their neighbors if they're that close together, most benthic, sessile organisms today face the same problem and none have really evolved anything this extravagant...

Chemicals would be swirled around by tides, so yes the animal would know there were mates in the area but not nescessarily where they would lie. This was probably what early forms did, but eyes became an advantage and since nothing else really had them and the genital stalk was a good candidate for its placement. The environment and situation allowed for something uncommon on earth to flourish and continue to do so. Think of the benefits of animals being able to eat and watch for predators at the same time. A significant eye distance from the brain is seen in snails. http://arachnophiliac.info/burrow/gallery/snails/images/snail_anatomy.g… So if you must, picture the first head of tetrapods on snaiad to be eye stalks that manipulate items and store the gonads. If there are niches to fill, what ever group of animals evolves an advantage to fill those niches first will radiate, no matter how strange that animals methods of adaptation will be. There could be down sides to the anatomy but some sort of benefit will come up. Think of how tetrapods on earth breath and eat from the same opening, would't it have been more advantageous to have it seperated in order to prevent choking, probably, but thats not what happened. There's cephalization on Snaiad it just is slighltly different. Life isn't going to follow the same path as Earth on other planets, theres convergent evolution but some oddities will surely arise.

No, I think AD is speaking in terms of morphological complexity, not phylogenetic position.

So do I. Actual flatworms have more of a brain and even better developed nerve cords than acoels.

the box jellyfish has sophisticated eye structure, but they still have a decentralized, neural-net nervous system

Yes. To be precise, there are two motor nerve systems: one consisting of one ganglion next to each assemblage of sensory organs -- four "brains" connected by a ring from which nerves go up into the bell to the locomotor muscles; and a completely separate system for the mouth apparatus.

why don't they just burrow to their neighbors if they're that close together, most benthic, sessile organisms today face the same problem and none have really evolved anything this extravagant...

Barnacles do: they use a monstrous penis for internal fertilization while being sessile. I have no idea how they find out where to stick it, though. Tactile cues? Random?

I dunno, I still feel the Snaidi bauplan is somewhat contrived, weird for weirds sake, which may have been the point without putting- make people thing 'what else' might be possible. However evolution is not a random collection of natural histories...to some degree the natural history of an organism will constrain into what niches it is able to radiate. Also the whole breathing/eating out of the same tube problem just might be overstated- doesn't really seem to be a major mortality factor for most tetrapods :).
RPH- not sure how much chemicals are used by marine organisms, but obviously pheromones are used often by terrestrial animals...could also release eggs/sperm into water like shellfish and corals, or something..how do peanut worms mate?
DM- I actually said planarians, and if you look at their wikipedia entry I think what I said is accurate..

"Planarians" are paraphyletic, and acoels are not flatworms. I deliberately avoided the term "planarian".

We have to remember that Nemo is only human, and thus can't be expected to create the life of an entire planet that is completely plausable, but god damn has he come close. The universe is going to throw some strange organisms at us in the future and where all going to be like "how the heck did that thing ever survive?", what we need realize as well is there probably alot more about the evolution of animals on snaiad then what the website tells us and thus we should hope Nemo has reasons behind is chosen body plan. Theres so much we don't know, so we must be patient and not automatically critical. This is speculative biology, so it's all theory, and it's fun, something to stir up the imagination. Nemo has done something that is so in depth and to such a scale that previous attempts pale in comparrison, and that is why it is amazing, and thus any small negative critcisms are yes, important, but pale in comparrison to the achievements this project has generated. To put it bluntly, I love Snaiad. A lot. And for all its possible flaws, the things it has brought to my life and the lives of others and hopefully future fans are worth those flaws.

This is speculative biology, so it's all theory

No, speculation. :-) "Theory" means something else.

"Chemicals would be swirled around by tides, so yes the animal would know there were mates in the area but not nescessarily where they would lie."

Not to mention that the original Snaidi vertebrates were living in shallow water areas, ones where the chemicals would be easily scrambled by the tides.

Also, remember, Nemo never said that these eyes were necesarily complex. They could be very simple eyes or light recieving organs in the ancestral species, and once Snaiadi animals became more mobile organisms, the eyes could have become better developed in order to see.

"why don't they just burrow to their neighbors if they're that close together, most benthic, sessile organisms today face the same problem and none have really evolved anything this extravagant..."

They aren't sessile. They just leave their burrows very, very rarely, being so slow that most of the time they would be eaten up by predators.

I also realized something regarding the comment you made, AD, about the Snaiadi animals being specialized and not generalists. Not all life on Snaiad has two heads, just the "vertebrates". From what Nemo has said the other groups of Snaidi animals have only one head.

Plus, we all seem to ignoring an easy way in which a semi-sessile organism could develop eyes. They could be like sea squirts, having free-swimming larvae with a good sense of sight to see where they were going, and later mature into slower-moving, burrowing adults that almost never leave their burrow. They then would retain their eyes for the mating purpose.

GBA on the SE forum recently came after me on my comment about the Snaiadi "proto-vertebrates" eyesight. Contrary to what he said, I did not say that the animals eyesight became weaker with age. I merely said that Snaiadi animals could have primitive eyes, later becoming complex, or if they had complex eyes in their "cuke" phase of evolution, they could be because they used them for navigation in a free-swimming larval phase as well as mating. I never said that they weren't originally used for finding mates.

Wow, That was a slip up, didn't mean theory at all, but you do get the gist of my point I hope.....

I must've misread, sorry. It is an interesting idea though.

Thank you GBA. I was thinking of the idea based on the modern sea squirt (who, incidentally, is the closest non-chordate ancestor of vertebrates), which has a sessile lifestyle as an adult, but is a free-swimming larva as a juvenile. I was suggesting that the eyes could have originally evolved for the purpose of mating, but the reason they developed eyes as opposed to chemical sensory is that the eyes were also beneficial in the more mobile larva state, where sight was helpful in avoiding predators and finding food.

AD, I do agree that the "tetrapod-esque" body shape (as in jaws on the anterior end of the body, and several pairs of limbs) is the one seemingly most successful on land so far, and to an extent in the water, but you have to realize the Snaiadi animals to have a tetrapod-esque shape, albeit one that is "constrained into what niches it is able to radiate." Two problems faced proto-"vertebrates" as they moved onto land. One, the mouth was not in a very anterior position, it was farther back on the body. Instead the gonads and other mating utensils were at the forefront, sort of a reverse of what tetrapods do (rather than the gonads going posterior, they went anterior). I suppose a "sort-of" example on Earth would be squids, who have a breathing tube further back on their belly, but replace the breathing tube with a mouth and make the beak dead-end into the...development chamber...thing. Two, Snaiadi ontogeny has prevented the second head from developing effective jaws easily. Simply put, it is easier to develop the jaw sheaths of the first head than the second. Snaiadi animals that do have "jaws" are highly derived and have either screwed around with their anatomy so the second head goes into the first head, they "cheat" by fusing their arms with their second head, or they use the "radula on a stick" method.

MR- When I said "constrain the niches they can evolve into", I'm saying that the Snaiadi ancestral two-headers would not have been the ones most likely to evolve into more advanced, active, complex, or terrestrial organisms within whatever clade they originally fell into. I just think that already you are throwing together too many advanced things together to get the snaiadi bauplan to begin with. It treats major evolutionary innovations too lightly. It's also telling that no animal on earth seems to have evolved a mouth on a stalk, although probosces abound. And then it only gets worse with the two heads- a very ungainly setup. How the heck does it see what it is eating? It has to model in its brain where the eye-head is, then observe with its eye-head where its mouth head is, model that, calculate where to go next with the mouth, and back and forth- seems to be an advanced cognitive structure. By comparison, with eyes near mouth (physically attached) the eyes and mouth always have the same frame of reference. At most, the brain must coordinate a limb or proboscis to go out and get something and bring it back to the center of that constant frame of reference.
It is even worse if you consider the Jetocetes and the animals with spikes between their rear legs- clearly an attempt to be provocative with the latter (It seems counterintuitive to have to expose the entirety of the soft underbelly to defense mechanisms just to drive home a spike- you are already in range of other limbs at that point, it's like why do you need to go the extra mile to kill things with the part of you least extensible toward prey), and with the former, it's just not clear to me how that works. Please don't tell me they've invented rotary motors, but I didn't find the explanation of the mechanism on the website.

I would hope next time someone tries to make up a weird fauna to play devil's advocate about our preconceptions of what alien life might look like, they or someone else also plays devil's advocate by asking what reasons there might be why life did not evolve on this alternative path on Earth, and what reasons there might be for why evolution took the path it did.

I don't think chemical signals are useless in water. If you are centimeters away, you have to consider the scale at which turbulence would completely disrupt a diffusive or mixing-related chemical gradient -probably at larger scales than centimeters (unless you are in a narrow tidal channel or something). There is also something called a benthic boundary layer, below which turbulence is dampened. This gets into fluid dynamics which I am not an expert in but I think chemical homing would be easily possible in this context.

DM- acoels are flatworms, and yes, planarian is paraphyletic, but still a useful grade, and I used it with that intent.

acoels are flatworms

No. They are the sister-group to all other triploblastic animals together (followed, incidentally, by the nemertodermatids, as was published in 2002). Flatworms are lophotrochozoans.

Haikouichthys was the closest ancestor of all the craniates (including vertebrates) we know today. But what if something, dosen't matter what that would be, stopped chordates from becomming dominant, and instead, vetulicolians, radiodonts, or onychophorans took the lead? There are many other factors that would affect the evolution of alien life. Yeah, there might be some restricting features that may stop a radiodont from becomming terrestrial, but the resulting line would be still be quite strange. While there may be some similarities with life in our timeline owing to convergent evolution, that dosen't mean totally strange adaptations would not occur.

It is simply, in my opinion, arrogant to think that the way evolution happened on our planet, because there were many great splended anatomical inventions on our planet, our feeble brains will think that life will be anatomically the same on other planets, no matter how different its conditions are. There will, again, be many similarities owing to convergent evolution, but there will be many extreme differences that will take time for us to understand.

AD, not all of the information about Snaiad was given yet, but you are making one mistake; you are ignoring mass extinctions. Mass extinctions impacts evolution to such a degree that the downtrodded synapsids on Earth, now no longer suppressed by fluffy reptiles, gets the upper hand in taking 'superior' niches in the next several million years. Now imagine if the K-T extinction event never happened. Visit the Speculative Dinosaur project.

But back to Snaiad, the ancestorial 'vertebrates' coexisted with many more terrestrial species, terrestrial arthrognathans, red plant animals, and mullojiformes, but even with them dominant, they evolved certain adaptations that in the long run would eventually lead them to become dominant. The terrestrial ancestors of modern "vertebrates" were wormy in appearance, resembling wierdo onychophorans. They were just beginning to fuse their many hydraulic stubs into hydrocarbon 'bone', hydraulic muscles, and essentially, new limbs when the dominating terrestrial animals finally became extinct. Then they were left with themselves to take terrestrial niches.

A proboscis is essentially a stalked mouth. It is an elongated feeding appendage. We have plenty of flexible stalked mouths on our world, one notable example being how the giant triton extends its proboscis to use its radula to crunch into the carapace of its crown-of-thorns starfish prey. That creature dosen't have good eyesight as far as I know, but it still knows what it is biting into if it extends its proboscis, right? You really don't have to see what you are feeding on when you could just taste (and perhaps smell) and feel your food with your second head tongue. If you want to see what you are eating, you could always bend your first 'head' down to watch what you are eating. And if you look, the two brains (both fibrous and endocrine) are actually close to the mouth. Also, the nervous system of an animal from Snaiad is different. You shouldn't impress Terran neurology upon Snaiadi animals. I'm not sure how different it is, however, there is still a lot of things we do not know about Snaiad.

As for the fututoriforms, as Freudian as their pelvic spikes may look, they are actually a splended adaptation. Simply "humping" their prey to death isn't their primary means of attacking. Their pelvic spikes evolved from an extention from the hips, as well as a keratinous reinforcement. It is good for puncturing the hydraulic muscles of their prey, and without fluid for their hydraulic muscles to work with, they will become limp. That is when tackling a large animal. Now for animals their size, they would beat their prey to the ground and then possibly stab their legs to stop them from fleeing and then possibly stabbing vital spots on the body to finish them off. However, there are animals that have defensive features against fututoriforms, such as a rear spike or armored plates. Even the rape turtles' nasty pelvic skid isn't their primary weapon. They most of the time simply crush their prey by jumping on them. To refresh your memory about natural selection, some features of a creature may not have any effect on its survival, and yet still be passed down, and then eventually become a beneficial trait generations later. Because their pelvic region does not house any genitals, it was possible for a horn to protrude from the skid, and then eventually become a weapon.

As for jetocetes, I'm not entirely sure how the digestive tract fused into the first 'head', but it could be a result of the stomach dividing into another chamber that became a pump for creatures to propell themselves with when fleeing predators, while still primarily using their flippers. Then as the digestive tract rehooked into the first 'head', this pumping chamber became the main jet tract that is used for bursts of speed, without having to empty the stomach contents.

It is indeed normal to be terracentric about alien life, as planet Earth is the only life-bearing world we have had experience with. But imagine you were part of a species who lacked eyes. You hear "A creature has hollow balls that recieve light and create an image that we cannot imagine." and a skeptic would think "Oh psh. I don't think alien creatures will need such bulbs when creatures on the planet I live on do perfectly with sonar."

I personally think projects like Snaiad should be approached with curiosity rather than skepticism. For one, Nemo still hasn't given out all of the information of Snaiad in-depth yet, so it would be better to keep asking questions rather than being skeptical. Until we can finally prove what alien life would look like (id est, directly observing it with a probe in the future), I think we should enjoy what wild ideas we can think up of for now. Most likely, life is going to be strange out there, though, once again, there may be similarities owing to convergent evolution.

AD -
>It's also telling that no animal on earth seems to have evolved a mouth on a stalk,

the anteaters and worms (and some fishes) weep at what you have said.

In the linear sense I am using, a proboscis is an elongated flexible and/or extensible feeding aparatus. But generally speaking, a proboscis is any extended mouth of some sort, in the case of animals like anteaters and syngnathiformes. What worms are you referring to? Please specify a taxon, as a worm can be anything slender and elongate.

ok, just a couple things -DM-enter "flatworm" into Wikipedia, it comes up as platyhelminthes. Lophotrochozoa is a higher order taxon, including many phyla, including platyhelminthes.

Anteaters just have an elongated head, not a mouth on a neck, which is what I was meaning by saying "stalk"- and it doesn't argue against my central point, which is frame of reference problems, since the mouth is always the same in relation to the rest of the skull (also, extensive mouthpieces like some groupers are just that, extensible limbs going out and getting something on a predetermined, stereotyped, brief pathway mapped out by the animals brain). Also I don't know what "some fishes" are so I can't address that, but I sorta doubt that either anteaters or fish are "weeping".

I'm tired of debating this, and I don't believe I need a "refresher" on natural selection, or the other two basic mechanisms of evolution, drift and mutation. And no need to lecture on mass extinctions. But I would just like to say that far from being free from biased assumptions about how evolution works or free of earth-centric bias, assuming that life will randomly take on the most intentionally bizarre forms imaginable DOES make assumptions about how evolution works and how 'limited' evolution was on our own planet. For one thing, it views evolutionary innovation as "cheap"-not costly in terms of special conditions it takes to evolve new forms, or in the rareness of truly novel basic structural innovations, of which there are dozens among the snaidi (look at one of those phylogeny sketches..)
I also disagree with the implied notion that the course evolution took was nothing more than whoever didn't have a chair when the music stopped- that organismal variation is essentially neutral in the long term and differential survival and radiation of major groups on Earth is nothing more than random chance (essentially, drift at the bauplan level)...and thus we can expect something as bizarre and variable as Snaiad on another planet. Snaiad has it right in emphasizing the importance of historical contingency in influencing the subsequent form of evolution but I feel it fetishizes this concept and forgets that some forms are unlikely to evolve (innovation at that extreme level is rare) or are simply not liable to radiate into certain niches, even if the top dog in that niche is knocked off due to extinction. I digress...but anyway I just think the null hypothesis that evolution may have had reasons for following the broad-sense path it did (aside from mass extinctions) should not and can not be dismissed as mere earth chauvinism.
Signing off,
AD

Alas, if you think Snaiad is so absurd, you could always take it up to Nemo Ramjet.

From the Questions page:

"I think something is wrong with these animals.
This is, after all, a speculative project but I try to make it life-like in every aspect. If you still think there is a serious error, write me at *Nemo Ramjet's e-mail* and I'll respond."

But it is still a project that glows of excellence and scientific accuracy, no matter what terracentric criticisms are thrown against it.

But I must be speaking to thin air right now...

ANYway, since that's out of the way now, we can go back to nice discussions. The next update is likely going to be about the invertebrates. I simply cannot wait!

DM-enter "flatworm" into Wikipedia, it comes up as platyhelminthes. Lophotrochozoa is a higher order taxon, including many phyla, including platyhelminthes.

Yes -- and Acoela (like Nemertodermatida) is not a member of Plat(y)helminthes, even though it was thought to be one till a few years ago.

(late to the party)

thanks for diverging into the speculative, Snaiad is neat.

Somebody needs to pass the word to Nemo Ramjet though, that his main page

http://www.nemoramjet.com
is throwing a "file not found error". Looks like he doesn't have an index page.

The Snaiad website and subpage on his site are still up, and he has said that the website is being redesigned, but still, the length the site has been down is troubling.

I've been absent from the discussion that has been occuring here, but I think its ilogical to assume life on other planets would assume the same path than on earth. Evolution happens at random, its not designed, and ultimately the proto-eyes developed the primitive sea cucumber like snaiadi "vertebrates" could be pre-adaptations that occured without any specific reason and happened to be usefull (eyes might not be extremely necessary in imobile aquatic organisms, but they aren't useless either)

DM- apparently one paper in the Canadian Journal of Zoology makes the claim that Acoela do not belong in the Platyhelminthes, but rather are basal to all Bilateria. In this case, they would NOT be Lophotrochozoa. Nonetheless, one small paper does not a conclusion make, and I don't know species names of Acoela, but a definitive phylogeny,
http://www.nature.com/nature/journal/v452/n7188/pdf/nature06614.pdf
has Platyhelminthes as monophyletic.

Anyway, this is still all irrelevant to the context in which I first mentioned them.

Carlos-- evolution may not be designed but it is constrained, by past evolution, likelihood of reaching a given endpoint relative to other, simpler paths, by population genetic processes, myriad types of benefit/cost tradeoffs, etc.
Anyway, thanks for the vigorous debate.

apparently one paper in the Canadian Journal of Zoology makes the claim that Acoela do not belong in the Platyhelminthes, but rather are basal to all Bilateria.

Several papers on molecular data and on neuroanatomy got this result, starting with a science paper in 2001.

In this case, they would NOT be Lophotrochozoa.

That's exactly what I'm saying: the flatworms are lophotrochozoans, while the acoels are not.

a definitive phylogeny,
http://www.nature.com/nature/journal/v452/n7188/pdf/nature06614.pdf
has Platyhelminthes as monophyletic.

There is no such thing as a definitive phylogeny.

This one in particular was made using a method (alignment and phylogeny reconstruction in one step) which has fared very badly in simulations; indeed, the tree contains plenty of weirdnesses, some of which are clearly wrong. There's probably plenty of long-branch attraction in it; the position of Tardigrada mentioned in the abstract is most likely a case of that.

omg, ok. dm, you need to look at how i originally used the term flatworm. i am not interested in having this argument.

i know there is no such thing as a definitive phylogeny, but what is a one-word way of denoting that a given phylogeny is more trustworthy than one based on a few genes, for example?

"The latest paper on the subject"? "The biggest analysis so far"? I use that kind of expression all the time.

(And this particular analysis isn't terribly trustworthy, because its method isn't. There was half a Systematic Biology issue devoted to that fact... January 2006, I think.)

My point is that you shouldn't use "flatworm" to talk about both actual flatworms and acoels.

also, i wouldn't make claims about phylogenetic methods that you don't back up, if the preponderance of evidence isn't on one side. LBA is a special case of artifact, you will always have it unless you break up the branches or use a better model of sequence evolution that accounts for it.

Also, http://www.nature.com/nature/journal/v452/n7188/full/nature06614.html#o…

it appears they did NOT use a one-step alignment/phylogeny calculation, they were separate steps.

Again, all this is irrelevant to the original context, which was when morphology/neuroanatomy/etc is as simplified as it is in flatworms, it may not matter where the mouth is in relation to the 'head', but in other bilaterian organisms, somewhere along the way this characteristic is no longer preserved.

actually, i didn't notice this before, but from the genomic phylogeny the 'flatworms' or 'planarians' are quite paraphyletic- as you are saying, platyhelminthes does not include acoela, but again i don't think it changes the basic argument i was making...i think

Back to the whole eyes and genital stalk thing, I'd like to note that the vast majority of near-shore benthic burrowing invertebrates like the proto-tetrapods of snaid are either broadcast spawners or locate their mates chemically. It's certainly effective to use chemicals in these conditions and vision doesn't work particularly well. Chemicals spread beyond line-of-site, and vision is often limited by depth, nightfall, or turbid waters. I'd argue that identifying and following chemicals is easier than using vision, too. Still, I don't find Snaid's first heads to be too outrageous, as stranger things have happened on our world. Perhaps the use of vision was promoted as a form of sexual selection (always a good excuse for counterintuitive traits)

....or maybe all this unlikely weirdness is just evidence for the intelligent design of Snaid's lifeforms. The world may never know...

Very distressing news:
www.snaiad.com appears to have been discontinued, since the domain name is for sale. Any ideas of its new whereabouts/what happened?

www.snaiad.com was just a redirect to http://www.nemoramjet.com/snduterus.html

This is where the meat of the site was, and it's still up.

More wow. When I have time to visit, I will! thanks for the info.

This guy will tell you the whole reason heads evolved is because of jaws:
http://rosslab.uchicago.edu/people.html
http://rosslab.uchicago.edu/research.html

"www.snaiad.com was just a redirect to http://www.nemoramjet.com/snduterus.html"

Unfortunately I tried to access that site and it was invalid.

It would appear that Snaiad.com has vanished from the interwebs. Does anyone have another link?

Anyway there are some of Nemo's illustrations up on deviantart.
Link: http://nemo-ramjet.deviantart.com/