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There are lots of examples in fiction of lizard people, bird people or beast people, but I'd like to expand my phylogenetic horizons in conceptualizing my world. To that end, I have conceptualized a race of large, sentient flatworm people.

I am not an artist so I will spare you an attempt as visualizing my idea, but basically imagine taking one of these wee beasties

a planarian flatworm

and scaling it up to be between two and three meters long.

Specific features:

  • Like all flatworms, they have no circulatory system, respiratory system, or anus. They are acoelomate (lack a body cavity).

  • All individuals are Hermaphrodites and lay small eggs.

  • They can reproduce via binary fission, but prefer not to, and this becomes extremely difficult as they grow larger.

  • Their eye spots are more developed than modern flatworms, but their eyesight is still very poor.

  • They have large brains with intelligence comparable to prehistoric humans, but they usually keep most of their neural tissue dormant to save energy and enter a sort of vegetative state while grazing.

  • They have no native language comparable to our own (although they do use unintelligible animal signals between each other), but some have learned to crudely mimic human speech using their foot (more on that later) and soft mouth-parts, which are located on their underside.

  • They eat mostly decaying plant matter but can hunt small, soft animals (they have no chewing bits).

  • They live in a moist, swampy environment and rely on oxygenated water saturating their porous tissues for respiration. They have to remain wet or they can't breathe.

  • They have no limbs or appendages but posses a muscular "foot" that gives them limited ability to manipulate their environment.

  • They are probably the largest animals in their ecosystem and would have no major predators. Fish or crustaceans might takes bites out of them every now and then, but they can easily regrow the lost tissue. And I doubt that they taste very good.

  • They possess the intelligence and dexterity to create crude dwellings from mud that they use for shelter during natural disasters.

  • While they have the potential to create a primitive civilization, most just spend their days lying in the muck sucking up pond scum.

Is this species, as proposed biologically reasonable? I'm guessing there are probably some surface-area-to-volume ratio problems that I haven't considered.

I'm primarily interested in getting answers as to whether or not my current proposal is realistic, but bonus points for suggesting solutions to make it possible should it prove to be impossible as written.

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    $\begingroup$ Flatworms are extermely simple animals. They have very few specialized organs so why would they have a very advanced brain? What you are describing is an early 20th century whale oil powered car which features a modern computer system for GPS navigation $\endgroup$ – SilverCookies Apr 30 '16 at 16:10
  • $\begingroup$ Huh, wasn't there a X-Files Episode about such a specimen? Right in the first season, where it lives inside the water tank of a Russian freighter? Can't remember the episodes name, sadly. Plus, that guy do not fit your requirements, but if want a... spooky impression, it might be worth watching that episode. $\endgroup$ – Confused Merlin May 2 '16 at 5:41
  • $\begingroup$ haha! cool idea. worm people is what fiction needs more of. $\endgroup$ – com.prehensible Dec 8 '16 at 18:12
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First, I have a nit to pick: you write, "They have no limbs or appendages but posses a muscular "foot" that gives them limited ability to manipulate their environment." Then that foot is a limb/appendage. Good, because they are going to need some characteristic that stands out (in this case literally) in order to evolve intelligence at all. Without it, what advantage does a smarter-than-average flatworm have over his less brainy fellows?

One can conceive of intelligence evolving without manipulative limbs. Dolphins have gone at least some of the way to doing this - but they are highly social and communicative, are both hunters and hunted, are mobile, and reproduce sexually. Lots of evolutionary incentives to get brainy and lots of ways in which one dolphin who uses its wits can be notably better at reproducing than another.

As presently described your flatworm people would do just fine with the brains of a… flatworm. Just keep happily slurping up the pond-scum or sleeping in the vegetative state you mention. That is, until some creatures with arms and legs come along and harvest these defenceless creatures to extinction. (The worms not tasting good won't be much protection. There are plenty of ways to use biological tissue other than food.)

I would like to glance at some of the characteristics you have given these people and look at ways they could be explained or changed to make a more plausible sentient being.

They have no native language comparable to our own (although they do use unintelligible animal signals between each other)

Who says their signals among themselves are "animal"? It may be unintelligible to you, human. But given what else they can do, it sounds like some other species is refusing to acknowledge the flatworm's intelligence in the teeth (so to speak) of the evidence.

but some have learned to crudely mimic human speech using their foot

You are doing them down, here. An appendage that can both build dwellings and have the fine motor control to mimic sounds is amazing. Again, you have to consider what caused such dexterity to evolve. What exactly do you mean by "crudely mimic"? Is the mimicry is just copying the sounds as a parrot would? Or do they respond to what is said to them and generate meaningful new sentences? If the latter, however badly pronounced it is, that's not mimicry, that's speech.

They have no major predators and They eat mostly decaying plant matter but can hunt small, soft animals

It seems odd that they could evolve intelligence when food basically falls into their mouths and they don't have to dodge anyone. Wait a minute… perhaps the reason that they have no predators is that got tired of having chunks bitten out of them by the larger ancestors of the crabs and fish you mention and hunted said predators to extinction. Maybe the folks who think the flatworms are just a source of cooking oil are in for a very nasty surprise. The question is how do the flatworms fight back? It could be via building traps, or some sort of poison their bodies emit, or better yet some sort of poison they harvest and mix together using their clever brains and dextrous foot/mouth appendages.

They possess the intelligence and dexterity to create crude dwellings from mud that they use for shelter during natural disasters.

Make the disasters frequent and terrible. Only the builders survive.

While they have the potential to create a primitive civilization, most just spend their days lying in the muck sucking up pond scum.

A thing worthy of explanation in itself. Whatever the explanation, given the requirements of fiction, I suspect that the Chronicles of the Flat Folk are about to become very much more interesting in the Chinese sense.

They can reproduce via binary fission, but prefer not to, and this becomes extremely difficult as they grow larger.

The likelihood or unlikelihood of intelligence arising in a species which reproduces in an asexual manner is a fascinating question which has also interested me and several others. But I must hope that someone else will address this because I am out of time.

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Actual flatworms don't need circulatory system, lungs, gills or anus because they are small (and flat) and oxygen and nutrients can pass through their bodies by diffusion. Diffusion is not very effective and it only can work for short distances and low requeriments. Therefore, the answer to the question whether this species is biologically reasonable as proposed is that it isn't, because the proposed species is not small and, since it's intelligent, it's expected to have sizeable requeriments on nutrients and oxygen to feed its brain activity and those requeriments can't be met by diffusion in a large animal.

Those drawbacks could be overcame by a circulatory system and other improvements, but then you wouldn't have a flatworm as proposed.

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  • $\begingroup$ Well, there's one saving grace on this regard: it's a flatworm. So long as the thickness remains the same, or only increases very little, it can get as big as it pleases and retain a diffusive respiratory system. Of course, three meters long by, let's say half a meter wide, and retaining a thickness in the millimeters will turn the "worm" into a "sheet". $\endgroup$ – No Name Mar 22 '18 at 23:54
  • $\begingroup$ @NoName You have a point, here. However, a large "sheet" without a circulatory system may find difficult to work as a single individual. $\endgroup$ – Pere Mar 23 '18 at 0:14

protected by L.Dutch May 2 at 2:09

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