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