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I'm thinking of making a species that evolved in a planet that has a type of algae that secretes a nutrient rich sludge that the species only has to drink to survive. I know that this would make their digestive tract and internal organs vastly different than a humans, but what about how their mouths are constructed? I imagine that they might have a trunk instead of teeth and lips. Does anyone else have some ideas on how the mouth design would be?

(I'm also curious about if this would make them no longer have a nose. I don't know why it would, but I don't really know the evolutionary reason we have noses. So I have no idea in this matter.)

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    $\begingroup$ We have prominent noses simply because we lost our snouts. Essentially, our jaws lost their prominence but the nose stayed where it always was. Try to imagine a chimpanzee without his prominent jaws. $\endgroup$ – AlexP Aug 27 '17 at 21:21
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    $\begingroup$ Are you asking about mammals, birds, reptiles, insects, all of the above? $\endgroup$ – Monica Cellio Aug 27 '17 at 21:36
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    $\begingroup$ sounds like a mosquito to me... anyway the way we use our noses is very similar to mosquito, we all poke into other people businesses :> $\endgroup$ – user6760 Aug 28 '17 at 6:02
  • $\begingroup$ Please note that we encourage users to hold off on accepting an answer until some time has passed. This gives users who live in other parts of the world time to see a question and potentially provide a better answer. $\endgroup$ – Frostfyre Aug 28 '17 at 12:25
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Tapeworms have toothlike hooks to latch onto intestines from which to suck blood. Plecostamus eats algae but does so by scraping (so, something like teeth while not teeth.) Whales filter large volumes of seawater to 'harvest' enough krill to survive. They use baleen plates, again, sort of like teeth while not at all like teeth. I think you have latitude on the tooth issue, for your specific scenario.

I have more problems with the idea that the algae would secrete a nutrient rich sludge. If it were nutrient rich, I tend to think they would not excrete it. Most waste secreted by most organisms is not used by higher organisms (alcohol and other fermentation products being an exception). It might be closer to accurate to have the algae themselves be the nutrient rich food source.

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They would probably not have teeth, unless they evolved from an animal that had teeth, and the teeth were used in self defense or for some other purpose not linked to eating, such as digging to find algae. That being said, if you want them to have teeth, you can easily go with the teeth for self defense option and give them very prominent teeth.

A nose exists for breathing, so it would likely be unaffected, but if you want to avoid a nose you can give them the ability to breath from a different part of their body, similar to a whales blowhole or similar to gills.

If you want to give it a mouth you may have it feed through the use of its tongue, similar to an anteater.

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I'd suggest that the algae ARE the sludge. Lots of algae get pretty sludgey!

Your creature could be a filter feeder. Lots of options there:

  • Baleen Whales have lost their teeth and have baleen plates instead.
  • Flamingoes. Their ancestors lost their teeth when they became birds. Filter feeding came later.
  • There is a pterosaur which evolved to be flamingo-like in its feeding.
  • Various crustaceans, such as barnacles and krill use their legs to filter, then pass the food to their mouth. Some types of crab use special mouthparts which act as 'hands' to filter and again pass the food to the mouth.

Alternatively, they could suck the sludge up through a tube. Lots of insects do this to suck the sap of plants by piercing the stem - the tube is called a proboscis, if you want to google for pictures. Pretty much everything in the Hemiptera order have sucking mouthparts: aphids (greenfly), leafhoppers and the like.

A short guide to nose evolution in vertebrates... Fish use their noses for smelling, not for breathing. The amphibian descendants of those fish came out of the water also with a nose which was not involved in breathing. They had these pathways into the body:

  1. Nostrils --> nasal cavity.
  2. Mouth --> throat --> lungs.
  3. Mouth --> throat --> stomach.

This is inefficient - you can't breathe and have a mouth full of food at the same time. That's fine if you quickly swallow prey whole, but no use if you need to take time to chew before swallowing.

A creatures which was one of 'the early amniotes' (sort of intermediate between amphibians and proper reptiles) solved this. It evolved a pathway from nostrils to lungs, so it now had:

  1. Nostrils --> nasal cavity --> throat --> lungs.
  2. Mouth --> throat --> lungs.
  3. Mouth --> throat --> stomach.

So they could now breathe and chew gum at the same time! :-) All reptiles, birds and mammals are descended from that early amniote.

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