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Currently, I am designing a sapient species whose only dextrous appendages are their prehensile mouthparts.

I am aware that there are some issues with this, but I can think of ways to avoid or comfortably handwave away all but one of them: The issue of hygiene that comes from having to put your mouth on everything you want to pick up.

In short, the title pretty much says it all; How can a species whose only body parts with significant dexterity are their mouths avoid contracting infection diseases too easily to plausibly build an industrial civilization?

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    $\begingroup$ Have really good immune systems? They did evolve with those mouth-parts. Presumably as kids they will be a billion tines worse than humans at putting random objects into their mouth.... $\endgroup$
    – sdfgeoff
    May 4, 2022 at 7:50
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    $\begingroup$ What is the design of these prehensile mouths? Are they like an elephant's trunk, or are they like the adapted legs of a crab's mouth parts? Maybe a drawing would help. In any case, both elephants and crabs seem to survive pretty well. $\endgroup$ May 4, 2022 at 13:26
  • $\begingroup$ Have you seen giraffes? They're some of the best examples of what you're looking for, with dexterous lips and an equally dexterous tongue, as well as special adaptations to deal with wounds and infections in their mouth. All due to their diet highly based on the leaves of very spiky trees. $\endgroup$ May 11, 2022 at 1:15
  • $\begingroup$ Seems to have worked out okay for Pierson's Puppeteers. $\endgroup$
    – Zeiss Ikon
    Oct 3, 2022 at 18:05

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Most animals do a lot more handling of items with their mouths than we do, because the human quirk of having kept two limbs aside for non-locomotive activities is pretty unusual. So overall you are probably worrying about this too much - grabbing things in your mouth is the default.

However you can also look at the specific examples of animals that are unusually dexterous, unusually filthy etc.

  • Elephants use their trunk for manipulation; you can argue that getting noxious stuff in your respiratory tract is far more dangerous than your mouth, since you don't have the additional security granted by teeth, stomach acids etc. They have lots of both strong and delicate muscles that help them control the flow and pressure of materials inside their trunk (e.g. if they have filled it with water for spraying or drinking). So you could have an elongated appendage (Opabinia-style) that connects the manipulating "lips" to the mouth, and increase the control layers in the "tube" part to reduce the chance of unwanted content.
  • Vultures eat really grotty stuff. They get away with it by having ridiculously strong stomach acids (pH 1) but also by making sure that delicious but admittedly pretty putrid bits of lunch don't stick to their feathers, by having bald heads and necks. Both of these aspects could be applicable - corrosive digestion, and hairless/featherless mouthparts and surrounding areas (maybe even actively slimy?)
  • Hawk-moths (and many others) have specialised mouthparts for feeding on trumpet-shaped flowers, resulting in a thin, tube-like proboscis longer than their body. You could have a similar specialisation extending from the inner part of the digestive tract, such that when members of your species need to eat, they extend this long "straw" feeding straight into their gut, while the "outer" mouthparts, lips and maybe tongue, are used only for manipulation (and have actually no access to the digestive tract). You would be limited to eating liquid, possibly highly-processed food, which may factor into their industrialisation and society.
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Don't overestimate the role of proper hygiene in the wild, there are plenty of animals who practice rather unhygienic habits:

  • chickens and birds in general seems to have no problems in feeding among their own droppings
  • some animals feed on rotting corpses
  • horses seems to feed on dog dropping, when the dog has eaten carb rich food (and then they risk dying if the droppings are wrapped in a plastic bag by the dog owner)

Basically, you should worry about your manipulatory appendix hygiene only when and if the place from where you are taking the object to manipulate is clean/safe enough. Washing hands before taking something out of a fuming dung pile won't make much for safety/hygiene.

It's up to an animal's immune system ensuring that such threats are contained and do not bear too much damage.

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    $\begingroup$ I am very skeptical about the horses-eating-dog-poo thing, the only source I can find for it seems to be a second-hand report in a tabloid. And from personal experience of horses and dogs, horses are decidedly not interested in dog poo and unlikely to consume it either accidentally or deliberately. Horses will occasionally eat horse manure, but even that isn't super common. If anything, you are looking for the opposite--dogs eating horse manure is very well documented (also dogs eating cat poo, or dogs poo from a large variety of other species, or dogs eating really almost anything). $\endgroup$ May 4, 2022 at 20:34
  • $\begingroup$ "dogs eating cat poo". Can (yuck!) confirm. $\endgroup$ May 4, 2022 at 21:26
  • $\begingroup$ And human excrement too. Source: two toddlers and a poorly-trained puppy. $\endgroup$
    – Jim421616
    May 4, 2022 at 21:36
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The issue of hygiene that comes from having to put your mouth on everything you want to pick up.

I have two family members who face this ordeal on a daily basis: my baby kid and my dog. Hopefully at least one of them will grow over this issue over time.

In the meantime I have been reassured that things will be fine by the fact that kids and dogs have been doing this for millions of years and yet we still have humans and dogs alive today. Our pediatrician also told my spouse that our kid is protected by an immunological system[citation needed], so we only need to worry that he doesn't eat his own [redacted] nor come into contact with something he'd be allergic to.

I think the lesson here is that as long as your creatures have an immune system, they should be fine. Evolution will naturally select only those who are resistant to whatever germs are around, so they can lick the world in peace.

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Backwashing

Why not design your creature with a mouth that, unless in eating mode, is very good at keeping dirt near the outside?

Then rapidly shoot saliva globs out at high speed, cleansing the mouth.

Combine with a filter for maximum effectiveness; this is, after all, how industrial water filter systems work. Filter until the filter blocks, backwash, repeat.

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