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There is a creature. Let's call it a Blop.

Blops are fairly simple creatures: They consist of a tough, flexible outer skin and then an inner structure that is (essentially) organs and tentacles floating in goo. This gives them a remarkable versatility, as they can literally flip end-to-end within their own skin, or push their organs through a small space one at a time while remaining safely intact. They can best be thought of as the unholy offspring of an octopus and a honey badger.

Respiration is fairly simple: Blops are amphibious swamp dwellers, so a semi-permeable skin allows them to breathe and exhale simultaneously. The issue that I'm having with the Blops is that they are relatively high-energy creatures (they burn a lot of calories), and so have to actively consume other carbon based material in order to survive (Don't worry too much about what they're eating. If you're assuming a certain kind of biomass just note it in the answer)

Given that the Blops have an outer skin with no orifices and can be at any orientation within said skin, how can they eat and defecate?

One last thing: Ideally a Blop should be able to eat while on a person's shoulder (I'm not planning any space piracy. No sir! Not me!), but it isn't required.

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    $\begingroup$ "Burn a lot of calories" = "use a lot of oxygen" I think the square-cube law is going to make any reasonably sized Blop unable to absorb enough oxygen with the naive semi-permeable skin approach. Depending on how hand-wavy you want to be, you may want to think more about breathing. $\endgroup$ – R.M. Jan 13 '16 at 17:38
  • $\begingroup$ @R.M. : This is one of the joys of the Blop. The actual mass of creature inside the goo-filled skin ball is much lower than the amount of skin would suggest. That and I planned on an awful lot of anaerobic respiration taking place. It is a swamp dweller after all! $\endgroup$ – Joe Bloggs Jan 13 '16 at 20:00
  • $\begingroup$ Where can I buy a Blop? I do, in fact, have free space on my shoulder. $\endgroup$ – BrettFromLA Jan 13 '16 at 23:25
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As an alternative to the amoeba model, you might consider a fungus-style digestive system. This would allow it to munch on items larger than itself, since it lacks a mouth with which to take bites.

The blop swims next to some foodstuff. Over the course of the next few minutes, its surface extrudes some small-diameter hollow fibres (like fast-growing mycelial cords) into its intended meal. The growth of these fibres occurs at the tips, and releases digestive enzymes as a by-product, so the tip is always immersed in a pocket of enzymes and partially digested food matter. The fibres conduct the mixture back to the blop, where it mixes with the goo (which I infer is meant to perform the role of circulatory system). One of its internal organs is a kidney-equivalent, which processes the components that aren't metabolically useful and converts them into something that can diffuse out of the blop's skin.

If the blop finishes its meal, or is threatened by a predator, it causes the fibres to break away from its skin by chemical signals or nerve impulses or what have you, but the little pores where the fibres were attached heal rapidly. This would mean it prefers to eat big meals (like animals that have drowned in the swamp) and remain undisturbed while it eats, because each meal incurs some energy cost to grow the tendrils, and it has to provide enough nutrition to offset that.

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  • $\begingroup$ This.. makes perfect sense for a swamp dweller. +1! $\endgroup$ – Joe Bloggs Jan 14 '16 at 9:24
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Like an amoeba.

Have the Blop envelope what it wants to eat in a subsection of its outer membrane called a vacuole. It can then fill it with acid/digestive enzymes. It can also dispose of waste in a similar fashion, by reconnecting the vacuole to the outside.

In essence anything the Blop eats gets its own private stomach that would be 'floating' in the goo with the main organs.

Edit

In light of additional information, the Blop will have to simply envelope its food, excreting acids and digestive enzymes into the food-filled envelope and reabsorbing the dissolved nutrients through its semi-permeable skin. This process will limit the waste generated by the Blop as the semi-permeable skin will only permit useful particles through and afterwards the undigested material will simply be released.

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  • $\begingroup$ The skin is a single solid outer piece, sadly, so deconnecting and reconnecting the vacuole wouldn't work (should have made that more explicit in the question, sorry!). Engulfing and then holding the opening tightly closed would though. $\endgroup$ – Joe Bloggs Jan 13 '16 at 14:04
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The process you're searching for is exactly how starfish eats : they "vomit" their stomach to have it attacks the inner organs of the seashell they're trying to eat. As wikipedia says ...

the cardiac stomach can be everted from the organism's body to engulf and digest food. When the prey is a clam or other bivalve, the starfish pulls with its tube feet to separate the two valves slightly, and inserts a small section of its stomach, which releases enzymes to digest the prey. The stomach and the partially digested prey are later retracted into the disc. Here the food is passed on to the pyloric stomach, which always remains inside the disc. The retraction and contraction of the cardiac stomach is activated by a neuropeptide known as NGFFYamide.

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    $\begingroup$ How does this solve the problem of having skin with no orifices? $\endgroup$ – wizzwizz4 Jan 13 '16 at 19:37
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In a way, your Blops already have orifices, because they have "a semi-permeable skin [that] allows them to breathe and exhale simultaneously"

The simplest way not to make those orifices any larger is to allow some liquid, such as water, to enter and leave, absorbing some minerals along with it.

Perhaps your Blops are green, and filled with chlorophyll, which energizes it just like a plant: using water, some trace minerals, breathed in CO2, and sunlight?

Note that this (probably doesn't) satisfy everything a "high energy creature" needs. High energy animals such as small birds can succeed because they are constantly eating insects, worms, etc. The blop, without an opening large enough to constantly eat high-density carbs, is at odds with its "high energy" requirement - unless it is eating massive amounts of tiny lifeforms (example: Blue Whale) while it constantly absorbs and releases water.

"It's absorbing carbon, but it's not growing!" - perhaps the carbon (and other waste materials) goes into the making of its skin, which it sheds often. It might be a bit smelly if its just had a big meal and shed..

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