Could a creature discard its skeletal system to function like an octopus?

Question

For a long time now I tried to make my creature work. Being from an alien planet, I wished it to be humanoid and capable of flight, while also making it able to slip into small crevices, however, as flight usually involve some kind of support system (be it an endo or exoskeleton), both traits seems essentially mutually exclusive. However, after observing the hospital monster in the 3rd season of the series Stranger Things, I started to wonder the possibility of a different approach(spoilers ahead).

the hospital monster

To put into context, the hospital monster is a creature made essentially of a conglomerate of cells and tissues of 2 humans, being capable to move like a vertebrate while also being able to squeeze through crevices much smaller than its size should allow. A specific behavior that called my attention about this being was how, while sliding though a sewer duct to escape, it left behind some bones which were too large for it to pass through. This last behavior showed it still had them to begin with, likely justifying its ability to move in a way much more similar to a vertebrate or arthropod than to a mollusk when the situation called for it.

Given this, I'd like to use a similar concept, with an omnivorous, human-sized humanoid creature having a more or less soft body and using certain hardened, bone-like structures to support itself (predominantly its limbs and parts of the chest, in an approximation of the ribs and sternum), but also being able to abandon said support structures, should it need to squeeze through tight spaces to escape, substituting them later. This however would, as far as I know, require a muscular system that can function like that of an octopus and like that of a vertebrate or arthropod depending on whether or not there's a skeletal system at the moment.

Leaving apart whether it could evolve naturally, Could such a concept of a creature which can discard its skeletal system (be it an endoskeleton or exoskeleton) in favor of the ability to squeeze into small crevices be implemented given our understanding of life and the laws of our universe?. While I'd also like to explore this concept regarding flight (although with a smaller creature), I'd prefer to focus on overall mobility on land in this question.

Answer 1

You can do it in reverse.

Your creature was basically amorphous. Then it developed the ability of gripping objects to manipulate them.

When humans grip some tool, the tool has a part that is enveloped by the human (the "handle"), and a different part that is the working bit. Initially, it was the same for the creature. It used sticks to pry prey from burrows without the need of exposing tender tendrils of itself to what, while prey, was still a potentially hungry and sharp-toothed critter. Once the prey had been skewered by a stick, the rest of the business went much better.

Then, like octopi do, the creature discovered how to fully envelope an object, using it as two connected "handles". This allowed the creature to e.g. raise a portion of itself much higher and faster than with any other means.

Raising a part of itself using a strong stick, a part that was further armed with more and more pointed sticks, might have enabled the creature to engage more interesting and tasty prey.

And after that, the creature developed locomotion. By gripping three or four sticks at the same time, and moving them rhythmically, the creature could walk and run way faster than it could slither before. It could conquer the solid ground instead of remaining near its home waters.

Finally, it developed the habit of keeping the bones of other creatures it ate, to use as an endoskeleton. But, while all the brouhaha of holding the bones and moving them has become autonomic, the creature has retained the ability of expelling those same bones at will (for example because they decay in time).

And so you have a creature that has a sort of endoskeleton, but can discard it at will.