The idea of a group of explorers being absorbed, except their nervous systems, by an amoeba-like entity and then being able to exert control and eventually form bodily appendages sounds very much like "Four in One" (1953) by Damon Knight.
People are absorbed except for their nervous systems:
The fact remained that he—all that he could still call himself—was nothing more than a brain, a pair of eyes, a spinal cord, and a spray of neurons.
George Meister (our protagonist) initially has only limited control and can't coordinate with the others:
There were others, he knew, because occasionally he would feel a sudden acute pain down where his legs used to be, and at the same instant the motion of the landscape would stop with a jerk. That could only be some other brain, trapped like his, trying to move their common body in another direction.
But under pressure from predators, among other things, they learn to form appendages, initially simple legs, then more complex features like ears.
They do determine they must be hungry, but don't initially understand it because it's not a normal experience of hunger:
"We're hungry," George interrupted. "We didn't realize it, because we haven't got the organs that usually signal hunger. But the last thing this body ate was us, and that was a whole day ago. We've got to find something to ingest. And soon, I'd say."
Three others are ingested along with Meister; Vivian Bellis, who has some geological training, a military man Major Gumbs, and a Loyalty Monitor Miss McCarty. After they ingest sufficient mass, the blob fissions, leaving Gumbs together with Meister and Bellis together with McCarty. Each pair fight, Gumbs' attempt to crush Meister falling instead on himself and McCarty's attempt to kill Bellis causing the blob to eject her brain.
In the end they learn to make bodies, and look forward to living out from under the military-dominated society they came from:
"We'll never go back there, will we?" begged Vivian.
"No," said George confidently. "We'll let them find us. When they do, they'll be a lot more disconcerted than we will. We can make ourselves anything we want to be, remember."
[...] both of us will have super-intelligence. I don't see why not. We can direct our growth in any way we choose. We'll be more than human."
The story has been frequently anthologized, with 7 alone in the 1970s and 1980s. The most popular of these were probably The Great SF Stories 15 (Asimov, et al) and Robert Silverberg's Worlds of Wonder. It was first published in Galaxy, February 1953 and can be read at the Internet Archive.
