Myri
Alien species description
Their vaguely humanoid-shaped bodies' surfaces are porous, peppered with large holes, to the extent that there's about 1/4 to 1/3 of their outsides that isn't technically 'surface' but empty space leading in. The cavities interconnect inside in a labyrinthine network. The structure of their limbs, head and torso looks less like bones than like some kind of outer cartilaginous scaffolding, the rough blueprints around where bodies 'should' be.
Little creatures, that kind of look like insects and fly, crawl, climb, scuttle, dig or swim, go in and out of them several times every day. They're not quite hollow, but there's enough room in them for a creature to go into an elbow hole and later come out of a knee hole or go into a torso hole and later come out of a hole where an eye socket would be, if they had eyes to see with. When the creatures settle in them, there are protrusions and cavities for them to fit in, shaped in specific patterns.
Every creature carries inside it one of many kinds of 'filling': Some have a set of skills, some have a memory of a place, activity or experience, some have knowledge related to one field, some have emotions, feelings or opinions. If a creature carrying the experience of having been in a specific area flies out of a Myri's hand, it not only forgets how the area was laid out so that it couldn't find its way around in it anymore, but it forgets even having been there at all.
However, if a Myri who's never defused a bomb is near a bomb threat, and a creature holding a bomb-defusing expertise 'filling' crawls into its foot, it'll be able to defuse it as well as if it'd been defusing bombs all its life. Myri can actually 'pass on' an experience, and have a fluid concept of identity based on the fact that they're being taken apart and being put back together by other Myri, as well as taking and putting together other Myri every day. Parts of them die and are reborn often, and attachment to specific ones fluctuate based partly on which other parts are in them at the time.
One way of classifying creature 'fillings' is in the 4 categories: some that Myri want to give away and that other Myri want to receive, some that Myri want to keep and that other Myri don't want to receive, some that Myri want to get rid of and that other Myri don't want to receive, and some that Myri want to keep but that other Myri want to receive, possibly in exchange for another particular one. Of course, one Myri won't always want to keep or give away the same types as another given Myri might. Some types of 'fillings' are very rare and others are very common, and they shape not only the Myri's socioeconomic reality and interdependent community but their whole sense of their identities and continuation.
If some of them disappeared some of their specific 'fillings' couldn't be recovered. At the same time, if an experience you shared with a Myri gets transferred into another one and the first one is lost, it opens the question of just what was lost by it. The Myri are in a sense 'modular', their structure itself is unique but what they remember as their experiences didn't originally belong to them and it can always be lost later.
Some consider the Myri to be immortal 'in pieces', some consider that they die and are reborn every day. Sometimes creatures will get out of a Myri even though it's trying to keep them in, stay in even though it's trying to let them out, stay out even though it's trying to let them in, or sometimes they'll get into one even though it's trying to keep them out. This is rare enough to be considered a disease when it does, and if it starts happening often it can either mean that there's something wrong with the creature, or that it's its Myri 'frame' itself which is breaking down.
A few creatures carry the belief, despite what the other assemblies of them in Myri, as Myri, are conscious of, that the frames absorb subconscious memories of how different combinations of creatures affected them as they went through them over the years - memories that disappear when the frames break. But most Myri try not to let those creatures in.