If I recall my invertebrate zoology correctly, multible animal hosts
are common with parasites and other invertebrates. You are right that
these little animals can be soo amazing that they seem almost alien.
In fact, the first Alien movie did a relatively good job of showing
the life cycle of an overgrown invertebrate that you might find on
earth (even its proboscis)!
The other thing you describe sounds something like slime mold which
I remember being totally facinated with in botany. It seems like something
between plant and animal.
Check out a good zoology textbook. Hickman et al., "Integrated
Principles of Zoology" was a good one but I'm not sure what is best now.
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Donald Doherty
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