The most common and most likely answer to this crossword clue is the 9 letter word PARAMECIA
I've seen this crossword clue in The Guardian
P
A
R
A
M
E
C
I
A
Buddy explains!

The straight part
We know that "basic life form" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case basic life form = paramecia.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does PARAMECIA mean?
PARAMECIA noun- An oval-shaped protozoan organism of the genus Paramecium.