The most common and most likely answer to this crossword clue is the 9 letter word ENDODERMS
I've seen this crossword clue in Financial Times
E
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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.
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Crossword Answer definitions
ENDODERMS noun- One of the three tissue layers in the embryo of a metazoan animal. Through development, it will produce the digestive system of the adult.