The most common and most likely answer to this crossword clue is the 11 letter word OPISTHOSOMA
O
P
I
S
T
H
O
S
O
M
A
Buddy explains!
The straight part
We know that "spider’s abdomen" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case spider’s abdomen = opisthosoma.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 OPISTHOSOMA mean?
OPISTHOSOMA noun- The posterior abdomen of the chelicerates