The most common and most likely answer to this crossword clue is the 9 letter word ARTHROPOD
I've seen this crossword clue in The Times
A
R
T
H
R
O
P
O
D
More clues leading to the result ARTHROPOD
- Devious trap-door hides head of hairy spider, say
- A tick for one old king skipping posh old school
- Legendary ruler giving away universal ring case for scarab, say
- Trap door collapsed trapping hard crustacean?
- Creature with shell, or hard top, alternatively
- Possibly fly east from land getting work in bar
- Horse bitten by variety of trapdoor spider, maybe
- Non-university man: old-school worker for instance?
- Invertebrate rook oddly found in new hardtop
- One has hard cover or hard top, possibly
Buddy explains!

The straight part
We know that "spider, say" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case spider, say = arthropod.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 ARTHROPOD mean?
ARTHROPOD noun- An invertebrate animal of the phylum Arthropoda, characterized by a chitinous exoskeleton and multiple jointed appendages