### Clue: Ancient sea-creatures with shells, say, paladins picked up (9)
### Answer: AMMONITES 
 ### Explanation: Definition: Ancient sea-creatures
 AMMO(short for "ammunition", which includes/say, "shells"/explosive projectiles or bombs) + **homophone of**(… picked) "knights"(paladins/heroic champions of noble causes).
… and the inside of one: