Initially, all molluscs made ornate shells, say (4)
I believe the answer is:
ammo
'shells say' is the definition.
'ammo' can be an answer for 'shells' (I've seen this in another clue). I am unsure of the 'say' bit.
'initially all molluscs made ornate' is the wordplay.
'initially' indicates taking the first letters.
The initial letters of 'all molluscs made ornate' is 'AMMO'.
Can you help me to learn more?
(Other definitions for ammo that I've seen before include "round" , "Contents of magazine" , "What's fired from a gun (abbr)" , "Slugs perhaps" , "essential supplies for soldiers" .)