Mammals stamp on particles (3,5)

I believe the answer is:

sea lions

'mammals' is the definition.
(sea lion is a kind of mammal)

'stamp on particles' is the wordplay.
'stamp' becomes 'seal' (seal is a kind of stamp).
'on' is a charade indicator (letters next to each other).
'particles' becomes 'ions' (electrically charged particles).
'seal'+'ions'='SEA-LIONS'

(Another definition for sea lions that I've seen is " Marine creatures".)

I've seen this clue in The Guardian.

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