Submarine starts to escape some shells (10)

I believe the answer is:

nautiluses

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'shells' is the definition.
The definition and answer can be both animals as well as being plural nouns.
Perhaps they are linked in a way I don't understand?

'submarine starts to escape some' is the wordplay.
'submarine' becomes 'nautilus' (submarine in 20,000 Leagues Under the Sea).
'starts to' suggests taking the first letters.
The initial letters of 'escape some' is 'es'.
'nautilus'+'es'='NAUTILUSES'

Can you help me to learn more?

I've seen this clue in the Sydney Morning Herald.

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