In Gulf earlier, Scotsman's finding old Red Sea denizens (11)

I believe the answer is:

abyssinians

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'old red sea denizens' is the definition.
Although both the answer and definition are plural nouns, I cannot see how they can define each other.

'in gulf earlier scotsman's' is the wordplay.
'gulf' becomes 'abyss' (I've seen this before).
'earlier' means one lot of letters go next to another.
'scotsman's' becomes 'ian's' (common Scottish name).
'in' after 'abyss' is 'abyssin'.
'abyssin'+'ians'='ABYSSINIANS'

'finding' acts as a link.

Can you help me to learn more?

I've seen this clue in The Everyman puzzle in The Observer.

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