[Grammar] Countable coral?

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“Coral are small animals that live in shallow sea water.”
This is a sentence from an English textbook. I always thought that the noun “coral” is uncountable. Is this a correct sentence?

 

[Tdol]

I'd use it uncountably if talking about a reef or the dried stony substance, but if you're talking about the organisms that make it, the plural makes sense to me.