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Crabby types, drunkenly egocentric in speech (9)

Ross

I believe the answer is:

shellfish

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'speech' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.

I cannot understand how the rest of the clue works.

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(Other definitions for shellfish that I've seen before include "Category of seafood" , "Lobsters, cockles, mussels etc" , "Oysters, cockles, mussels etc" , "Crustaceans" , "A shrimp, maybe" .)

I've seen this clue in The Times.
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