Broader term that includes crustaceans (crabs, shrimp) plus mollusks (clams, oysters). 'Shellfish' is more common in everyday cooking and eating contexts.
用法筆記
This word is most often used in the plural form (crustaceans) when referring to the group as a whole. The singular form 'crustacean' is used when talking about one individual animal.
常見錯誤
Crustaceans are a type of fish with scales.
Crustaceans are animals with hard outer shells, like crabs and lobsters.
Crustaceans are not fish; they belong to a different animal group (arthropods).
I ate a crustaceans for dinner.
I ate a crustacean for dinner.
When talking about one animal, use the singular 'crustacean' without the -s.