This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

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n. An aquatic animal, such as a mollusk or crustacean, that has a shell or shell-like exoskeleton.

n. An aquatic invertebrate, such as a mollusc or crustacean, that has a shell.

n. Any aquatic animal whose external covering consists of a shell, either testaceous, as in oysters, clams, and other mollusks, or crustaceous, as in lobsters and crabs.

n. An aquatic animal, not a fish, having a shell, and especially one which comes under popular notice as used for food or for ornament.

n. A crustaceous animal, or crustacean, as a crab, lobster, shrimp, or prawn.

n. meat of edible aquatic invertebrate with a shell (especially a mollusk or crustacean)

n. invertebrate having a soft unsegmented body usually enclosed in a shell

"Domoic acid is produced by the diatom Nitzschia pungens and has been isolated in shellfish from Prince Edward Island, Canada. 10 This toxin is responsible for amnestic shellfish poisoning (ASP) in humans causing symptoms of gastroenteritis and neurotoxicity."

rock shell-fish   

shellfishes   

mollusk   

mussel    prawn    mollusk    squid    shrimp