SHELLFISH
mollusk, mollusc, shellfish
(noun) invertebrate having a soft unsegmented body usually enclosed in a shell
shellfish
(noun) meat of edible aquatic invertebrate with a shell (especially a mollusk or crustacean)
Source: WordNet® 3.1
Etymology
Noun
shellfish (countable and uncountable, plural shellfish or shellfishes)
An aquatic invertebrate having a shell, such as a mollusc or crustacean, especially when edible.
Source: Wiktionary
Shell"fish`, n. (Zoöl.)
Definition: 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.
Source: Webster’s Unabridged Dictionary 1913 Edition