1.  shellfish(n = noun.food) - meat of edible aquatic invertebrate with a shell (especially a mollusk or crustacean);
is a kind of seafood
is a part of mollusc, mollusk, shellfish
has particulars: mussel, huitre, oyster, clam, cockle, crab, crabmeat, crawdad, crawfish, crayfish, ecrevisse, limpet, lobster, crayfish, langouste, rock lobster, spiny lobster, escallop, scallop, scollop

2.  shellfish(n = noun.animal) mollusc, mollusk - invertebrate having a soft unsegmented body usually enclosed in a shell;
is a kind of invertebrate
has parts: carapace, cuticle, shell, shield, shellfish
is a member of mollusca, phylum mollusca
has particulars: scaphopod, gastropod, univalve, chiton, coat-of-mail shell, polyplacophore, sea cradle, bivalve, lamellibranch, pelecypod, cephalopod, cephalopod mollusk

   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. [1913 Webster]

shellfish, n.
1 an aquatic shelled mollusc, e.g. an oyster, winkle, etc.
2 a crustacean, e.g. a crab, shrimp, etc.

N  animal, animal kingdom, fauna, brute creation, beast, brute, creature, critter, wight, created being, creeping thing, living thing, dumb animal, dumb creature, zoophyte, mammal, bird, reptile, amphibian, fish, crustacean, shellfish, mollusk, worm, insect, arthropod, microbe, microbe, animalcule, alligator, crocodile, saurian, dinosaur (extinct), snake, serpent, viper, eft, asp, aspick, frog, toad, trout, bass, tuna, muskelunge, sailfish, sardine, mackerel, ant, mosquito, bee, honeybee, tardigrade, spider, biped, quadruped, webfoot, flocks and herds, live stock, domestic animals, wild animals, game, ferae naturae, beasts of the field, fowls of the air, denizens of the sea, black game, black grouse, blackcock, duck, grouse, plover, rail, snipe, horse, cattle, kine, ox, bull, bullock, cow, milch cow, calf, heifer, shorthorn, sheep, lamb, lambkin, ewe, ram, tup, pig, swine, boar, hog, sow, steer, stot, tag, teg, bison, buffalo, yak, zebu, dog, cat, dog, hound, pup, puppy, whelp, cur, mongrel, house dog, watch dog, sheep dog, shepherd's dog, sporting dog, fancy dog, lap dog, toy dog, bull dog, badger dog, mastiff, blood hound, grey hound, stag hound, deer hound, fox hound, otter hound, harrier, beagle, spaniel, pointer, setter, retriever, Newfoundland, water dog, water spaniel, pug, poodle, turnspit, terrier, fox terrier, Skye terrier, Dandie Dinmont, collie, feline, puss, pussy, grimalkin, gib cat, tom cat, fox, Reynard, vixen, stag, deer, hart, buck, doe, roe, caribou, coyote, elk, moose, musk ox, sambar, bird, poultry, fowl, cock, hen, chicken, chanticleer, partlet, rooster, dunghill cock, barn door fowl, feathered tribes, feathered songster, singing bird, dicky bird, canary, warbler, finch, aberdevine, cushat, cygnet, ringdove, siskin, swan, wood pigeon, vermin, varmint, pest, animal, zoological equine, bovine, vaccine, canine, feline, fishy, piscatory, piscatorial, molluscous, vermicular, gallinaceous, rasorial, solidungulate, soliped.