Linked from
The 7 pages that link to Shellfish, each with the reason it gives.
FishCompared with: Shellfish are seafood, but they are not vertebrate fish.
Crab meatNarrower topic: Crab meat belongs to the edible crustacean branch of shellfish.
Animal shellRelated: Harvested shellfish connect shell-bearing animals with food and fisheries.
Calcium cycleBroader topic: Their remains carry calcium from living biomass into sediments.