Question: The food group Shellfish includes what varieties of food?
About the article "Seafood", section "Abstract".

Candidate passages:
Shellfish is a culinary and fisheries term for exoskeleton-bearing aquatic invertebrates used as food, including various species of molluscs, crustaceans, and echinoderms.
Although most kinds of shellfish are harvested from saltwater environments, some kinds are found only in freshwater.
In addition a few species of land crabs are eaten, for example "Cardisoma guanhumi" in the Caribbean.
Despite the name, shellfish are not a kind of fish, but are simply water-dwelling animals.
Many varieties of shellfish (crustaceans in particular) are actually closely related to insects and arachnids, making up one of the main classes of the phylum Arthropoda.
Cephalopods (squid, octopus, cuttlefish) and bivalves (clams, oysters) are molluscs, as are snails and slugs.
Familiar marine molluscs enjoyed as a food source by humans include many species of clams, mussels, oysters, winkles, and scallops.
Some crustaceans commonly eaten are shrimp, lobster, crayfish, and crabs.
Echinoderms are not as frequently harvested for food as molluscs and crustaceans, however sea urchin roe is quite popular in many parts of the world.
Most shellfish eat a diet composed primarily of phytoplankton and zooplankton.
Shellfish are among the most common food allergens. 
Langoustines or Norway lobsters – "Nephrops norvegicus" – are roughly the size of a large crayfish and fished from silty bottom regions of the open Atlantic Ocean, and parts of the Mediterranean.
The fleshy tail of the Norway lobster is closer in both taste and texture to lobster and crayfish rather than prawn or shrimp.
They are often informally known as Dublin Bay prawns, though the term "prawn" can be confusing since it is sometimes used to describe several varieties of shellfish: the first group includes members of the lobster family such as scampi ("langoustine" in French and "cigala" in Spanish), while the second takes in large shrimp, particularly those that live in fresh water.
However, in terms of biological classification, lobsters like scampi are of a different family from prawns/shrimp.
The name is used loosely both in Italy and elsewhere to refer to other similar species, though some food labelling laws (in Britain, for example) define "scampi" as "Nephrops norvegicus". 
Fish is consumed as a food by many species, including humans.
The word "fish" refers to both the animal and to the food prepared from it.
In culinary and fishery contexts, the term fish also includes shellfish, such as molluscs, crustaceans and echinoderms.
Fish has been an important source of protein for humans throughout recorded history. 
This is a list of notable fish dishes.
The word "fish" refers to both the animal and to the food prepared from it.
In culinary and fishery contexts, the term fish also includes shellfish, such as molluscs, crustaceans and echinoderms.
Fish has been an important source of protein for humans throughout recorded history. 
The term "environmental toxin" can sometimes explicitly include synthetic contaminants such as industrial pollutants and other artificially made toxic substances.
As this contradicts most formal definitions of the term "toxin", it is important to confirm what the researcher means when encountering the term outside of microbiological contexts.
Environmental toxins from food chains that may be dangerous to human health include:  Paralytic shellfish poisoning (PSP)  Amnesic shellfish poisoning (ASP)  Diarrheal shellfish poisoning (DSP)  Neurotoxic shellfish poisoning (NSP)