Molluscs are a group of invertebrates which include oysters, abalone, snails and squid. Note in Europe that molluscs and crustaceans are considered to be 2 separate food groups whose allergens need to be declared in packaged food. In the US these are both grouped under the term 'shellfish'.
The WHO allergen index covers 6 species of molluscs linked to allergic reactions.
The main allergen in all 6 species is Tropomyosin, which is a protein found in the exoskeletons of the animals.
Allergy to molluscs has not been linked to any syndromes
Molluscs allergy is linked to crustacean allergy; lobster, prawn, scampi, crab and shrimp all contain the main allergen - tropomyosin.
Catfish, some types of salmon and tilapia are types of fish which have also been identified as containing the allergen tropomyosin, there may be cross reactivity between eating certain types of fish and molluscs.
There is a lot of research into a link between dust mite allergy and molluscs allergy, this is again attributed to the common allergen - tropomyosin.
Effect of Heat Processing on IgE Reactivity and Cross-Reactivity of Tropomyosin and Other Allergens of Asia-Pacific Mollusc Species: Identification of Novel Sydney Rock Oyster Tropomyosin Sac g 1, 2018