Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a novel human coronavirus and the causative agent of coronavirus disease 2019 (Covid-19). There is an urgent need for effective antivirals to treat current Covid-19 cases and protect those unable to be vaccinated against SARS-CoV-2. Marine molluscs live in an environment containing high virus densities (>107 virus particles per ml), and there are an estimated 100,000 species in the phylum Mollusca, demonstrating the success of their innate immune system. Mollusc-derived antivirals are yet to be used clinically despite the activity of many extracts, including against human viruses, being demonstrated in vitro. Hemolymph of the Pacific oyster (Crassostrea gigas) has in vitro antiviral activity against herpes simplex virus and human adenovirus, while antiviral action against SARS-CoV-2 has been proposed by in silico studies. Such evidence suggests that molluscs, and in particular C. gigas hemolymph, may represent a source of antivirals for human coronaviruses.