Tetrameridae is a family of spirurian nematodes. It is the smallest of the large genera making up the bulk of the superfamily Habronematoidea. Like all nematodes, they have neither a circulatory nor a respiratory system. They are parasites, chiefly of birds and cetaceans. This family contains the largest known nematode: Placentonema gigantissima is several meters long and has been found in the placenta of the Sperm Whale (Physeter catodon).