FILARIA, in zoölogy, a genus of Entozoa, of the order Cœlelmintha, and family Nematoidea. The body is filiform, very long, and nearly uniform; head not distinct from the body; mouth round or triangular, naked or with papilæ; it is white, yellowish, or red. They are most commonly found in the abdominal cavity and between the peritoneal folds of mammalia and birds, in the air-cells of the latter. Species are also met with in reptiles, fishes, and insects. Filaria medinensis or guinea worm is common in hot climates.