Thelaziidae is a family of spirurian nematodes, which form the mid-sized lineage of the superfamily Thelazioidea. Like all nematodes, they have neither a circulatory nor a respiratory system.
They number 7 genera or so, with a few dozen species all together. Mostly parasites of birds, a few have also been found in other vertebrates.
The subfamily Oxyspirurinae is monotypic, as are several little-known genera in the Thelaziinae; these all might not be valid. All together, the systematic layout of this family is liable to change and cannot be considered more than tentative.
Subfamily Oxyspirurinae <small>Skrjabin, 1916</small>
Subfamily Thelaziinae <small>Skrjabin, 1915</small>