The
order Ascaridida includes several families of
parasitic roundworms with three "lips" on the anterior end. They were formerly placed in the
subclass Rhabditia by some, but morphological and
DNA sequence data rather unequivocally assign them to the
Spiruria. The
Oxyurida and Rhigonematida are occasionally placed in the Ascaridida as
superfamily Oxyuroidea, but while they seem indeed to be Spiruria, they are not as close to
Ascaris as such a treatment would place them.