In the order Tylenchida a differentiation is made between the primitiv
e head and the nonprimitive head. Primitive heads are found in all sub
orders, e.g. in the Tylenchoidea (suborder Tylenchina) primitive heads
are present in the Anguinidae. In the other families of the Tylenchoi
dea definite patterns are found that help to characterize the several
families. A lateral elongation of the pattern is found in the Tylenchi
dae and the Belonolaimidae; a dorso-ventral elongation in the Pratylen
chidae. The subfamily Meloidogyninae has the same head end-on view as
the Pratylenchidae and the subfamily Heteroderinae has the same head a
s the family Hoplolaimidae.