sirenomelia sympodia (one fused foot)
In sympus dipus (symmelia), both the feet are seen separately. In sympus monopus (uromelia), a single foot is present. In sympus apus (sirenomelia,) the foot is absent
Discussion
"Symelia" is the fusion of the lower extremities,2 and it has been classified into three types: 1) Apus- no feet, only one tibia and one femur, 2) Unipus- one foot, two femora, two tibiae, two fibulae, and 3) Dipus- two feet and two fused legs (giving the appearance of a flipper).
Symmelia is basically classified according to the number of feet present. Tripodial symmelia contains three feet, dipodal symmelia have two feet, monopodal symmelia consist of one foot and apodal symmelia or sirenomelia which contain no feet and more severe form and closely related to a mermaid.