How do sirenomelia and uromelia differ?

In the context of biological malformations, both sirenomelia and uromelia are conditions involving the fusion of the lower extremities, but they differ in the degree and nature of that fusion.

• Sirenomelia (also known as symmelus) is a severe abnormality where the legs are fused to a greater or lesser degree throughout their length, typically resulting in the absence of separate feet. This condition is often accompanied by the absence of anal and urinary orifices, as well as malformations of the genitals and parts of the intestinal and urinary tracts.12
• Uromelia (or uromelus) refers to a specific presentation of this sirenoid malformation characterized by the presence of a single, fused foot.2

Both conditions are rare developmental anomalies that have historically been associated with the mythical imagery of sirens or mermaids.2