The sciapod is a small humanoid creature, which is distinguished by a single large leg. This leg would be like a single leg, without duplicate structures. It would also be symmetrical. They move by jumping around, and are quite quick. The leg would be roughly as flexible as a human leg
While sirenomelia and such things can cause the legs to fuse, this wouldn't work for the sciapods; because of their powerful leaps, they need a solid pelvis (or other such joint), which is not found with sirenomelia
How would such a being fit together internally?