I think the closest thing would be acardiac acephalus, which is like, just a blob of baby flesh with legs sticking out the bottom:
Another gross thing to see along these lines. Not a parasitic twin as they are attached on the outside. But are extremely rare cases of fetus in fetu, where the partial and really fucked up pieces, or formations, not sure how to describe it best, blobs with some recognizable deformed body parts, and can range to some that appear as almost nearly fully formed that stopped developing at some point, can be pretty horrifying. They are basically a parasitic twin but develop inside the infant who can be term, alive and healthy. And they leech off the babies blood supply where they attach to, usually the abdomen. There are tumors called teratomas that can have hair and teeth and are gnarly too, so they really have to have an expert to determine which, the tumors are not as rare as the fetus in situ.
I watched some documentary about a child in a third world country that had a huge abdomen, don't remember his age but he was walking and talking, the kid looked pregnant and about to burst. When finally taken to hospital and they did surgery, they removed a large, horrifying thing that was believed to be a situ situation., there was hair, and parts that looked like a partial deformed foot, and weird configurations.
They shamed the mother so badly that she would not come back to the hospital to view this horror. The attitude was along the lines of this abomination came from you, suffer and see what you made. It was awful, and she did relent and visit as they showed her this thing.
Other countries don't give you hand outs and ass pats for delivering kids like the ones in this thread, quite the opposite. Keeping them alive is not even a consideration, and the mother are often shamed and abandoned by the husband and family.
The good part was the boy recovered from the surgery and was doing well health wise.
Edit, words hard after 12 hour shift.