pygoamorphus

Conjoined twins in which the parasite, attached to the buttocks of the autosite, is reduced to a formless mass or embryoma. See conjoined twins, under twin. [pygo- + G. a- priv. + morphe, form]

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py·go·amor·phus (pi″go-ə-morґfəs) asymmetrical conjoined twins in which the parasite is an amorphous mass attached to the sacral region of the more developed twin.