You searched for: “cenadelphus
cenadelphus (s) (noun), cenadelphuses (pl)
Symmetrically conjoined twins: Cenadelphus refers to monozygotic twins (derived from a single fertilized egg zygote) ranging from two well-developed individuals joined by a superficial connection of varying extent, usually in the frontal, transverse, or sagittal body plane.

A "zygote" is a cell formed by the union of a male sex cell (sperm) and a female sex cell (ovum).