parabiosis

noun

1. 1.The (natural or surgical) union of parts of two organisms, especially in such a way as to cause them to share their vascular systems. Organisms so joined then are called parabionts.
2. 2.The fusion of two embryos to form conjoined twins
3. 3.A transient physiological state of suspension of obvious vital activities such as to enable an organism to escape the notice of its enemies or to conserve its energy.
4. 4.A form of symbiosis, typically among ants, in which different species share common nest galleries but maintain distinct broods and do not practice mutualism other than incidentally.
5. 5.An alien form of life within an organism, commonly invasive, such as a growing cancer.