"Teratoma" is the term.... and it is technically classified as a very unique type of congenital defect. Some teratoma are malignant, and thus are considered "cancerous", though most are benign growths....
A teratoma could simply arise from a set of cells within a single organism that recieved the incorrect developmental messages- or could possibly be products from the merger of two sets of cells in an incomplete resorptive process. In this case, the first develops normally, and the second that does not fully resorb subsequently receives incorrect developmental messages (instead of undergoing apoptosis) that cause the formation of tissues (such as those you mention) in improper areas of the developing fetus.
You're absolutely correct- the causation is not fully understood. That's all "controversial" really means, "having different or opposing views", though we often ascribe an adversarial connotation to the word, there is no negativity inherent within the word itself .... Wisdom and new knowledge come from reconciling opposing or controversial viewpoints, and 'controversial ideas' are often sources that stimulate new inquiries, which lead us to greater understanding of the world and ourselves. As humans, we should strive to seek these out and inqure to resolve them. In the search for the solution, we will learn something that we did not know before, and may benefit from this knowledge.
The choice of term was used to correct a common misconception of chimerism- as the initial cells do not destroy (or consume) the secondary or merged cells- which is sometimes what happens in the case of twin resorption (vanishing twin). I did not use the technical term "resorb" or "resorption" because it's scientific jargon, and I try to avoid using specialized terms in posts, unless required based on context.
Adsorption was used in a previous post, which is also not the correct term- because this refers to particles "sticking to" or adhering to a solid surface or substrate, and forming a separate layer. Some examples of this would be like the particles in hard water depositing a separate layer of calcium on bath tile.... In this case, the calcium is still a separate layer, and does not become "part of" the bath tile. There is no evidence that the seconday or merged cells in this chimeric case formed a separate layer of mesoderm, endoderm, or ectoderm.... If the secondary cells had formed one layer of tissue during gastrulation, then the term Adsorption would be quite correct.
Absorbed isn't accurate, either- because this term used in a biological sense does refer to "the uptake of particles during digestion"- which as you and I (in different ways) have both stated- is not what occurred in this case. I did not use this term because most people think about something like paper towels "absorbing water" and I believed that use of this term would create improper confusion. E.G. "The primary blastula did not absorb the cells from the secondary blastula...." A reader might look at this statement and wonder, if these two things became one thing, why were they not in fact "absorbed"?
None of the above terms (Adsorption, Absorption or Resorption) accurately describes what happened in the case of this gestation and development. That's what made this case so unique, the cells merged into one structure, without destruction (resorption) of the secondary or merged cell line.
I have change the potentially perjorative word in my initial post (viz the section using the analogy involving inanimate balls of clay) to the word "destroy"... I hope that satisfies your previous objection to the word choice and further, clarifies why I selected the initial "common" term instead of the incorrect term "adsorb", the potentially confusing term "absorb", or the more technical but accurate term "resorb".
Thank you for your comment, and feedback. I appreciate your thoughtful analysis and note that all NFT corrections joyfully accepted in the spirit of cooperation. :)