Final answer:
The ability of separated embryonic cells to individually develop into complete adult animals indicates they are totipotent. These cells undergo cellular differentiation to form all types of tissues and organs required for a functioning adult organism, which is a key feature of the early development stages.
Step-by-step explanation:
When observing the phenomenon where each of the eight separated cells from an embryo develops into a complete adult, this suggests that the animal in question has totipotent cells during the early stages of embryonic development. Totipotency is the ability of a single cell to divide and produce all of the differentiated cells in an organism, including extraembryonic tissues. In the process of animal development, these totipotent cells undergo cellular differentiation, which is the process by which a less specialized cell becomes a more specialized cell type, and this specialization is key to forming different tissues and organs.
During the early stages of development, the single-celled zygote undergoes cleavage, forming smaller cells known as blastomeres without increasing the overall size of the embryo. Eventually, these cells specialize to form the various tissues and organs necessary for a fully functional adult organism by the process of differentiation. This ability to regenerate whole individuals from isolated embryonic cells is a remarkable feature of early developmental stages not found in all animal groups.