It is more probable that the third one has a more developed sense of the vision with a large eye, and its movements. Also with a opened back to receive its nutrition and optic nerve.
Sources:
Zihlman, Adrienne. (2006). «The Ape in the Tree». International Journal of Primatology (en inglés) 27 (4): 1227-1228
Cell shape is related to its function. It can be justified by citing examples of nerve cell which is long and it helps it to carry information from one part of the body to another. White blood cells and Amoeba do not have a definitive shape; their cells have the ability to change their shape.