Wiktionary
n. (context biology English) The fine, detailed structure of a biological specimen that can only be observed by electron microscopy
Wikipedia
Ultrastructure (or ultra-structure) is the nanostructure of a biological specimen, such as a cell, tissue, or organ, at scales smaller than can be viewed with light microscopy. It is viewed with ultramicroscopy or electron microscopy. Such cellular structures as organelles, which allow the cell to function properly within its specified environment, can be examined at the ultrastructural level.
Ultrastructure, along with molecular phylogeny, has often been a reliable (that is, phylogenetic) way of classifying organisms.
Usage examples of "ultrastructure".
The existence of identical macromolecules and immutable cellular ultrastructures, which had remained consistent throughout evolutionary history, could not be explained by the laws of classical chemistry.
One of the cases even had some electron micrographs taken, showing marked ultrastructure damage to nerve and muscle.
Us meat puppets are all too closely tied to our neural ultrastructure, but you've got a shitload of programmable gate arrays.
I can see ultrastructure, eyes zooming into coiled distance, the blue lucent flare of pseudocrystals refracting laser light.