Drosophila connectome by Ciro Santilli 32 Updated Created
As of 2022, it had been almost fully decoded by post mortem connectome extraction with microtome!!! 135k neurons.
That article mentions the humongous paper elifesciences.org/articles/66039 elifesciences.org/articles/66039 "A connectome of the Drosophila central complex reveals network motifs suitable for flexible navigation and context-dependent action selection" by a group from Janelia Research Campus. THe paper is so large that it makes eLife hang.