Relevant to the thing this question is trying to get at: my impression is that our c. elegans models are dramatically better than mouse/human models. Like, I just googled it real quick, and found that an adult c. elegans has 302 neurons and 56 glial cells. I’m pretty sure those are not population averages; those are exact numbers in normal adult c. elegans. I think I’ve even heard that we have a decent idea of what each of those neurons does?
C. elegans indeed has a fixed number of neurons (and other cells) and that’s partly the reason why it gets used as model organism.
There’s the OpenWorm project (googling also finds WormSim) that tries to model C. elegans whole neurology. From what I heard from people with domain expertise the model isn’t good enough for us to say that we truly understand everything.
Ooh, that’s a good creature to look at. Thanks!