Spiders have donut shaped brains. Source: owned a tarantula. Some animals jon't have bilaterally symmetric brains on account of having brains, like jelly fish.
Nah, I just became fascinated with them while I had one. Not that I'm above dissection, but when he died, it smelled pretty bad. I wasn't about to keep that thing lying around.
I remember an article saying that esp. in smaller spiders (so probably not tarantulas) the "brain" doesn't really have a simple shape, extending even into the limbs.
That's also true for tarantulas. Their nervous system is fairly decentralized, but there's still a noticeable mass in their heads which is oddly shaped.