[randcraw]

I think every animal from arthropods (~bugs) upward in terms of complexity have connected nervous systems with bilateral symmetry. But many simple invertebrates don't, like jellyfish.

But the mere presence of bilateral interconnectedness doesn't mean that their 'brain' conveys much information or coordinates much activity in those linnaean classess. In all invertebrates, most(?) nervous control arises locally, via clumps of neurons (ganglia). The lower the class, the larger the fraction of control arising locally from ganglia. For example, earthworms have only ganglia (IIRC).