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What invertebrate is the simplest organism with a brain?

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May 14, 2012 9:33AM

I believe the Geonemertine worms produced the earliest brain. Earlier organisms such as the flatworms have extensive nervous systems, (such as light detection, and sensing systems), but the brain had to await the arrival of a blood supply.

This is a debated question and depends upon your definition of a brain.

If mere reflex activity (i.e. non - purposive) then the flatworms take the palm.

If metabolic purposive activity is your criteria, then the Geonemertine are your boys. This requires a blood supply, which arrives simultaneously with the arrival of a brain. But the heart had to wait further development. And the use of a blood supply infers that cerebration may take place independent of stimuli. [Not that they are solving Rubik Cubes!]