the following is an excerpt from the book ‘play’ by dr. stuart brown: 

the juvenile sea squirt has a primitive spinal cord and a bundle of ganglia that act as a basic brain. this tiny brain helps it move selectively toward nutrients and away from harm.

like most oceanic creatures, the juvenile sea squirt spends his days exploring the sea and growing. once the sea squirt comes to adulthood, it attaches itself permanently to a rock, a boat's hull or pilings. it no longer needs to monitor the world as it did as a juvenile, because the passing current provides enough nutrients for the sea squirt to survive. 

it's life becomes purely passive. the adult sea squirt becomes the couch potato of the sea.

in a surprisingly macabre twist, the sea squirt digests its own brain. without the need to explore for sustenance, the creature devours its own cerebral ganglia. it’s like something out of a stephen king book - 'all work and no play make the sea squirt a brain eating zombie'