A person who would otherwise be a vegan makes the case that it is okay to eat non-sentient animals. She believes acerebral animals must be non-sentient: other authors have suggested that animals with distributed nodal nervous systems may be sentient.
http://sentientist.org/2013/05/20/the-ethical-case-for-eating-oysters-and-mussels/
I don’t have strong views on the topic.
My question is: Apart from bivalves, what animals have no brains?