Cephalopods are strictly marine creatures, whose need to see through dark, murky water and blend in to colored choral beds is essential to their survival. Sharp eyes and the ability to change color helps.
The hypothalamus acts as the connector between the endocrine and nervous systems to achieve this.
Because it has to be that way
That isn't even possible. Your body is made of them. If you had none then you wouldn't be existing.
