It's actually a 'sea hare'. It is a harmless herbavore. You see them a lot in Spring in the grassbeds of the bay area and less frequently in the Gulf. They get big- seen em' bout 10" before. They glide through the water with an undulating patern, similarly to a cuttlefish. Occassionally divers will find 2-3" bright colored ones on the reef and some wrecks around here. They call them 'spanish dancers' as a reflection of their colors and 'dancing' like apearance in the water. Neat find.