The parapodia (fleshy winglike outgrowths) of Notarchus are almost completely fused, forming the parapodial cavity.
Life habits
These sea hares are able to swim by jet propulsion, through sucking in water through the small anterior opening of the parapodial cavity and then squirting water from the back of it. While doing so, they tumble and make a series of backward somersaults. In this unusual manner, they move quickly out of harm's way over short distances.