The Blue Velvet Nudibranch, also known as the Head Shield Sea Slug, is black in color with blue lines around the outside of its body and down the middle of its head. It has a hammer shaped head and two appendages at the rear, mimicking a flatworm.

This specialized eater will consume flatworms in the aquarium. It sucks up the flatworms using a tube like proboscis and makes a great natural alternative for flatworm control. However, it must be provided with a steady diet of flatworms in order to thrive. In addition, it is sensitive to rapid changes in water conditions and does not have a long life expectancy. Because of this, only expert aquarists should attempt to maintain this species.