The Spanish dancer is typically red (indicated by its species name, sanguineus) and sometimes yellow and it is one of the largest nudibranchs, many over 40 cm in length.
These brightly colored, undulating swimmers are found throughout the tropical Indo-Pacific and Red Sea. They were given the name Spanish dancer because their swimming movement (often referred to as dancing) resembles the movement of a Spanish flamenco dancer’s dress. The animal whirls, spins, and undulates; its unfurled parapodia (the wide edges of the mantle) create the ruffled-dress look that propels it though the water.
When the Spanish dancer is not dancing, it crawls. It’s parapodia are tightly curled around the edges of the mantle, and it moves quite slowly.
As an unusual member of the superfamily Eudoridoideahe, the feather-like or soft, leaf-like gills on the mantle are exposed and do not have a pouch in which they can retract. In fact, each gill is inserted separately into the body wall.