The Spanish dancer, scientific name Hexabranchus sanguineus (literally meaning "blood-colored six-gills"), is a dorid nudibranch, a very large and colorful sea slug, a marine gastropod mollusk in the family Hexabranchidae.

[1]The taxonomy of the genus Hexabranchus has been controversial but a thorough molecular and morphological study published in 2023 showed that the name H. sanguineus was being used for at least 5 distinct species.

The pair of oral tentacles are constituted by a fine flexible membrane provided with large digital lobes.

[2] In a normal situation when the animal is crawling, the edges of its mantle are curled upwards creating a peripheral blister.

During daytime, the Spanish dancer hides away from the light in the crevices of its natural habitat to only come out late at night.