Reaching sizes of at least 16 inches (40 cm), the Spanish dancer is the largest nudibranch and one of the largest sea slugs on the planet. Like most nudibranchs, the Spanish dancer is brightly colored and does not blend in well with its surroundings. This bright coloration, similar to that of the poison dart frogs and many other species, serves as a warning to potential predators that the Spanish dancer does not taste good and may even make a predator sick.
Though this species spends most of its time crawling along the reef surface, it will swim when threatened, violently flapping its external gills and other appendages and displaying its brightest warning colors. This behavior reminded some observers of a flamenco dancer, earning the Spanish dancer its common name.
Spanish dancers are specialized predators that prefer to eat sponges and concentrate compounds found in their prey to provide their own chemical defense and defense for their eggs. Like other nudibranchs, Spanish dancers are simultaneous hermaphrodites; all individuals are both male and female. Individuals cannot self fertilize, however, and they always require a mate. Once eggs are deposited on the reef surface, neither parent provides care. The eggs do contain a dose of the defense chemicals that the adults use to ward of predation, and they are brightly colored, an attempt to warn potential egg predators of this defense.
Population trends in Spanish dancers are not currently known, but there is no evidence to suggest that human activities threaten this species. It is important for scientists to continue to study Spanish dancers, though, as this species lives on coral reefs, an ecosystem vulnerable to human-induced change.