Jeff Rotman / Symbiotic emperor shrimp (Periclimenes imperator / Zenopontonia rex) living in the gills of a spanish nudibranch (Hexabranchus sanguineus) Red Sea, Egypt

Magnus Lundgren / Wild Wonders of China / Free swimming juvenile spanish dancer (Hexabranchus sanguineus) in the night, Kenting National Park, Hengchun Peninsula, Taiwan

Magnus Lundgren / Wild Wonders of China / Free swimming juvenile spanish dancer (Hexabranchus sanguineus) in the night, Kenting National Park, Hengchun Peninsula, Taiwan

David Fleetham / Imperial commensal shrimp (Periclimenes imperator / Zenopontonia rex) on Spanish dancer nudibranch (Hexabranchus sanguineus) at night. Philippines.

Tony Wu / Spanish dancer nudibranch (Hexabranchus sanguineus) scavenging the reef at night in Ambon, Indonesia

Pascal Kobeh / Diver in front of two mating Spanish dancers (Hexabranchus sanguineus) Madagascar. Indian Ocean. September 2012.

Alex Mustard / Spanish dancer nudibranch (Hexabranchus sanguineus) moves across coral reef in daylight. It is unusually to see this large nudibranch during daylight. Nuweiba, Sinai, Egypt. Gulf of Aqaba, Red Sea.

Magnus Lundgren / Wild Wonders of China / Free-swiiming juvenile Spanish dancer, (Hexabranchus sanguineus) Green Island, Taiwan.