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

Nigel Cattlin / Spanish slug (Arion vulgaris) with closed pneumostome on grass, light grey colour variation. Berkshire, England, UK. August.

Nigel Cattlin / Spanish slug (Arion vulgaris) on grass, tan colour variation. Berkshire, England, UK. August.

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

Robert Thompson / Spanish slug (Arion vulgaris) in garden, Banbridge, Co. Down, Northern Ireland. August

Robert Thompson / Spanish slug (Arion vulgaris) in garden, Banbridge, Co. Down, Northern Ireland. August

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

Claudio Contreras / Spanish shawl nudibranch (Flabellina iodinea), Salsipuedes Island Protected Area, Gulf of California (Sea of Cortez), Mexico, July

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

Alex Hyde / Spanish Slug (Arion vulgaris), Derbyshire, UK. August. Invasive species.

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