blue dragon

Short definition from Wiktionary

Noun

1. 1
   A species of nudibranch sea slug, Glaucus atlanticus, blue in colour and living in the pelagic zone of the ocean.
2. 2
   A species of small, floating, blue nudibranch sea slug, Glaucus marginatus, looking very similar to Glaucus atlanticus.
3. 3
   A species of nudibranch sea slug, Pteraeolidia ianthina, ranging in colours from blue, yellow, and green.