blue dragon

plural blue dragons

1. A species of nudibranch sea slug, Glaucus atlanticus, blue in colour and living in the pelagic zone of the ocean.

   Synonyms: blue sea dragon, sea swallow, blue angel, blue glaucus, dragon slug, blue sea slug, blue ocean slug

2. A species of small, floating, blue nudibranch sea slug, Glaucus marginatus, looking very similar to Glaucus atlanticus.
3. A species of nudibranch sea slug, Pteraeolidia ianthina, ranging in colours from blue, yellow, and green.
4. Used other than figuratively or idiomatically: see blue, dragon.