sea dragon

Short definition from Wiktionary

Noun

1. 1
   Certain fish: leafy sea dragon (Phycodurus eques)
2. 2
   Certain fish: weedy sea dragon (Phyllopteryx taeniolatus)
3. 3
   Certain fish: ruby sea dragon (Phyllopteryx dewysea)
4. 4
   Various sea animals that are likened to dragons: A blue sea dragon, a sea slug of species Glaucus atlanticus.
5. 5
   An ichthyosaur (dinosaur-age delphine marine reptile)
6. 6
   A type of dragon that inhabits oceans.