These Glaucilla marginata are blue sea slugs or nudibranches — soft-bodied, marine gastropod mollusks, according to wikipedia — from the east coast of Australia, but they can also be found along the east and south coast of South Africa, European waters, and Mozambique. The narrator also mentions that they eat “blue bottle” jellyfish, as they are immune to the venom.
A photo of their cousins, the Glaucus Atlanticus, has become popular online recently, with little surprise: they are phenomenal-looking, tiny, dragon-like sea creatures! The kid should see this!
