Sea Slug (Books)

Sea slugs are marine invertebrates mentioned very briefly in the How to Train Your Dragon Book series.

Description
'Sea slug' is a loose term describing any gastropod that lives in the sea and looks like a land slug. Creatures called sea slugs may be species of various taxonomic groups under Class Gastropoda.

Sea slugs typically occur in temperate and tropical marine habitats across the globe. Though they may appear soft-bodied and roughly cylindrical, most have other bodily decoration and come a bright and flashy colors. Some are ruffled and some have finger-like growths on their backs. Some species are poisonous, and some species may even steal stinging cells from jellyfish. The diet varies depending on species, and might include jellyfish, sea urchins, Plankton, barnacles, anemones, even other sea slugs.

How to Train Your Dragon
Seaslugs are mentioned once in the first Book. As part of Hiccup's plan against the Green Death, Fireworm taunts the huge dragon and calls him a seaslug.