Head to head
Violet Sea Snail vs Blue Dragon Sea Slug
Violet Sea Snail
VS Blue Dragon Sea Slug
The violet sea snail and the blue dragon sea slug both live upside down at the surface of the open ocean and eat the same stinging, drifting prey, but they stay afloat in different ways.
| Violet Sea Snail | Blue Dragon Sea Slug | |
|---|---|---|
| Scientific name | Janthina janthina | Glaucus atlanticus |
| Group | A sea snail, with a thin, fragile, spiral shell | A sea slug, with no shell |
| Size | Usually about 2 to 4 cm across | Usually 1 to 3 cm long |
| Colour | A violet to purple shell, darker below and paler above | A silvery-blue slug with six finger-like clusters of tapering blue appendages |
| Staying afloat | Makes a raft of mucus-coated air bubbles and clings to it upside down | Swallows an air bubble held in its stomach to stay buoyant, drifting belly-up at the surface |
| Diet | Drifting surface animals such as by-the-wind sailors and Portuguese men o' war | Floating siphonophores and cnidarians such as the Portuguese man o' war, blue button, and by-the-wind sailor, and even violet snail eggs |
| Defence | Releases a cloud of purple fluid when disturbed | Digests the man o' war but keeps its unfired stinging cells, concentrating them in its appendages |
| Conservation status | Not Evaluated, but widespread across warm and temperate oceans | Not Evaluated, living about a month to a year, in temperate and tropical surface waters |
Violet Sea Snail vs Blue Dragon Sea Slug: common questions
How does each stay afloat?
The violet sea snail clings to a raft of mucus-coated air bubbles, while the blue dragon swallows an air bubble held in its stomach.
Which one has a shell?
The violet sea snail has a thin, fragile violet shell, whereas the blue dragon is a sea slug with no shell.
How does the blue dragon defend itself?
It keeps the unfired stinging cells of the Portuguese man o' war it eats, and concentrates them in its appendages, making its sting potentially more painful.