Glaucus atlanticus (Forster, 1777)
Common in the Solitary Islands Marine Park. Circumtropical in temperate and tropical waters. Recorded from the temperate and tropical shores of the Australian coastline.
Float on the ocean's surface, where it feeds on colonies of Pacific Men-o-war, or blue bottles.
This animal floats upside down in the water, the surface shown in the photograph in fact being the underside. The dorsal surface is silvery grey in colour. The cerata grow in single rows from each extension arch, different from its close relative Glaucilla bennettae, which has multiple rows from each arch and tends to have a less tapered, more stout body. Along with its relative it preys on blue bottles, and stores the most potent nematocysts in its body as a form of defense. Grows to 40 mm.
Gary Cobb, David Mullins, Nudibranchs Encyclopedia, 2nd Edition, 2015. Publishers Thomas Slone, Masalai Press and Tim Hochgrebe, Underwater Australasia. p.234.
Undersea Jewels, A colour guide to nudibranchs, Gary Cobb and Richard C Willan. Australian Biological Resources Study, Canberra, 2006. p.298.