Distribution: Common in the Solitary Islands Marine Park. Frequents open ocean throughout the Tropical Indo-Western Pacific region.

Ecological Notes: Found floating upside down on the ocean surface, where it feeds on colonies of Pacific Men-o-war, or blue bottles.

Additional Notes: The foot and under surface, as shown in the photograph, are brilliant blue, while the true dorsal surface, which faces downwards in the water, is silvery grey. This is known as countershading, and helps camouflage the animal from above and below. The cerata grow in multiple rows from each extension arch, while similar Glaucus atlanticus has cerata arranged in a single row around each arch. May sometimes be seen on beaches in relatively large numbers when blown ashore by onshore winds. The blue bottle is important not just as a food source, but also as a means of defense. After ingesting the man of war, the most potent nematocysts are stored in the bodies of Glaucus for defense, and can deliver a potent sting if handled carelessly. Grows to around 35 mm in length.

References: 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.