Glaucus atlanticus Forster, 1777

Several specimens of Glaucus atlanticus have been found washed ashore on windward beaches of Kwajalein and Enewetak Atolls. No pictures of those were taken, however, so the photos below are all of specimens from Hawaii.

Glaucus atlanticus floats upside down on the ocean's surface. In the pictures from above, the two dark lines running the length of the body are the sides of the foot. It almost looks like the animal is crawling on the undersurface of the air-water interface. What it does up there is eat floating siphonophores such as the Portuguese Man-o-war, Physalia physalis.

Like many other eolids, Glaucus keeps the undigested nematocysts (stinging cells) from the Physalia and stores them at the tips of its own wing-like cerata. Studies have indicated that the nudibranch's physiology somehow manages to sort out and select the largest and most potent nematocysts, so it is capable of giving at least as strong a sting as its man-o-war prey.

This is more the way you usually see them, washed in on the beach. The one below is still in a few millimeters of water in a shallow beach tide pool.

Created 8 January 2007