Glaucus atlanticus Forster, 1777

Glaucus atlanticus floats upside down on the surface of the water, where it preys upon the floating siphonophore Physalia physalis, also called the Portuguese Man-o-war, as well as some other floating cniderians. They store potent stinging cells, or nematocysts, in the tips of their ceratal tentacles (what look like fins in the pictures below) and, like the man-o-war itself, are capable of stinging humans. Most specimens we saw were washed in on windward beaches during the windy season.

A typical way to find them is washed in on the beach along with their siphonophore prey.

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Created 20 April 2009

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