Glaucus atlanticus - The Blue Glaucus
Top: Comparison for size - the Blue Glaucus does not exceed 5-7 cm long, but that’s huge compared to its nearest relative, Glaucilla marginata, which generally doesn’t exceed 18 mm.
Bottom left: Method of locomotion - Blue Glaucus float on the top of the ocean thanks to a gas sac in their abdomen, with their “head” facing upwards, and their cerata (those feathery appendages) dangling down.
Bottom right: Blue Glaucus from above. Note the numerous finger-like collections of cerata - in a full-grown adult, each of these can contain a concentrated dose of nematocyst venom.
Have you met my favorite nudibranch yet? I’m sure you have, and it’s totally cliche to love it, but whatever! I am a nudibranch hipster; I loved the blue sea swallow before the internet even caught wind of its awesomeness. JUST SAYIN’.
These seafaring drifters will float along with the current for days or weeks without feeding, using very little energy, until they sense a suitable prey within range - as these guys don’t move terribly well in the open ocean, “within range” is never much more than a few feet away. Favorite meals of the blue glaucus include the sailor by-the-wind (Velella velella) and the Portuguese man-o-war (Physalia physalis), the latter of which is particularly venomous. However, the blue glaucus is not only immune to the nematocyst venom, but possesses the ability to actually determine which stingers are the most venomous, and concentrate the venom of many meals into each “fingertip”, along with the stinging mechanism.
While they are unlikely to put anyone’s life in danger because of its tiny size, the blue glaucus can be found with venom two-to-twelve times stronger than that of each nematocyst on a Portuguese man-o-war, and is extremely painful when agitated. Though stings to humans are relatively rare, they apparently feel much like a bad hornet sting, with radiating burning pain, and both localized and generalized symptoms.
Taxonomy of Glaucus atlanticus. Natural History Museum of Britain.
Voyage dans l’Amerique meridionale. Alcide d’Orbigny, 1837.