mollusk of the week!

hey guys :D i am relieved to finally be back with another installment of mollusk of the week! today's mollusk is a beautiful little critter with an otherworldly appearance...

this week's mollusk is: glaucus atlanticus, the blue sea dragon!

once again, a nudibranch takes the center stage! i am very, very fond of nudibranchs, some of nature's most visually-appealing creatures, and this flashy slug is a standout even among his kind. you can immediately tell why they call them blue dragons - their extravagant appendages look like intricate wings, almost, and the way they hover in the water gives them the appearance of a  dragon in flight... 

these particular sea slugs live in the pelagic zone of the ocean (the open ocean), using a gas bubble in their stomachs to float on the surface, tugged along by the wind and the currents. they actually float upside down in order to make use of countershading, facing their bright, blue underbelly toward the sky to camouflage themselves from predatory sea birds above while simultaneously using their silver/grey dorsal side to blend in with the surface of the sea, hiding them from predators lurking below. it really makes me wonder how they 'know,' so to speak, that the water looks blue from above and all that... i know most animals have instincts and ingrained behaviors from conception, so it's likely an entire evolutionary chain of trial and error that led them to this behavior, but it's just so fascinating to me.

speaking of fascinating, despite the blue dragon's diminutive size (they rarely grow larger than 1.2in/3cm), they are formidable predators! this is because they feed solely on venomous siphonophores - often mistakenly referred to as jellyfish because of their similar appearance and shared phylum - including the infamous portuguese man o' war, as well as other cnidarians and even some of their fellow nudibranchs. the poisons do not affect them at all; in fact, they appropriate the stinging nematocysts from their prey and store them in an even higher concentration in their tendrils, or cerata, giving them extremely potent venom able to paralyze prey much, much larger than themselves. even humans need to be careful about handling them, as even just one sting can land you in the hospital. who knew such a little slug could wreak so much havoc? 

anyway, here's a mini gallery of these rowdy little guys for your enjoyment :D

note: i found so many pictures of these guys just casually eating portuguese man o' wars and such. they look so feathery and delicate but they are vicious fiends! also there were lots of fake images i had to sift through... ugh. it was worth it, though. they're mesmerizing! here's a video of them if you'd like to see them live and in action :]

hint for the next mollusk: a relic of times long past, this chambered cephalopod has been around for over 480 million years!