Do you ever feel... like a plastic bag? The blanket octopus (Tremoctopus spp.) surely does, having a mesmerizing swirl of billowing tentacles forming a kind of psychedelic cape. While the average swimmer might struggle to discern it from a wisp of floating plastic, marine biologist Jactina Shackleton was – safe to say from the squeaks of glee in her recording – very excited to ID this rare and beautiful animal.

“Today I had such an incredible snorkel and came across a BLANKET OCTOPUS!” Jacinta wrote on Instagram. “These animals are a rarely encountered pelagic octopus species that spend their whole lifecycle in the open ocean. The first live male was only sighted in 2002!”

Shackleton came across the young female blanket octopus on Thursday while swimming off the coast of Lady Elliot Island, a coral cay found at the southern tip of the Great Barrier Reef. The waters sit within a highly protected “Green Zone”, making it a haven for a diverse range of wildlife (including pink and melanistic manta rays) – but, as Shackleton puts it, seeing a female blanket octopus here is “surely a once-in-a-lifetime encounter”.

Hardly able to contain her excitement, or hold her breath as she snorkeled, Shackleton was fortunately still able to capture some photographs and video footage of the octopus, which is, quite frankly, just offensively beautiful.

Don’t be fooled by their beauty though, because the blanket octopus packs an unusual shiv in the form of an amputated tentacle stolen from a toxic jellyfish.

A blanket octopus was first seen alive by Dr Julian Finn of Museums Victoria, who said the species “illustrates the most extreme example of sexual size?dimorphism in a non?microscopic animal.” A good point well made, it has to be said, considering that while an adult female can be around two meters long (6.6 feet), the male sits at a paltry 2.4 centimeters (0.9 inches) constituting the largest gender size discrepancy in the animal kingdom

You might imagine mating would be difficult with such disparate sizing, and you’d be right. The process is a fatal one for the tiny males whose sex arm is broken off in the process, shortly after which they die.

Males are also somewhat lacking in the blanket department, an area in which – as the videos and photographs show – females excel with a breathtaking cape adorned with iridescence.

“Seeing one in real life is indescribable, I was so captivated by its movements, it was as if it was dancing through the water with a flowing cape,” Shackleton told Guardian. “The vibrant colours are just so incredible, you can’t take your eyes off it.”