Much of what we know about the blanket octopus comes from captive animals or long-expired museum specimens, but on very rare occasions these caped crusaders of the open water make an appearance, as if to remind us that they are still out there. Marine biologist and reef guide Jacinta Shackleton was lucky enough to share the water with a blanket octopus recently off the coast of Lady Elliot Island on the Great Barrier Reef, and captured some stunning footage to prove it:

"When I first saw it, I thought it could have been a juvenile fish with long fins," Shackleton told The Guardian. "But as it came closer, I realised it was a female blanket octopus and I had this overwhelming sense of joy and excitement." 

Sightings of these bright-red cephalopods – named for the iridescent sheet of flesh that encloses their tentacles like a cape – are very rare and, according to Shackleton, there have only been three other records of the animals in the area where this one was spotted.

Only female blanket octopuses sport the mesmerising 'cape' that gives the species its extra-special allure. If the octopuses are under threat, the wavy attachment can be shed in an effort to elude predators. 

Females are believed to grow to around 2 metres in length while the males on record max out at just 2.4 centimetres, which illustrates the "most extreme example of sexual size-dimorphism in a non-microscopic animal," according to a study published in the New Zealand Journal of Marine and Freshwater Research. This radical difference in size may be linked to the blanket octopus's nifty habit of carrying around sections of stinging tentacles from jellyfish as a means of self-defence. Both females and males have been observed wielding nematocysts (the stingy parts of jellyfish), but the strategy is only effective for smaller animals – larger individuals are unable to carry enough tentacles to defend themselves fully. So while the females outgrow the tactic as they get older, males stick with it. Their smaller size also allows males to mature more quickly which may help them get a jump on the competition.

Shackleton described the experience of spotting one of these unique animals in the wild as a "once-in-a-lifetime encounter" for which she is very grateful. "Seeing one in real life is indescribable," she told The Guardian. "I was so captivated by its movements, it was as if it was dancing through the water with a flowing cape. The vibrant colours are just so incredible, you can’t take your eyes off it ... I’ve truly never seen anything like it before and don’t think I ever will again in my life."

Top header image: Jacinta Shackleton