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Marine biologists have finally solved the mystery of how the "vampire squid" feeds, and what on -- namely a delightful recipe of corpses and faeces washed down with its own mucus.

With a name like Vampyroteuthis infernalis (meaning, quite literally the squid from hell), this lonely cephalopod was never going to be chowing down on any ordinary fare. Residing around 900 metres deep in warm waters, where there is little oxygen, and reaching a size of just 13cm in adulthood, the vampire squid's life is a solitary one -- it even has its very own taxononomic order (Vampyromorphida), of which it is the sole member, being an unusual breed that has characteristics of both octopi and squid.


Its name, however, is misleading, according to research carried out by Hendrik Hoving and Bruce Robison of the Monterey Bay Aquarium Research Institute. Their findings, published in the Proceedings of the Royal Society B, reveal that the unusual cephalopod quite cleverly takes advantage of its environment, where there is little competition for food or threat of predators. "Vampyroteuthis' feeding behaviour is unlike any other cephalopod," explains the study. "(It) reveals a unique adaptation that allows these animals to spend most of their life at depths where oxygen concentrations are very low, but where predators are few and typical cephalopod food is scarce."

The vampire squid therefore feeds solely on "marine snow" -- the debris that falls to the ocean floor, not live creatures. Marine biologists have never before been able to prove this, finding stomach contents of the dissected cephalopods to be inconclusive.

Hoving and Robison proved the theory by not only examining the stomach contents of live cephalopods from southern California and Mexico, but by filming the specimens in their natural habitat using remotely operated vehicles and studying them in tanks back at the lab. When debris made of animal particles were sunk in the tanks, the pair witnessed the cephalopod extend a fine, long filament from its umbrella-like mouth, which contains a web of eight arms covered in suckers and spines called cirri. This filament (which extends to eight times its body length) would stick to the debris, and then be drawn back through the web of arms, where the edible particles are "cleaned" off the filament and covered in mucus secreted from suckers. This glued together combination of mucus and debris is then placed in the mouth using the cirri, and consumed. "The food items that we found in digestive tracts, in droppings and regurgitations and that we saw being consumed during in situ observations were not representative of captured live prey," states the study. "Instead, Vampyroteuthis' food consisted of agglomerated copepod parts, faecal pellets, diatoms, radiolarians and fish scales; often embedded in a mucus matrix. The most likely source of this eclectic mix is marine snow aggregates, including the feeding structures of larvaceans."

Speaking to Discovery News, Richard Young, a biological oceanographer not involved in the study, called the findings "spectacular". "Vampire squid have always had these really funny long things that stick out of their body, and scientists like me had no idea what they were used for. Now we know. [This] is one peculiar critter. I would be shocked if any other marine organism ate in such a way."

So it turns out the stealthy cephalopod -- which uses its massive 2.5cm eye to look out for food, cloaks itself in bioluminescence to hide its silhouette from predators and uses its filaments to safely extract marine snow from a distance -- has been getting a bad rap all these years, despite being possibly the only cephalopod to not eat live prey. It can now have its reputation adjusted -- the cephalopod should no longer be referred to as a vampire, but instead a detritivore: a creature that thrives on decomposing bodies and faecal matter. It might not be much of an improvement.