The likely culprits have been identified as amphipods, scavenging crustaceans sometimes called "sea fleas".
There are all kinds of strange, fascinating, and occasionally terrifying creatures in the ocean.
The latest to capture public attention — especially among people fascinated by Australia's long list of deadly animals — are the mysterious sea creatures that chewed and bloodied the legs of Sam Kanizay.
The 16-year-old went for a soak at a Melbourne-area beach after playing football, and reportedly emerged from the water feeling like he needed to brush sand from his legs. But his family quickly noticed he was bleeding profusely from what looked like hundreds of tiny pin holes. They rushed him to the hospital, where puzzled staff tried to figure out what caused the pools of blood to form around Kanizay's ankles. (A graphic photo of the wounds can be found near the bottom of this post.)
Initially, a number of reports referred to the culprits as "sea lice," a term that refers to more than 500 species of parasites that feed on fish.
But Kanizay's father decided to return to the beach to see if he could draw out the flesh-eaters again. He dropped little hunks of meat into the water, and saw that they were promptly swarmed by tiny scavenging crustaceans, as shown in the YouTube video below.
Marine biologist Genefor Walker-Smith of Museums Victoria identified the creatures as lysianassid amphipods, little scavengers that are sometimes called "sea fleas."
She said the creatures do occasionally bite, but not with the severity that was evident in Kanizay's case.
(Warning: the following image is bloody.)
The amphipods may disperse an anti-coagulant when they bite, which would explain why it was so hard to stop the bleeding.
"It was just unlucky. It's possible he disturbed a feeding group but they are generally not out there waiting to attack like piranhas," Walker-Smith said.
Still, the presence of these crustaceans in the water doesn't prove they are the ones that attacked Kanizay's ankles. People have often mistakenly blamed sea lice for bites by jellyfish larvae in Florida and the Caribbean. And the ocean is full of other animals that may occasionally decide that something sitting there looks worth a taste — though these incidents are rare.
Marine ecologist Alistair Poore gave Australian Broadcasting Corp. his best advice for avoiding these sorts of creatures in the rare event that they appear: