A horrific video of hundreds of creatures believed to be "sea lice" consuming chunks of raw meat is doing the rounds on the internet.

The video has been shared by a Melbourne father who said that his teenage son was attacked by those carnivores when he went for a dip. Jarrod Kanizay said his 16-year-old son Sam went for a 30-minute sea bath at Dendy Street Beach in Brighton on Saturday (5 August) and came back with his legs covered in blood.

The boy was immediately taken to a hospital, where staff members were mystified by the "pin-sized holes" all over his legs, Jarrod said. His son is now recovering at Dandenong Hospital, he added.

In order to find out what exactly had bitten Sam, Jarrod went back to the beach. He placed a net full of raw meat in the ocean and was stunned to see hundreds of tiny creatures swarming around the portion.

"We found thousands of little mite-type creatures in our net. We put them in an Esky and brought them home and looked at them intently and let them swim in white dishes with red meat," Jarrod said.

"Interestingly, overnight they've essentially all clung to the meat and have been busy overnight eating it.

"No one knows what the creatures are. They've called a number of people, whether it's toxicity experts or marine exerts and other medics around Melbourne at least... [and] yep, no one [knows]," he added.

University of Melbourne marine biologist Professor Michael Keough told the Age that sea lice were a possibility.

He said: "They're scavengers who'll clean up dead fish and feed on living tissue. They're mostly less than a centimetre long, and so the bites they make are pretty small, and so that's more consistent with pinprick size marks.

"It's just food for them. Especially if he's been standing around for a long time, it's the chance for more of them to come in and start biting. [They will] just be attracted to a little bit of blood. And if he's standing in the water and he's cold [he] may not notice a whole lot of little bites."

The incident comes almost a year after a massive outbreak of tiny "sea lice" at Florida beaches. The outbreak reported in June 2016 along the Gulf of Mexico, caused painful rashes but not bleeding. The bites can often go undetected for hours after they attack. The tiny marine pests are almost invisible to the naked eye in the water and can get trapped in swimming shorts with the lining acting as a net.

The painful bites are sometimes referred to as "ocean itch" or "sunbather's eruption" and lasts from a couple hours to several days.

Sea lice
Sam Kanizay went for a dip at Dendy Street Beach in Brighton but when he came back his legs were covered in blood YouTube/ screengrab