A “fascinating” mound of wiggling sea creatures has stunned locals after washing ashore on a Sydney beach, leaving many perplexed and others pondering a “sinister” theory about their demise.

Vicki Hansen told Yahoo News Australia she was walking her dog along Greenhills Beach in the Sutherland Shire on Saturday morning when she stumbled across the clam-like creatures, comparing the moment to a scene from Stranger Things.

“I was surprised, but so many unusual things have been washing up on the beach lately, so I saw that it was yet something else that the ocean had carried to the shore,” she said.

“But I’ve never seen anything like these before.”

Vicki Hansen was walking her dog along Greenhills Beach in the Sutherland Shire on Saturday when she stumbled across the clam-like creatures. Source: Vicki Hansen, StoryCast

Photos and a video taken by Ms Hansen show thousands of the writhing shells attached to a long log by clear ‘tentacles’.

“I saw many that were hanging limply but as I bent down to study them I saw that some of them were moving, almost like a slow dance,” the videographer said.

“I figured that the limp ones had probably died from being removed from the sea, and that the ones that were moving were probably doing their last ‘death dance’.

“It was quite surreal, strange and beautiful at the same time.”

‘Missed out on a good snack’

Ms Hansen was not the only one to stumble across the creatures, with several other locals also posting images to Facebook in an effort to identify them.

“Wow, I was walking along Scotts Head beach on the Mid North Coast yesterday and saw the exact same thing! Kinda gross, kinda majestic and a whole lot of weird!” one woman commented.

“Hopefully the next high tide will take these little guys straight back out to sea,” another person hoped.

Numerous people were quick to claim that the creatures are in fact goose barnacles and are considered a delicacy in countries like Spain and Portugal.

“Damn, missed out on a good snack. They are delicious steamed with garlic parsley butter,” a man said.

Sea creatures on beach identified

The species of goose barnacles seen by Sutherland Shire residents are Lepas, which are mainly pelagic, meaning they live in areas of the sea away from land, Associate Professor Ian Tibbetts, with the University of Queensland’s School of Biological Services, told Yahoo News Australia.

“The are sometimes washed up on beaches when the object to which they are attached washes up on the beach, but they do not ‘live’ there,” he said.

“I have not seen any ever living intertidally. They attach to floating objects in the open ocean where the filter feed on plankton.

Several other locals also posted images to Facebook in an effort to identify the creatures. Source: Katie Hurley/Facebook

“I have seen them attached to the trailing edge of a 𝑏𝑎𝑏𝑦 dolphin’s fins – sad. They also will attach to sick sea turtles.”

Despite looking like a mollusc, goose barnacles are crustaceans and distant relatives of crabs and prawns, the associate professor added.‘Sinister’ theory emerges

The day after finding the barnacles, Ms Hansen said she passed by again but the creatures had died.

“Unfortunately there was no more movement and they were hanging limply, looking slightly brown and just a bit ‘off’,” she posted on Facebook.

The videographer said she also noticed some of the attached barnacles, which need water to survive, were missing and jokingly pondered if a local chef had something to do with it.

“Perhaps some had miraculously detached themselves from the log and returned to the sea,” she said.

“Or even more sinister — some local restauranteur had discovered their culinary value and is now adding a new dish to their repertoire.

“If you happen to see ‘Goosenecked Barnacles’ on a local menu, please observe a minutes silence for these strange, beautiful, but doomed creatures.”

However, Associate Professor Tibbetts said the Lepas species is not edible, unlike others like Pollicipes.