An Aussie made a baffling discovery this week on a beach in Sydney's south, and the unusual find left many questioning what it is.
"Does anyone know what this is? Have seen a number of these washed up this week," the Sutherland Shire local wrote on Facebook, and she wasn't the only curious person.
Another woman from the area said she'd seen them too when she was walking her dog along the sand at Darook Beach in Cronulla.
"They are everywhere," she said. "I was also wondering what they are."
Mystery creature explained: 'A local Sydney species'
The slug-like creature was a mystery for many with some comparing it to an "alien." But Yahoo News Australia can confirm it's nothing of the sort.
The creature is a sea hare, revealed Harry Masefield, Aquarist at Sea Life Sydney Aquarium. They're also commonly known as sea slugs, he added.
Sea hares are usually dark purple or green in colour and can be the size of a football. They release a purple dye, much like a squid, and can be extremely harmful to pets.
The sea animal has a life cycle of one year, Dr Lisa Kirkendale, head of aquatic zoology at the Western Australian Museum, told the ABC and when dead, they wash up onto the shore.
Aquarist Laetitia Hannan from Sea Life Sydney Aquarium suggested there are many sea hare species, but this one in particular is most likely Aplysia sydneyensis, a local Sydney species.
"We actually have these guys in our rock pool for people to look at and feel as they are super interesting to touch," she said.
"They camouflage themselves as rocks to stay safe from other animals eating them."
Meanwhile, black sea hares are often spotted on the west coast of Australia, and around March every year, hundreds wash up onto shore.
A warning for dog owners
Some people in the Facebook comments guessed correctly, saying the photo looked like a sea hare, but warned dog owners to "be careful" because of their toxic state.
Professor Culum Brown, from Macquarie University, explained sea hares derived their toxicity from the algae they graze on.
"They are only harmful if you eat them, and even then only some of the time," he told Yahoo News Australia.
"People don't munch on them but occasionally a dog might try should it find one washed up on the beach. If the individual hare has been eating particular types of algae it may cause harm to the dog."
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