From territorial sharks to deadly shells, these are the world's most dangerous sea creatures
Millions of Australians grew up by the beach and spent their summers playing in the surf, never knowing deadly critters could be lurking just below the waves.
Keep reading to learn all about the world's most dangerous sea creatures, many of whom call the waters around Australia home.
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Striped pyjama squid
Striped pyjama squid are both venomous and poisonous; their bite contains a potent neurotoxin and their slime is poisonous, which they use as a defense mechanism to deter predators.
Despite their names, these toxic little cephalopods are found in the waters around Australia, measure just 8cm in length and are actually not squid at all — they're cuttlefish.
It's not yet known whether the slime is harmful to humans but it's probably a good idea to avoid handling or ingesting one anyway.
Crown-of-thorns starfish
Not only are crown-of-thorns starfish responsible for destroying coral reefs around the world, their venemous spines can also cause humans a world of pain.
Growing up to 80 cm in diameter, these huge starfish's spines (which can be up to 4cm long) are covered in dangerous plancitoxins which can cause liver damage.
They can also release dangerous saponins compounds when threatened, which destroy red blood cells.
Humans stung by these intimidating-looking critters can suffer pain, vomiting, swelling and in rare cases, anaphylactic shock and death.
Bristleworm
It looks like something you'd find in an Aussie backyard but the bristleworm is actually a venomous sea creature.
These little worms are covered in stiff, often venomous bristles which can break off easily when bumped or handled by humans.
The venomous species, like the fireworm, can cause rashes, itching, burning pain, and swelling for several days after initial contact.
Fire coral
It may not look like an animal but fire coral is actually a collection of colonial marine organisms.
They vary in size, shape and colour but all are made up of hard skeletons packed with tiny pores which allow them to stretch stinging tentacles out into the water.
Even the slightest brush against fire coral can leave humans in intense pain for days on end.
This is because of the fire coral's venom, which can also cause side-effects like skin irritation, stinging or burning pain, redness, fever, and hives. Thankfully the sting is nonlethal to humans.
Lionfish
They may be beautiful but lionfish are actually one of the more dangerous fish in the sea.
Their tall dorsal spines aren't just for display — they're actually full of potent venom that can cause nausea, breathing difficulties and even paralysis in humans.
Fortunately deaths from lionfish stings are very rare and usually only occur when the victim already had other existing medical issues.
Sea snakes
Sea snakes don't go after humans often but that doesn't mean these ocean predators aren't dangerous.
There are more than 70 species of sea snakes in the world, most of which are venomous, including this beaked sea snake which is loaded with venom even more potent than that of a cobra.
Symptoms after a bite include headache, a thick-feeling tongue, thirst, sweating, and vomiting.
Thankfully, most sea snakes rarely inject their venom when biting so human attacks and fatalities are rare.
Stonefish
These killers hide in plain sight in reefs and shallow waters around Australia, though most beach-goers wouldn't notice them until it's too late.
Stonefish are very ugly, very venomous creatures that use their expert camouflage to blend into the seafloor and coral so they can catch prey unaware.
Unfortunately, they can also catch humans unaware with their sharp dorsal spines that are loaded with venom that only releases under pressure. Say, for example, when a human foot lands on them.
Dozens of stonefish stings are recorded in Australia every year, however very few deaths have occurred since an antivenom was developed.
Blue-ringed octopus
Most scholars agree that blue-ringed octopuses have killed at least 11 people, though the true number could be as low as seven or as high as 16.
Despite being tiny and fragile-looking, these Australian sea creatures carry enough venom to kill 26 adult humans within minutes.
The venom produced in their salivary glands can cause nausea, respiratory arrest, heart failure, severe and sometimes total paralysis, blindness, and even death within minutes of a bite.
The worst part is that the bite itself is often painless, so victims may not realise they've been bitten until paralysis begins.
Cone shells
It looks like a pretty sea shell but picking this up off the ocean floor could land you in hospital.
Cone snails are equipped with venom-filled modified teeth that work like harpoons, shooting out of their shells to paralyse prey with a single jab.
Usually they feed on small fish, invertebrates and other cone snails but geography cone snails, which can grow up to 15cm long, are also dangerous to humans.
Their venom is packed with an estimated 10,000 active compounds and can cause respiratory paralysis resulting in death. According to a 2016 study, they've killed about 15 people in the last 30 years.
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