Deadly denizens

Sheree Marris | VOLUME 31, ISSUE 6

It’s a fish-eat-fish world in the ocean, with a grizzly ending lurking behind every rock, sandy bottom or clump of weed.

Nature is the ultimate testing ground for what it takes to survive. It’s been trialling what works and what doesn’t for millions of years.

One of the primary ingredients for a species’ success is its ability to defend itself – but sometimes the best defence is offence. This concept has produced some of the most elite, innovative and lethal assassins on the planet and the best of these are found in the big blue. It’s an environment that is more ruthless than any metropolis or dimly lit alleyway.

In the marine world, reputation counts for nothing. The weaponry and tactics used to take down targets can range from cruel to cunning and, at times, even nightmarish. Some of these underwater assassins would make any would-be mobster shake in their boots. Under water, the sand swallows you whole, seaweed turns sinister and slayings are so speedy there is virtually no chance to escape. It’s more gruesome than any Hollywood blockbuster and, in some cases, is literally shocking. Life – and death – in the sea offers no second chances.

We’ve collected the most brutal, brilliant and downright ingenious practitioners of sub-surface slaughter. The rewards for these deadly denizens aren’t notoriety, fast cars or cold hard cash – they’re fresh flesh, scales, tails … and life itself.


Terrorising locals on sandy substrates in the tropics is a three-metre-long sand savage called the bobbit worm. Famed for its ruthlessness and serrated jaws that are twice its body width, these worms are the stuff of nightmares. Five antennae fashioned on its head help this marine menace detect any potential victims swimming or crawling above its hideout in the sand. If you make it onto the bobbit worm’s radar, chances are you won’t make it home to tell the tale.

Like an evil jack-in-the-box, the bobbit worm launches its deadly assault by catapulting from its burrow and unravelling a set of torturous, spring-loaded jaws that snap shut on their victims like a carnivorous trap. The prey is then quickly dragged down into its hideout for untold torture. These worms strike with such ferocity that victims are often impaled or sliced in half.


To make it as a hitman in the marine environment you need to be able to monitor the movements of your target without being seen. One of the best in the business is the tasselled anglerfish. Nothing escapes this guy. It’s craftily disguised as a piece of seaweed with camouflage so effective it can swim out in the open and not be seen.

Silent and still, it either waits for its prey to pass or lures it to its death with the promise of food by casting a rod and worm-like bait that is fused to its face. But as it demonstrates so well, in the sea there’s no such thing as a free feed. Any fish that tries to take the bait is swallowed whole in a nanosecond – no time for chewing! The tasselled anglerfish’s expandable mouth acts like a vacuum to suck up its prey. From beginning to mouth-filling end, it’s all over in a split second. Fish fall for the lure every time, hook, line and sinker.

Some assassins like to get dirty and let their fists do the talking. Enter the peacock mantis shrimp, aka ‘The Smasher’. It may be a shrimp, but boy can it pack a punch. It has arms fashioned with clubs at the tips that are designed to knock out and pulverise its hard-shelled victims with a single knock-out blow.

It packs a big punch for its size and has the fastest hit of any animal on the planet. Think a bullet fired from a gun is fast? This is faster. It’s so quick it creates a cavitation bubble. When the bubble collapses, a second shockwave of energy hits the already stunned prey – it’s a real double whammy. Even armoured crabs and snails don’t stand a chance. It’s why peacock mantis shrimp are called the fastest claw in the west, or should that be the wet …

The stargazer fish, meanwhile, awaits its targets by burying itself in the sand. It uses its pectoral fins like shovels to conceal itself in its sandy bunker. With its mouth located at the top of its head and using its eyes like periscopes, it waits patiently for the next passing meal.

When an unlucky fish swims by, the stargazer launches out of the safety of the sand with lightning speed, swallowing its prey whole. Muscles lining the mouth drag it to its doom. By the time a fish sees a stargazer, it’s already too late.


Some of the weapons employed by marine hitmen can be unconventional and seem almost innocuous. Such as the humpback whale – not your typical marine thug, but don’t be fooled by these ocean crooners. They use bubbles to round up their victims.

These ocean giants coordinate their killing by diving down beneath schools of squid or fish. One whale will emit a loud bellow that sends the school rushing to the surface in a panic, while another whale blows bubbles. The bubbles form a net, acting as a barrier that concentrates the panicked prey into a tight ball and preventing escape. A signal is then given and the whales lunge toward the surface with mouths wide open to devour the spoils. These marine mobsters each consume up to 1300kg of prey in a day during the feeding season.

Electric rays, on the other hand, use their muscle power and shock tactics to take down their victims. Their low profile allows them to blend into the bottom, where they wait patiently for their favourite meal to swim by. When something takes their fancy, they burst out from the bottom, propelled by their tail, wrapping their prey in a big ‘I’m glad to see you, can’t wait to eat you’ hug.

The ray delivers the coup de grâce with a burst of electricity that stuns or kills its target. Two large electric organs on the side of its head, comprising hundreds of muscle stacks, generate the shock when contracted. With its mouth underneath its body, the electric ray then lies on top of its prey and literally feeds its face.

The term ‘shark’ is often used to describe actions that swindle or trick victims. The wobbegong shark is the king of deceit – operating under the cover of darkness, this sharp shark will take you for everything you’ve got before you’ve had a chance to react.

Its deceit lies in its ability to disappear into the background. A mottled pattern and tasselled fringes running along its margins break up the outline of the wobbegong’s body and to the unsuspecting it can look like a rocky reef or ledge promising a safe refuge. It gives the wobbegong an unbeatable disguise and any passing fish little hope. The reef quickly turns into a mouth filled with dagger-like teeth for piercing prey, making escape impossible.

Unlike its toothy counterparts, the business end of the thresher shark is its tail. Also known as the Zorro thresher, it uses its tail to take out targets. Accounting for half the shark’s entire body length and one third of its total body weight, the tail is an impressive weapon indeed, considering that a thresher can measure up to five metres. Not only is it long, the tail is enlarged at the end to deliver a knockout blow.

These lone sharks corral small baitfish or squid into tight balls. They then charge through the school and stun their victims with a quick, whip-like strike of their tail. This can have enough force to break bones. Needless to say, this tail doesn’t have a happy ending for any victims. Stunned, dazed and confused, they’re quickly devoured.


The dapperly dressed harlequin shrimps are the Bonnie and Clyde of the marine world. Theirs is a lethal type of love, which sees them rampage through rocky reefs, working together to take down their target starfish.

It’s a highly specialised job that requires precision timing. Starfish have hundreds of feet covered with tiny suction cups that fasten them to the reef. Working together, the harlequins prise seastars from rocks and quickly immobilise them, flipping them onto their backs and making it nearly impossible for the starfish to defend themselves or escape.

Using their razor-sharp pincers they devour the stars’ sticky feet, working from the tip of the arm to the centre of the starfish. The nightmare continues when the fallen star is eventually dragged back to the shrimp’s den, where it becomes a living larder for the gruesome twosome. The shrimp will even feed the starfish in a bid to keep their meal fresh.

In the sea, as in space, no one can hear you scream. Or at least not if you become a victim of any of these stealthy assassins. These animals operate in a secret world, motivated by the need to feed. Successful hits are being carried out everywhere, every second. The key to success is stealth, innovation and adaptability.

If you’re now scared senseless and never want to swim in the big blue, consider this: unless you have scales, tails, feathers or fur, you’re pretty much safe from the clutches of these masterful marine hitmen.

Creature Features