She's the universe's perfect killing machine.

The Xenomorph begins life as a squid-like 'facehugger'. Then she lies inside her host – a human space-traveller, or perhaps a pet dog – before the dramatic 'chest burster' scene. Finally we are confronted with a cross between a human and an insect with a jaw that shoots out to kill its prey, and acid blood that burns through metal.

Meet Alien, who has been terrifying cinemagoers for more than a generation. She has made a gory reappearance in Alien: Covenant, the sixth instalment of this iconic space-horror franchise.

But while undeniably scary as hell, the face hugging, chest bursting and acid blood seem biologically implausible. Or are they? When you look deep into nature there are plenty of examples that are just as weird and scary, with victims who are just as unlucky.

Here are six animals here on Earth that could give the Alien a run for her money.

THE SARCASTIC FRINGE-HEAD

While it's not exactly a facehugger, it really looks like one. The sarcastic fringe-head fish has a mouth that rivals Mick Jagger's, and an attitude to match.

This small marine fish, which lives along the Pacific coast of North America, aggressively defends its territory from all-comers, and uses its giant mouth to do battle with its rivals.

It might look like an awkward display of kissing, but fish biologist Dr John Morrongiello says it's actually a battle between two males to determine which fish has the biggest mouth, with the winner taking dominion over the loser's territory.

"In fish, a feature like this can also be used in courtship displays, but in this animal it is mainly used in territorial aggressive interactions," says Dr Morrongiello, from the School of BioSciences at the University of Melbourne.

When they're not fighting, the species lives a rather sedate lifestyle, choosing to burrow themselves in empty clam or snail shells.

They may not be sarcastic in the way we imagine, and they may not get the movie one-liners to match their name, but these fish look as alien as the Xenomorph.

THE GOBLIN SHARK

Drifting deep in space inside an escape pod you hide yourself in an air-duct, hoping to escape the terrifying clutches of the Alien. The ship goes quiet, then suddenly, before you have time to flee, the Xenomorph's extra jaw unhinges from its maw, dragging you to your death. It certainly reads like science fiction, but deep beneath the ocean, many animals live in constant fear of a similar fate.

The Goblin shark, which was named for its creepy appearance, can match the Alien when it comes to petrifying, hinged jaws. The ancient fish has a specialised jaw – with two rows of nail sharp teeth – that can 'catapult' out to snare its deep-water prey.

"The Goblin shark can protrude its jaws at an astonishing speed of 3.1 metres per second, and a distance of nearly 10 per cent of their body length," says Dr Morrongiello.

"This is equivalent to a human being able to stick their teeth 5-20cm out from their face.

"The goblin shark's rapid jaw extension allows them to quickly grab any prey they encounter in the deep, and makes up for their very slow swimming speed."

Lucky for us, the goblin shark lives at depths below 100 metres. In fact they have been found as deep as 1300 metres below the ocean surface.

THE HAGFISH

Slime. It's a cinematic trope that tell us that an alien is out to get us. And this particular deep-sea creature seems to have an unending supply of clear mucous. According to Dr Morrongiello, the hagfish, or slime eel, is the slimiest creature you are likely to come across.

"A 50 centimetre long hagfish can extrude slime from pores along its body that rapidly expands to 20 litres of sticky material when it comes into contact with water," says Dr Morrongiello.

"If attacked, a hagfish will instantly clog the predator's mouth and gills with slime, forcing it to spit the fish out so it can clean itself."

This is a highly effective predator avoidance mechanism, but the downside is the hagfish also ends up with its own gills and body covered in slime. However, Dr Morrongiello says hagfish have evolved an ingenious way to rid itself of excess slime.

"It ties its body in a knot, and then slides this knot up its body, squeezing the slime off itself."

Ingenious, and truly alien.

THE HIPPOPOTAMUS' ACIDIC 'BLOOD'

In the first Alien movie, in 1979, chief engineer Dennis Parker says she has "a wonderful defence mechanism. You don't dare kill it". He's talking about the Xenomorph's weaponised, acidic blood that's strong enough to burn through several levels of the ship's hull.

But there's an earthbound animal that also bleeds acid. Unexpectedly, it's the hippopotamus.

When basking in the sun, hippos develop a red layer over their skin and for years it was thought they sweated blood. This myth was finally dismissed in 2004, when researchers discovered that hippos were actually secreting a kind of acid from their skin.

This red-coloured acid, called hipposudoric acid, acts as a sunscreen, and has antimicrobial properties that provide protection from bacteria and other microbes.

Professor Mark Rizzacasa, from the School of Chemistry at the University of Melbourne, says this unusual acid is an example of nature's chemistry laboratory at work.

The acid has now been synthesised by chemists, and while it's not going to burn through your spacecraft, Professor Rizzacasa says it could be used one day to add sun protection to everything from sunscreens to paint.

THE PARASITIC WASP

If any creature lives its life like the Alien, it's the crypt-keeper wasp. That's at least if you are a gall wasp.

These North-American wasps lay their eggs inside a tree chamber drilled by another wasp, the hapless gall wasp. When the egg hatches, the larva burrows into the body of the gall wasp and takes over its mind, controlling its every movement.

The gall wasp is forced to crawl out through an opening in the chamber by its parasitic passenger. But, sadly, the opening is too small for the gall wasp, and it dies in the attempt. The crypt-keeper wasp then emerges from the head of the dead gall wasp and out into the open air.

Professor Ary Hoffmann, from the School of BioSciences and Bio21 Institute at the University of Melbourne, says the crypt-keeper wasp is an example of a 'hyperparasitoid'. The gall wasp is itself a tree parasite, and so the crypt-keeper wasp is a parasite of a parasite.

"Parasitoids are important in agriculture because they help control aphid and moth pests," says Professor Hoffmann.

"However we also have a lot of hyperparasitoids and these in turn can reduce the effectiveness of the parasitoids. Unfortunately they are very poorly studied as a group in Australia - many have not even been named."

And Professor Hoffmann wonders if perhaps some of these unnamed hyperparasitoids might match or outdo the story of the crypt-keeper wasp.

"No doubt there are many interesting behavioural manipulations that these wasps mediate that remain to be discovered."

We can't wait … not.

THE CANDIRU

Nicknamed the 'vampire' fish, the candiru is a parasitic catfish that's native to South American countries including Brazil, Peru, Colombia, Bolivia and Ecuador.

You may have heard of this creature. It earned its alien comparison through stories that it swims up the urine stream and into the human penis via the urethra. These stories date back to the late 19th century but, although terrifying, no cases have actually been scientifically proven.

"The evidence for them entering human genitals by swimming up pee streams seems not well supported," says Professor Stephen Swearer, a marine biologist in the School of BioSciences, University of Melbourne.

In reality, the fish is too big to enter the urethra (it is about 17cm long) and it would need a rather powerful push to enter the small hole against a fairly strong current.

But that's not to say that this fish has no place in a horror movie franchise. It is, after all, a blood-sucking vampire fish.

"Basically this fish is a highly modified species of catfish that has evolved a morphology adapted to a parasitic lifestyle," says Professor Swearer.

"It attacks larger fishes near their aorta by attaching to the fish inside their opercular cavity - where the gills sit and where it's easy to get a blood meal."

So although we may be safe from the acid dripping, face hugging, chest destroying extraterrestrial Xenomorph for the time being, if these real animals decide to turn against us, it may only be a matter of time...

Banner Image: Luivisi/After H.R Giger animated by Sarah Fisher.