Inside Nature’s Giants

Giant Squid

Architeuthis dux

Tom Mustill

© David Shale/naturepl.com

Deepsea squid (Histioteuthis sp) close-up of mantle showing photopores in the Atlantic Ocean.

There was one creature that members of the Inside Nature’s Giants team had set their hearts on from the start, a terrifying and mysterious alien. A predator that stalks the most inhospitable parts of our planet: the giant squid. These monsters of the deep can grow to 13m in length, yet we know almost nothing about them. Almost everything we know comes from studying the anatomy of the few rare specimens washed up on beaches or cut from the bellies of sperm whales. Sometimes research ships probing the sea’s depths around New Zealand will return with freshly caught specimens which they freeze in their holds. After months of negotiation we’d been allowed access to one of these rare catches.

Getting access was only the first hurdle. This is an animal with no hard parts and with the colour and consistency of custard. To enable our audience to distinguish its bizarre features we decided to perform the dissection on a specially built light-box. The strong under-lighting would reveal the giant squid’s inner secrets.

All the animals we planned to dissect, from elephants to whales to tigers, appear different, but are actually rather similar. They have four limbs and one heart, and once cut open their muscles and organs are recognisable as lungs, hearts and guts. But the giant squid is a 10-limbed, jet-propelled sac. Inside it has three hearts pumping blue blood, powering a beak attached to a gut, which runs through the middle of its brain. It is deeply strange.

Unlike our other giants, the giant squid has never been filmed alive in its natural habitat deep in the ocean. There are a few grainy photographs taken from a fishing line that show flailing red limbs and a short video showing the powerful death-throes of an animal hauled to the surface from the deep. Our expert Dr Steve O’Shea thought it would be a good idea for Joy to experience live squid, first-hand, to see how the basic anatomy works. Unlike the giants, we can catch and observe their smaller cousins from a boat in the calm waters of Russell, a quiet seaside town on the Pacific Coast of New Zealand’s North Island.

At least that’s the theory. We’re onboard and everything is in place. The sonar is showing a nice thick layer of krill that should tempt the squid. We can see hordes of these tiny shrimp-like animals swarming around. Suddenly a call goes up, ‘Squid!’ A bright white rocket shoots through the water as the jigging rod pulls a foot-long arrow squid aboard, where it is quickly transferred to the tank. It pulses around in tight circles, changing colour constantly from ferocious red to glaring silver. Steve thrusts his hand into the tank and deftly, but gently, points out the rows of suckers along each arm and at the centre of them the fiercely gnashing beak – two sharply interlocking points/folds of chitin.

© Jo Moore / Museum of New Zealand Te Papa Tongarewa

The giant squid is a 10-limbed, jet-propelled sac, with three hearts pumping blue blood, powering a beak attached to a gut, which runs through the middle of its brain.

© Eriko Sugita/Reuters/Corbis

The Japanese researcher Tsenemi Kubadera looks at images of the giant squid he captured at depth in 2004.

Spread out on the dissection table, the giant squid’s mantle is as big as Joy and its arms stretch the full length of the table.

He demonstrates how the main body of the squid is covered with a large muscular ‘sock’ called a mantle. The mantle, which contains the organs, contracts and relaxes, pulling water in to bathe the gills with oxygen, pushing it out through a funnel. This can be orientated in any direction, giving the squid a jet-propelled boost and incredible acceleration. Steve shows how the squid avoids blowing itself in half by joining the two parts of its body with a T-shaped locking mechanism. This neatly joins the mantle to the rest of the body. With a sucking noise he teases the two apart. The squid quickly re-engages the mechanism and jets away flashing murderous colours, its arms tucked up, holding the two feeding tentacles inside.

On the glowing dissection table the giant squid is laid out, its arms spanning the length of the table. Its two much longer feeding tentacles give it a total length of about 4m (13ft). It’s the anatomy of these long tentacles that Steve thinks gives a clue to how the giant squid hunts. Each sucker is encircled by a hard ring of teeth, like a set of jaws. Each squid has thousands of these jaws, which can bite deep into whatever the tentacles and arms touch.

© Jo Moore / Museum of New Zealand Te Papa Tongarewa

The giant squid’s beak is nestled in the centre of its arms. It is one of the only hard parts of the animal and is surrounded by jellied tissue.

Dr Steve O’Shea demonstrates how even a small squid’s beak is capable of quick and powerful bites on an arrow squid caught off the North Island of New Zealand.

Steve points out that when you place the two long tentacles side by side the strange knobs and suckers line up precisely. He thinks that these act like press-studs, zipping the two long tentacles together. He imagines the giant squid hanging 500m (1,640ft) deep in the water, with two tentacles dangling beneath. There it waits for its prey to pass between the two open clubs. When it does, the tentacles snap together to trap it.

But however the squid uses its tentacles, there are no bones to push and pull against. Joy thinks she can explain: she compares the tentacles to our tongue – it doesn’t have bones either, but you can still stick it out and curl it into a U-shape.

Mark scans the skin surface with a digital microscope. The patches of intact skin appear naturally dark red, but as Joy looks more closely she sees that this colour comes from lots of tiny dots embedded across the surface, called chromatophores. They are tiny sacs of pigment, controlled by muscles. When the muscles contract, they stretch the sacs of pigment, so that the dark areas expand. When this happens the colour changes from the yellowy-white to dark red.

Hanging at great depth, where red light cannot penetrate, being dark red is good camouflage. But if it has the ability to rapidly contract and expand its chromatophores, perhaps the giant squid can flash bright white in the dark, to stun prey, or confuse its predators?

Nestling snugly in the centre of the giant squid’s arms is its beak – a fearsome slicing tool – and one of the only hard parts of the animal. But it’s surrounded by tissue the consistency of jelly – like a knife with a butter handle. Only the beak’s tip is really hard and it gets progressively softer where it attaches to the soft body of the squid. This stops the squid from carving itself when it opens its mouth.

© Jo Moore / Museum of New Zealand Te Papa Tongarewa

© Eriko Sugita/Reuters/Corbis

Each sucker is encircled by a hard ring of teeth, like a set of jaws. Each squid has thousands of these jaws, which can bite deep into whatever the tentacles and arms touch.

No bones about it

Joy Reidenberg

Ten long, wiggly extensions sprout from one head. Sounds like the mythical Gorgon, but this is no myth: it’s the giant squid. Giant squids are cephalopods (literally ‘head-feet’), a group characterized by a head with multiple appendages. This feature separates them from other molluscs, such as one-footed snails.

Cephalopod appendage movements are mesmerizing. I was fortunate to experience seeing this while scuba diving with a giant Pacific octopus. The octopus trailed its arms, flattening them like a stealth bomber’s wings. It crawled over rocky surfaces by extending an arm, and then pulled the whole body towards that arm’s tip. Its most peculiar locomotion was on the sandy sea floor: the arms coiled and uncoiled under the body, and appeared to roll like wheels with suckers for treads. It even held its body up and used two arms to ‘walk’. But how does it do all this without a skeleton? The answer lies in its muscular anatomy.

A skeleton increases mechanical advantage through the arrangement of joints as levers or pulleys. Cephalopods, lacking bones, probably use more energy than vertebrates to generate movements through muscle contractions. However, their nearly weightless condition in water counteracts any energy debt. The lack of bones and joints provides exceptional flexibility and range of motion.

Bending occurs when muscles running along the arm’s length contract on only one side and relax on the opposite. Retraction involves contracting all of these muscles at once. Extension, however, is paradoxical. Muscles girdling the perimeter shrink the arm’s diameter. However, since there is no hollow core, there is no collapsible space to accommodate narrowing. Rather, compressing the outside propels fluids in the core – like squeezing a tube of toothpaste. Contractions begin near the base and progress peripherally, elongating and rigidifying the arm as fluids move to the tip. The uncurling and extending arms remind me of a New Year’s party blower. The same mechanism shoots the tentacles forward towards prey.

1. Central Intelligence

The squid’s narrow oesophagus passes through a doughnut-shaped brain. If there is a central intelligence in the squid, this tiny ring is where it lies. In the giant squid the brain is dispersed around the animal. The optic lobes process visual data and even the squid’s arms have their own decentralized processing areas. If the arms are severed they can touch, react and manipulate the world around. Certain cephalopods are thought to be ‘smart’. In captivity, octopuses can be trained to navigate mazes and to open jars: aquaria give their octopuses toys to keep them amused.

2. Arms

The giant squid has eight arms encircling the beak. It’s thought that these are used to subdue struggling prey once captured by the two enormous feeding tentacles, holding them tightly with row upon row of jawed suckers against the beak as it chews them into pieces.

3. Protective Ink Sac

A dark chamber positioned above the anus of the squid is the ink-sac. It is the last resort when confronted by a threat. For the giant squid this would most likely be its nemesis, the sperm whale. Bits of skin around the anus – anal flaps – are muscular and can control how the ink is expelled, a great diversionary ploy.

4. A Tongue With Teeth

The beak of the giant squid might be fearsome, but lurking inside is a tongue glittering with rows of hooked teeth. These rasp across food particles, blending them into a soup thin enough to pass along the oesophagus and through the ‘brain’.

5. Reproduction

Giant squid sex is an unusual affair. The nidamental gland – the reproductive organ of female squids – is a fluffy mass of tissue deep in the mantle of the squid. When squid sexually mature they stop feeding and plough all energy into reproducing. Once a female octopus is fertilized she will lay her eggs and guard them, keeping them fresh and oxygenated. When they hatch, she dies. The female giant squid will collect a number of sperm packages, which are embedded in her arms, perhaps from a number of different males. When her eggs are ready she’ll extrude them through her funnel and nestle them in her arms, where they’ll trigger the sperm packages to explode through her skin and onto the eggs. This moment of fertilization could take place long after the sexual encounter.

6. Eye

The lens of the giant squid is split into two hemispheres, joined together, and held in place by a sphincter around the outside. The eye itself is enormous, but the retina that the lens focuses the light onto has the highest acuity of any animal.

7. Huge Optic Lobe

The eye of the giant squid is actually similar to our own, but it has evolved this form and shape independently. It’s a classic example of convergent evolution where the same basic layout evolves on a completely different branch of the tree of life. The huge optic lobe is where the squid processes visual information to respond with deadly precision.

As Richard Dawkins says, ‘The science fiction author Arthur C. Clarke, who obviously loved writing about space fiction, also made the point that we know less about the deep sea than we know about the moon. We can’t unfortunately go to distant planets to see what alien life might be, so maybe the deep sea is the next best thing. Who knows what else we may find down there?’

© Brian J. Skerry/National Geographic/Getty

With angry eye and a cloud of ink, a jumbo squid flees from a diver.

Inside the beak is the next extraordinary piece of the giant squid’s feeding apparatus. It’s a strange fleshy, tongue-like structure, covered in tiny teeth. This is called a radula, and is common to many molluscs; it’s what snails use to rasp through lettuce. In the giant squid it rasps against the chunks carved off by the beak, turning them into a sludge that can pass safely down the thin oesophagus towards the digestive gland. This amorphous, brown sac full of enzymes breaks down the protein in its diet of smaller squid and turns it into giant squid. The giant squid grows extremely fast, from a 2mm (0.08in) infant to a 3m (10ft)-apex adult in five years. Joy inspects the oesophagus and finds it passes through a narrow ring of tissue like a Polo mint of white matter. This is the central brain of the giant squid.

The squid’s internal organs are enclosed within its mantle. Inside, the anatomy is a confusing mass of delicate tubes and foul-looking sacs flanked by two large white feathery structures. These are the gills, where the giant squid pulls oxygen from the water and ditches carbon dioxide. The squid needs a great deal of oxygen to power its huge muscles, so these gills are very different from the gills of a fish. At the top of each one is a small round sac that’s full of blood.

Joy injects ink into one of the sacs above the gills; from here the ink spreads delicately into and through the gills in fronds across the surface. Joy fills the central heart and other gill heart with ink and as it drains through the blood vessels this extraordinary anatomy is suddenly clear. Steve explains that the sac is actually a heart. Each of the two gills has its own heart, to pump the deoxygenated blood from the body into each gill. It then drains back to a third central heart, which pumps the oxygenated blood out to the rest of the body. But having three hearts is not quite so bizarre as it first sounds. Humans have a dual blood flow circuit for which we use not three but four bags of muscle – it’s just that these four small hearts are enclosed within a single organ.

In the bright under-glow of the light-box it looks like a totally alien creature, but perhaps we’re not as different as we’d like to think.

© Franco Banfi/NHPA

Whale

Balaenoptera physalus

David Dugan

© Michael S. Nolan/Specialist Stock/Corbis

The car bumper sticker says it all: ‘Courtmacsherry, a quiet drinking village with a fishing problem’ – although what they have today is more of a marine mammal problem. As the car headlamps sweep across Courtmacsherry Bay in West Cork, we catch a glimpse of the half-submerged fin whale that has stranded on a falling tide. Despite the efforts of local fishermen to re-float her at high water, this 20m (66ft) giant was doomed. Her distant ancestor may once have walked on land, but when a whale this size beaches the full force of gravity crushes its internal organs. Sadly, she died, and the Irish authorities have a mountain of decomposing flesh on the beach. We are here to persuade them to let us carry out a full dissection.

The man in charge of this problem is Dan Crowley, the County Cork veterinarian, whose priority is to dispose of this whale as fast as possible. So far it has not been going well. County Council workers attempted to haul it up the beach away from the incoming tide. They put a big chain round the tail of the 50 tonne leviathan and attached it to a digger. In this unlikely tug of war between whale and machine, there was only ever going to be one winner. The digger sunk deeper into the sand until there was a resounding crack. The tail had come off. It was time to call in an expert.

Professor Joy Reidenberg teaches human anatomy to medical students at Mount Sinai School of Medecine in New York, but her research passion is marine mammals – particularly whales. As a comparative anatomist she’s probably been inside the mouths and down the throats of more whales than anyone on the planet. Her toolbox full of knives is always on stand-by. So when she received the call, she jumped on the first plane to Ireland.

Dan Crowley knew enough about whales to realise he was sitting on an unexploded bomb, but he’d never disposed of a whale this size before. His plan was to bring in excavators, dig a deep trench and bury it. At least, that was his plan until he met Joy Reidenberg. The Irish Whale and Dolphin Group set up a temporary crisis headquarters in their camper van where the delicate negotiations about dissecting the whale take place. Dan is impatient. There’s no time for dissection. He wants the carcass buried as soon as possible to avoid any public health risk. Joy shakes her head knowingly. She warns that his strategy will end in disaster. In a few days time the bloated carcass would re-surface no matter how many rocks were piled on top. The whale would come back to haunt them unless it was completely chopped up. Joy clearly knew what she was talking about. She sketches on a pad how the whale should be gently deflated and peeled open like a banana. Dan eventually relents and seals the deal with a spit-handshake. We have two days. Joy will help them get rid of the whale, if they let us carry out a dissection to explore its massive anatomy.

© walshphotos/Shutterstock

Courtmacsherry Bay on the coast of West Cork, Ireland.

© Tui De Roy/Minden Pictures/FLPA

The fin whale is the second largest species of whale after the blue whale.

The stranded fin whale draws a huge crowd of spectators. The fin whale’s gigantic mouth occupies most of the front half of its body.

Joy Reidenberg briefs the team from the Irish Whale and Dolphin Group inside their temporary camper van HQ.

The fin whale is a baleen whale. The baleen plates hanging from its jaws are used to filter krill and small fish which are eaten in vast quantities.

By now the tide has almost retreated, so we paddle across the last rivulets dividing the sand towards the whale which has now attracted a crowd of onlookers. After the blue whale, the fin whale is the second largest animal on the planet. To stand alongside such a colossal alien-looking organism makes you feel very small in the grand scheme of life.

While Joy prepares to make the first incision, Mark Evans, our veterinary scientist, inspects the bulging tissue that’s forcing open the whale’s mouth. The highly elastic tongue and floor of the mouth have inflated like a weather balloon. He prods it cautiously and marvels at how taut it’s become.

The pressure inside this whale is building up and Joy is nervous that there are too many onlookers oblivious to the threat. She knows that if they don’t act fast it could explode. Although it’s cold outside, the whale’s thick layer of blubber insulates the internal organs maintaining the heat inside. This accelerates the bacterial breakdown of the organs and releases more and more gas. By now the whale is almost double its normal size.

The ventral pleats on the whale’s underbelly have expanded like an accordion stretched to bursting