Iron exoskeletons, terrifying hammers, the ability to be totally fine after being frozen for years… Marvel’s Avengers, or just some of the weirder sea creatures on our planet?
Iron Man the scaly-foot snail
The scaly-foot gastropod Chrysomallon squamiferum lives 2500m below the surface of the Indian Ocean, in the deep hydrothermal vents. And it has an actual iron exoskeleton, the only known animal to have this. The shell has layers of iron sulphide deposits combined with organic material to form an incredible armour that is resistant to blunt and spiky trauma, including the repeated squeezing that the snail’s main predators – crabs – cause with their claws. There are also iron deposits in the strange scales that cover the snail’s body. There’s so much iron that they can become magnetic, and go rusty.
Researchers are now investigating this unique structure, and wondering if it can be incorporated into technologies such as helmet design, armour, pipeline construction and making composites for aeroplanes and space rockets. The snail has other unique technology too – an enlarged oesophagus, in which different symbiotic bacteria live and produce an energy source for the snail that’s every bit as renewable as Iron Man’s arc reactor. Sadly for Tony Stark, it also has “no copulatory organ”, which is typical of snails in this family.
Thor the mantis shrimp
The peacock mantis shrimp smashes its prey with hammer-like forelegs, with a speed of 12-23 metres per second and a peak force of over 2500 times its own bodyweight. The shrimp’s hammers move so fast that the water around them actually vaporises when it hits something – a phenomenon called cavitation. When the cavitation bubble collapses, the forces it creates cause heat, light and sound, and considerably more damage to the prey than the initial impact alone. I’ve skipped ahead in the video below to the bit where you can see cavitation bubbles actually forming:
They can achieve this incredible speed by storing elastic energy in their hammer arms using strong, relatively slow muscle contractions, then releasing it quickly . The principle is similar to a crossbow (and also how frogs jump). The shrimp in the video is a girl, just like the latest Thor.
Black Widow the tasselled frogfish
Like Black Widow, the tasselled frogfish Rhycherus filamentosus is a master of disguise. It lives in Australian reefs and eats most things, including other fish, which it attracts by waving around a lure with an enticing fake worm on it. Once the prey approaches, the frogfish snaps open enormous specialised jaws, creating a pressure gradient that sucks water and prey into the mouth. The water flows out through the gills and the prey is not so lucky.
Captain America the tardigrade
Captain America spent decades frozen in the Arctic, before being thawed out with few ill-effects. Tardigrades, or water-bears, can do this too. There are over 1100 species of tardigrade, and they are found all over the globe, including under the sea.
These microscopic eight-legged animals can survive temperatures ranging from just above absolute zero (-273°C) to over 100°C. They can be dehydrated, put in a vacuum, and starved of water and food for over ten years.
They do this by turning into a “tun” – they retract their head and legs, dramatically slow their metabolism and reduce their amount of water. The glucose in their cells turns into a sugar called trehalose, which forms a gel and helps prevent cell damage. Trehalose is also used to preserve biological lab samples at low temperatures. Tardigrades can actually tolerate ice crystals forming inside their cells. No-one seems entirely sure how they do this, but it’s been suggested that trehalose and other substances ensure the ice crystals form without sharp edges, and stop the formation of larger crystals that would burst the cells.
The Hulk the yellow boxfish
Boxfish are called boxfish because they’re squarish. In fact, they have a bizarre box-shaped skeleton of fused bony plates under the skin. This makes them rigid and not very streamlined, and pretty slow in the water. Easy to eat, you might think, if you were a shark.
But you wouldn’t like them when they’re angry.
When they get stressed they excrete a totally unique toxin called pahutoxin (or ostracitoxin) from specialised skin cells, which makes the water around them poisonous. The toxin breaks down red blood cells, and is particularly effective at attacking the gills of larger fish like sharks. It also makes them a pretty unsuitable aquarium fish – put them in an enclosed space and upset them and they’ll kill all the other fish by mistake.
Hawkeye the possibly-imaginary escaped military dolphin with a dart gun
Believe it or not, this was a real story kicking about after Hurricane Katrina. The US Navy do have a dolphin-training programme, from which some dolphins may have escaped in 2005, but they deny that they have ever trained cetaceans to attack. Probably they’re telling the truth, but the US military were the people funding a psychic goat killing unit in the 70s and 80s, so they don’t always make sensible decisions.
Interesting reading (references are in the text):
- Patek lab – nice explanation of their work on the mechanics of the mantis shrimp.
- Water Bears on Ice – blogpost with all you need to know about tardigrades.
- Awesome boxfish post by someone doing a PhD on them – Boxfish: Little Fish, Big Toxin