Super-shrimp (are actually A Thing)

Posted: September 23, 2015 in Uncategorized

Sometimes, it seems like evolution just isn’t fair.

This is, of course, because evolution is a blind process driven by random chance, but still, the point stands. Evolution has hardly distributed her gifts equally. Some species got nothing more than the ability to survive by doing something horribly foul, usually inside an intestinal tract, whilst others…well, others more or less got it all. Like that one friend/person we’d all like to see die horribly we all have, who competes regularly in some extremely demanding sport. And is the smartest person you know. And has a high paying job. And is constantly going on holiday to attractive places with attractive people. And, just to put the cherry on it, is so damn likeable and self effacing that you can’t even have the satisfaction of hating them.

Mantis Shrimps (found in the order Stomatopoda, although all living ones are found in the sub-order Unipeltata) consist of 400 species and somewhat resemble the above friend. Minus the ‘likeable’ bit, but, as you’ll see, when you’re the Mantis Shrimp you don’t need ‘friends’. Not when you’re a foot long crustacean, living in a burrow in the sea bed, and able to kill things many times your size just by punching or stabbing. 

So its okay to hate them, I guess, if hating multi-coloured crustaceans is your thing. (Mantis shrimp is Odontodactylus scyllarus, image is from Wikimedia Commons).

They feed on marine invertebrates, and sometimes smaller fish. Depending on which food source they feed on, they can be divided into either ‘spearers’ or ‘smashers’. Both, however, use the same underlying hunting technique, which to give it is technical term is known as ‘punching the hell out of it’. The forelimbs of the shrimp terminate in a hard ‘tip’ called the dactyl – ‘smashers’ have a ball shaped dactyl whilst ‘spearers’ have a sharp, pointy dactyl.

Have a guess for yourself which one belongs to a ‘Smasher’ and which one to a ‘Spearer’. First correct answer wins 10,000 points! (Points are not redeemable in any nation and possession is an act of terrorism in Germany). Image from http://nirmukta.com/2014/01/27/into-the-world-of-mantis-shrimps/

The Peacock Mantis Shrimp, aka Odontodactylus scyllarus, strikes with a speed of 14 – 23 metres per second – which is rather impressive, all the more so when you realise the shrimp is doing this whilst underwater. The vast majority of you will grasp the key point here instantly, but for the small minority of this blog’s readers who don’t regularly attend illegal undersea fighting pits, its a lot harder to throw a punch in water than on land, owing to all the…well, water. In fact, just two and a half metres of water can shot a round fired from a handgun, and higher velocity rounds (fired from a sniper rifle, for instance) tend to disintegrate.

So we do not really recommend a large scale assault on the world’s oceans to destroy the Mantis Shrimp.

The mantis shrimp throws this punch in under three thousandsths of a second. This sort of strength comes from a very large amount of energy released very quickly – in fact, much quicker than would be possible if the strike was mostly driven by muscle power.

Especially your muscle power, puny human. (Image is from Wikimedia Commons, the shrimp is the wonderfully named ‘Pink Eared Mantis Shrimp, aka Odontodactylus latirostris.

Instead, what appears to happen is that the shrimp uses its muscles to prime a spring like mechanism inside its arm. A ratchet locks the arm firmly in place, to prevent the arm extending before the time is right. The large muscles in the upper arm then contract and build up energy over time. Furthermore, a saddle shaped piece of chitin is compressed as this happens. When the arm is released, the saddle expands, and the whole arm moves forward incredibly quickly – so quickly, in face, that one of the researchers had to borrow specialised high speed cameras to actually capture the movement in the first place. Its a bit like us slowly drawing an elastic band back, putting energy in over time and then letting go of it so the elastic band flies forward rather quickly, all the energy released at once, but approximately 30,000,000 times more impressive.

Obviously, this results in a very powerful punch – one which has been compared to a rifle bullet. Interestingly, in the case of ‘smashers’, the damage actually comes from two sources. First (rather obviously) is the damage caused by the actual punch itself. Secondly, however, is the force caused by the collapse of a ‘cavitation’ bubble. Since the dactyl moves so quickly through the water, areas of extremely low pressure are created. When these small bubbles collapse, even more energy is released, acting as a second punch which is normally about as half as powerful as the first, but on occasion can be three times as strong. Normally, cavitation damage is something designers of high speed boats and the like have to deal with, but the Mantis Shrimp not only create cavitation bubbles, they use them to their advantage.

The collapse of the cavitation bubbles can cause sonoluminiscence – the emission of tiny, brief (as in, thirty five to a few hundred trillionths of a second long) flashes of light by a mechanism scientists don’t yet understand, but might involve the rather awesomely named Bremsstrahlung radiation. Inside the cavitation bubbles it is thought that the temperature could rise higher than the surface of the sun (5, 500 or so degrees centigrade) – although since the bubbles are, by this point, very small, the mantis shrimp gets its food already tenderised, but not cooked.

Although perhaps if you got several thousand mantis shrimp, and set them all to punching each other….(Shrimp is Gonodactylus smithii, image is from Wikimedia Commons)

Mantis shrimp are terrifying in other ways. Because many of them are punching so fast, you might think their dactyls would soon disintegrate. However, the limp is designed to prevent this happening. Right at the front of the dactyl are hydroxyapatite crystals (the same material which makes up our own skeletons) carefully aligned into columns.

The formation as a whole allows this region to withstand a lot of pressure – much more than silicon carbide or zirconia, which are created at temperatures of 1500 degrees centigrade and used for extremely high end engineering. Behind this region are layers of chitin, each slightly rotated from the one above it (resulting in a sort of spiral structure) with the space in between the layers filled with minerals. The entire structure is designed to stop cracks from growing. Its possible that in the future things like body armour might be made with designs inspired by the mantis shrimp, which might make the eventual war against the Shrimp-Men more winnable.

Unlike most of the Mantis Shrimp featured here, Lysiosquilla tredecimdentata is both sensibly coloured and a ‘Spearer’. (Image via Wikimedia Commons)

And that’s before we start to talk about their eyes; which many people tend to understandably overlook in favour of the whole ‘superstrong punch’ thing.

They have 16 types of photoreceptor in their eyes (as opposed to our four – the three times of ‘cones’ which sense colour and the ‘rods’ that merely sense the presence or absence of light). What’s more, they have transparent filters in front of their eyes, meaning that different optical cells, containing the same type of visual pigment*, are fine tuned to different wavelengths of light – which, by the way, includes ultra-violet light, which humans can’t see.

Seeing in the UV range of the spectrum certainly comes in handy for the Mantis Shrimp – whilst the brightly coloured prey might be hard to see amidst the brightly coloured coral, many animals (not just British people on holiday) absorb UV – thus, they’d show up a nice, clear black against the brightly coloured background.

Even stranger is the fact that the filters sometimes vary in composition, so different Mantis Shrimp have different sensitivities to different wavelengths of light. Long wavelengths of light (which have weaker energy) are weakened more by water than shorter wavelengths – almost no red light, for instance, penetrates far into the sea. So, if you wanted to make your vision the best it can possibly be, you’d want to be more sensitive to red light in shallower water, and more sensitive to shorter wavelengths deeper down. However, what if you, like Haptosquilla trispinosa, live at a range of depths? In the case of this shrimp, the filters actually change depending on what the light was like during infancy – so if you were raised in light levels similar to that of shallow waters, you’ll grow up with filters suitable for shallow water, and vice versa. At this point, the fact that Mantis Shrimp can detect the polarisation (the direction on which light waves vibrate – e.g. up-to-down or side-to-side) of light comes as no surprise – but not only can they detect linear polarisation, like most crustaceans, they can detect circular polarisation as well.

Being able to detect the polarisation of light is likely to be helpful to the Mantis Shrimp, since some of its prey may either reflect light, or be transparent, (very hard to see in any case) but will change the polarisation of light, making themselves visible and vulnerable to a sudden strike. Since cancerous tumours reflect polarised light differently from healthy tissue, there’s talk of examining their eyes in much more detail to try and inspire a camera that could quickly detect cancer.

And if ou looked as awesome as this shrimp, you’d want super vision too, just to make for more efficient self-admiration. (via http://www.factzoo.com)

About the only consolation is that the Mantis Shrimp, despite having 12 photo-receptors geared to detect colour, compared to our measly 3, they don’t see a whole rainbow of colours that we cannot. Rather, it appears that each photoreceptor is specialised to detect a specific colour, but their brain is rather less efficicient than ours at combining information from different colour receptors to form an overall colour – which makes sense, given that their brains are a fraction of the size of ours.

And just to top it all off, they look amazing.

Creationists maintain Mantis Shrimps evolved during the 60s, a theory yet to be utterly disproved. (Image via http://www.aqua.org)/

* The literature appears slightly conflicted; this source states Mantis Shrimp have 16 photoreceptors, of which six detect UV but due to filters some photoreceptors use the same visual pigment, whilst this older paper simply states Mantis Shrimp have up to 16 visual pigments. This source says that mantis shrimp have 12 colour photoreceptors. Since 12 + 6 doesn’t give 16, its possible that either different species have different configurations of photoreceptors, or that there is overlap (e.g. some of the photoreceptors can detect both UV and colour) – Ed.

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