mantis shrimps and Circular Polarized Light

ETA October 27, 2009: Latest article on the shrimps from Sci Am Online:

…Unlike linearly polarized light, in which the electric field oscillates along a plane, circularly polarized light’s field twists like a spiral spring as the ray propagates. Such light is not commonly reflected from animal bodies and so was long dismissed as a virtual nonfactor in physiology, but research last year showed that some stomatopods have the ability to discriminate circular polarization. A paper published online October 25 in Nature Photonics unpacks the mechanism behind the mantis shrimp’s ability and concludes that its eyes handle circularly polarized light more effectively than man-made optical devices do…

…But the creature is physiologically remarkable in at least one other way: The compound eye of the peacock mantis, the new study’s authors found, harbors a natural quarter-wave retarder, a sort of filter that converts circularly polarized light to linearly polarized light, which then activates receptors below. “Biologically, this is unique,” says study co-author Thomas Cronin, a professor of biological sciences at the University of Maryland, Baltimore County. “There is nothing else known anywhere in biology” that enables detection of circularly polarized light, he adds….

…The stomatopods reflect circularly polarized light from their bodies, so their ability to detect such light—and to parse clockwise from counterclockwise polarization—likely plays a role in signaling or identification. In some stomatopod species, reflection of circularly polarized light is sex-specific, which could play a role in sexual signaling or mate selection.

Wave retarders work by refracting light differently depending on the angle of its polarization, delaying one wave component of a light wave relative to the other. “If it’s just the right degree of delay, which is one-quarter wave or 90 degrees phase, that converts circularly polarized light to linearly polarized,” Cronin explains. But unlike wave retarders available commercially, which are tuned for specific wavelengths (and hence colors) of visible light, the wave plate in the O. scyllarus eye performs almost identically across the visible spectrum.

The mantis shrimp’s eye, Cronin explains, “works on a principle that is not used currently but could be used in manufacturing systems”—balancing the optical properties of the eye structure with those of the lipid molecules that fill the structure. “The two have different wavelength functions—they have different curves of changing retardance with wavelength—and so the animal trades them off,” Cronin says. “It trades off structure against material to cancel out the two variations.”…


Link that Kiya came up with, very cool ideas for how Dance may be generating/sensing polarized light.

Coiled ribbon sensors might be antennas capable of picking up CPL.

Mantis shrimps have th ability to pick up on circular polarized light (CPL), which no other animal on earth does.

They’ve evolved on their own since the Cretaceous, and they’re pretty damn strange in their own right. They also used to be the recordkeeper on fastest-moving animal reactions. Also interesting!

Also gorgeously colorful animals for a tropical saltwater aquarium, but they’re pretty large animals, which puts a strain on a system. Peacock mantis shrimps are popular, they can be 4” long. That’s big for an animal you keep in a burrow by itself. Oh yeah. No other mantis shrimps in there, very territorial. If it’s a spearing type? No fish. A hammer type? No shrimps, clams, etc.

Another article, from Wired about the same time in 2009 discusses the same technical possibilities from studying the eyes.

There’s a lot of videos of mantis shrimps online, moving around, attacking things like crabs, and many of the vids include the pistol-shrimp noise that the striking arms give. Some of the better-shot vids make it clear these are not merciful critters, they almost seem like they’re playing with their food.

Every vid that I looked at showed a totally different species. They all had a slightly different body shape and coloration, but they look sort of like a shrimp-centaur. Add a lobster-like heavy thorax with these weird round sensor-flaps at the front end of a long shrimp.

They are all alert, active predators. They don’t get the job done on a crab in one blow, and the crabs can hurt them back. But they keep coming at the poor crab. You’re warned: It’s kind of disturbing to watch, the crab doesn’t have a prayer.

I would say, shrimp is to mantis shrimp as snake is to dragon.
From Wired magazine online:


More elaborate information on the visual processing and eye structures can be found in Wikipedia:


…As became clear when Cronin finished explaining CPL and started talking about the animal, what gets these guys to the lab in the morning is the mantis shrimp itself.

“They’re enchantingly violent,” he said in an affectionate, almost paternal tone. “They catch other animals by either spearing it through the heart or smashing it to pieces. Unlike most predators that grab prey, these pummel it and destroy it. When they interact with each other over a burrow, they use their armored front appendages and smash each other on the face. Whenever they get into any type of situation, they smash things. You can’t pick these up. They’re really great animals to have around.”

Cronin seemed especially pleased that the shrimps’ visual uniqueness would return them to the record books. “The movement they use to hit prey used to be the fastest movement made by any animal,” he lamented. “But it turned out there was a jaw-snapping behavior in an ant that’s even faster.”…

…Cronin noted that some species have a CPL-reflecting patch on their tail, which they use to signal each other while negotiating mates or territory — but there are plenty of other ways to do this. Then again, when you and your possible opponent are so fundamentally bash-inclined, it makes sense to keep every possible communication channel open.

And channels the mantis shrimp has in abundance. Though CPL-sight is their greatest claim to optical fame, their eyes are chock full of weird cells and structures that let them distinguish between no fewer than 100,000 colors — ten times more colors than we can see…

So why do mantis shrimp — which followed a solitary evolutionary trajectory out of the Cambrian, developing a physiology so weird that scientists called them “shrimps from Mars” — have such marvelous eyesight?

“One idea is that the more complicated your sensory structure is, the simpler your brain can be,” said Cronin. “If you can deal with analysis at the receptor level, you don’t have to deal with that in the brain itself.”

There you have it: the world’s most sensitive eyes allow them to be simple! And smash things! And it’s worked for 400 million years…

More on the shrimp’s vision in another Wired article here:

peacock mantis shrimp
one of the prettier mantis shrimp


Like insects and other crustaceans, mantis shrimps possess compound eyes composed of thousands of rows of light-detecting units called ommatidia. These are especially refined in mantis shrimps, containing a mix of photoreceptors and filters that let them see 100,000 different colors — 10 times more than can be detected by humans.

Two decades ago, Cronin, along with co-authors Justin Marshall at the University of Queensland and the University of California, Berkeley’s Roy Caldwell, noticed that sections of the mantis shrimps’ ommatidia are arranged at a slant.

This suggested an ability to detect circular polarized light, in which photons follow a corkscrew path and ostensibly enter the ommatidia at a correspondingly slanted angle. After finding a species that seemed to send signals with a CPL-reflecting patch of exoskeleton, the researchers decided to test whether the shrimps’ oddball ommatidia really registered the light.

First they hooked severed eyes to electrodes to measure whether the cells energized when hit with circularly polarized light; they did. Then they trained the shrimps to associate CPL-reflecting boxes with food. The shrimps passed the test with flying colors.

Cronin said the shrimps probably use CPL to communicate during sexual and territorial encounters, though he doesn’t know why they evolved such a one-of-a-kind system. Further research may illuminate those origins — and, Cronin said, could help scientists refine their use of CPL in computer screens and signal transmission, where its tightly rotating configuration lends itself to loss-free transmission….

More elaborate information on the visual processing and eye structures can be found in Wikipedia:

Squilla mantis, showing the spearing appendages:

Both types strike by rapidly unfolding and swinging their raptorial claws at the prey, and are capable of inflicting serious damage on victims significantly greater in size than themselves. In smashers, these two weapons are employed with blinding quickness, with an acceleration of 10,400 g and speeds of 23 m/s from a standing start [6], about the acceleration of a .22 caliber bullet. Because they strike so rapidly, they generate cavitation bubbles between the appendage and the striking surface [6]. The collapse of these cavitation bubbles produces measurable forces on their prey in addition to the instantaneous forces of 1,500 N that are caused by the impact of the appendage against the striking surface, which means that the prey is hit twice by a single strike; first by the claw and then by the collapsing cavitation bubbles that immediately follow [7]. Even if the initial strike misses the prey, the resulting shock wave can be enough to kill or stun the prey.

The snap can also produce sonoluminescence from the collapsing bubble. This will produce a very small amount of light and high temperatures in the range of several thousand Kelvin within the collapsing bubble, although both the light and high temperatures are too weak and short-lived to be detected without advanced scientific equipment. The light emission and temperature increase probably have no biological significance but are rather side-effects of the rapid snapping motion. Pistol shrimp produce this effect in a very similar manner.

Smashers use this ability to attack snails, crabs, molluscs and rock oysters; their blunt clubs enabling them to crack the shells of their prey into pieces. Spearers, on the other hand, prefer the meat of softer animals, like fish, which their barbed claws can more easily slice and snag.

…Some species have at least 16 different photoreceptor types, which are divided into four classes (their spectral sensitivity is further tuned by colour filters in the retinas), 12 of them for colour analysis in the different wavelengths (including four which are sensitive to ultraviolet light) and four of them for analysing polarised light. By comparison, humans have only four visual pigments. The visual information leaving the retina seems to be processed into numerous parallel data streams leading into the central nervous system, greatly reducing the analytical requirements at higher levels.

One species has been reported to be able to detect circular polarized light

I would say, shrimp is to mantis shrimp as snake is to dragon.

Close-up of Pseudosquilla ciliata’s trinocular vision

Reasons given for powerful eyesight

The eyes of mantis shrimp may make them able to recognise different types of coral, prey species (which are often transparent or semi-transparent), or predators, such as barracuda, which have shimmering scales. Alternatively, the manner in which mantis shrimp hunt (very rapid movements of the claws) may require very accurate ranging information, which would require accurate depth perception.

The fact that those with the most advanced vision also are the species with the most colourful bodies, suggests the colour vision has taken the same direction as the peacock‘s tail.

During mating rituals, mantis shrimp actively fluoresce, and the wavelength of this fluorescence was shown to match the wavelengths detected by their eye pigments [2]. Females are only fertile during certain phases of the tidal cycle; the ability to perceive the phase of the moon may therefore help prevent wasted mating efforts. It may also give mantis shrimp information about the size of the tide, which is important for species living in shallow water near the shore.

Another theory is that the invertebrate brain is unequipped to analyse all the incoming data in real time and so the processing is performed physically by the eye…


…Mantis shrimp appear to be highly intelligent, are long-lived and exhibit complex behaviour, such as ritualised fighting. Scientists have discovered that some species use fluorescent patterns on their bodies for signaling with their own and maybe even other species, expanding their range of behavioural signals. They can learn and remember well, and are able to recognise individual neighbours with whom they frequently interact. They can recognise them by visual signs and even by individual smell. Many have developed a complex social behaviour to defend their space from rivals.

In a lifetime, they can have as many as 20 or 30 breeding episodes. Depending on the species, the eggs can be laid and kept in a burrow, or carried around under the female’s tail until they hatch. Also depending on the species, male and female come together only to mate or bond in monogamous long-term relationships.

In the monogamous species, the mantis shrimp remain with the same partner for up to 20 years. They share the same burrow, and there are reasons to suspect that these pairs can coordinate their activities. Both sexes often take care of the eggs (biparental care). In Pullosquilla and some species in Nannosquilla, the female will lay two clutches of eggs, one that the male tends and one that the female tends. In other species, the female will look after the eggs while the male hunts for both of them. Once the eggs hatch the offspring may spend up to three months as plankton…

…Many saltwater aquarists keep stomatopods in captivity. These aquarists may play a role in understanding the mysteries of the mantis shrimp. However, mantis shrimp are considered pests by other hobbyists because they can be transported unwittingly in a load of rocks destined for an aquarium. Once inside the tank, they may feed on fish, corals, and smaller crustaceans. They are notoriously difficult to catch when established in a well-stocked tank, and although there are accounts of them breaking and destroying glass tanks, such incidents are very rare…

An article on the mechanism of the smashing claw:

The mantis shrimp – the world’s fastest punch

… Mantis shrimps are aggressive relatives of crabs and lobsters and prey upon other animals by crippling them with devastating jabs. Their secret weapons are a pair of hinged arms folded away under their head, which they can unfurl at incredible speeds.
The ‘spearer’ species have arms ending in a fiendish barbed spike that they use to impale soft-bodied prey like fish. But the larger ‘smasher’ species have arms ending in heavy clubs, and use them to deliver blows with the same force as a rifle bullet.

Fastest claw in the west

mantis shrimp claw
fastest claw in the west

When Sheila Patek, a researcher at USC Berkeley, tried to study these heavy-hitters on video, she hit a snag. “None of our high speed video systems were fast enough to capture the movement accurately” she explained.
“Luckily, a BBC crew offered to rent us a super high speed camera as part of their series ‘Animal Camera’.” (Photograph above by Sheila Patek & Wyatt Korff)
With this cutting-edge equipment, Patek managed to capture footage of a smasher’s strike, slowed down over 800 times. What she found was staggering. With each punch, the club’s edge travels at about 50 mph, over twice as fast as scientists had previously estimated.*
“The strike is one of the fastest limb movements in the animal kingdom”, says Patek. “It’s especially impressive considering the substantial drag imposed by water.”Water is much denser than air and even the quickest martial artist would have considerable difficulty punching in it. And yet the mantis shrimp finishes its strike in under three thousandths of a second, out-punching even its land-living namesake.

The need for speed
If the animal simply flicked its arm out, like a human, it would never achieve such blistering speeds. Instead, mantis shrimps use an ingeniously simple energy storage system. Once the arm is cocked, a ratchet locks it firmly in place. The large muscles in the upper arm then contract and build up energy. When the latch is released, all this energy is released at once and the lower arm is launched forwards.
But Patek found that even this system couldn’t account for the mantis shrimp’s speed. Instead, the key to the punch is a small, structure in the arm that looks like a saddle or a Pringle chip.
When the arm is cocked, this structure is compressed and acts like a spring, storing up even more energy. When the latch is released, the spring expands and provides extra push for the club, helping to accelerate it at up to 10,000 times the force of gravity.

This smasher’s arm is truly state-of-the-art natural technology. “Saddle-shaped springs are well-known to engineers and architects”, explains Patek, “ but is unusual in biological systems. Interestingly, a recent paper showed that a similarly shaped spring closes the Venus’s fly trap.”

Killing with bubbles
Patek’s cameras revealed an even bigger surprise – each of the smasher’s strikes produced small flashes of light upon impact. They are emitted because the club moves so quickly that it lowers the pressure of the water in front of it, causing it to boil.
This releases small bubbles which collapse when the water pressure normalises, unleashing tremendous amounts of energy. This process, called cavitation, is so destructive that it can pit the stainless steel of boat propellers. Combined with the force of the strike itself, no animal in the seas stands a chance.
Large smashers can even make meals of crabs, buckling their thick armour as easily as they do aquarium glass. And they are often seen beating up much larger fish and octopuses, which are unfortunate enough to wander past their burrows. Not just a good right hook
Some scientists think that the mantis shrimps’ belligerent nature evolved because the rock crevices they inhabit are fiercely contested. This competition has also made these animals smarter than the average shrimp. They are the only invertebrates that can recognise other individuals of their species and can remember if the outcome of a fight against a rival for up to a month….

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