Mantis Shrimp (Order Stomatopoda)
The rapacious rainbow shrimp with a rapid right hook
Part of the order Stomatopoda, mantis shrimp are carnivorous marine crustaceans that prowl the tropical and sub-tropical waters of the Indian and Pacific oceans. Genetic sampling of modern and museum species revealed that this family of shrimp branched away from the rest of the class Malacostraca, a diverse group of crustaceans including lobsters, crabs, crayfish, shrimp and krill around 340 million years ago, developing the specialised smashing claw that gives them such a fearsome reputation.
Often called ‘thumb-splitters’ thanks to their ability to give any careless human a nasty injury, mantis shrimp have specially evolved appendages that they use to attack and kill prey through stunning, spearing or dismembering. All 450 species of mantis shrimp can be divided into two groups based on their murderous modus operandi; ‘spearers’ or ‘smashers’. Spearers have spiny appendages that they use to stab soft bodied prey, like marine worms and small fish. In contrast smashers have more club like appendages, used to bludgeon and quite literally punch their prey into pieces. Smashers are arguably the most impressive; they have been recorded using these raptorial appendages at the front of their bodies to smash prey at over 50 miles per hour, delivering a force of 1500 newtons, the same velocity as a .22 caliber bullet being fired from a gun. This punch is so fast, it results in something called ‘cavitation bubbles’; super-heated bubbles and a brief flash of light which for a split-second heats the water to 4400oC (close to the temperature of the sun!).
Peacock mantis shrimp, one of the brightest and most colourful species are particularly sought after in the aquarium industry. However, you have to be prepared to take on one of these feisty little shrimps, as they have been known to punch through aquarium glass when they attack their own reflection. If they come across an obstacle in their way, they’re likely to punch through, so you might come back and find your carefully arranged tank decorations are not in the state you left them.
How can such small creatures punch so hard without injuring themselves in the process? Their super charged clubs have a layer of elastic polysaccharide chitin, a fibrous substance found in fungal cell walls and the exoskeletons of invertebrates. In the mantis shrimp these chitin layers are arranged in such a way that they prevent cracks in one layer becoming a full break of the whole structure. This is such an effective mechanism that researchers are looking to these specialised clubs to develop better impact resistant material for body armour, car frames and aircraft panels.
All the better to see you with: the amazing eyes of the mantis shrimp
Mantis shrimp have one of the most advanced visual systems in the animal kingdom. Their eyes are mounted on stalks and can move independently of each other, allowing the shrimp to have a wide visual field. They have up to 16 classes of photoreceptor, in contrast to the three humans have; red, blue and green. Mantis shrimp can see UV, visible and polarised light and are the only animals known to perceive circularly polarised light, which is a wave component of light that moves in a circular motion.
Certain species of shrimp can tune their eyesight to different wavelengths depending on their environment. This incredible eyesight has even been shown by researchers from the University of Queensland to be able to detect cancer cells before they develop into tumours, as cancerous cells deflect light differently than healthy tissues. This inspired researchers to develop a specialised camera based off their visual system to detect cancer cells before they form a tumour.
How this super advanced vision benefits the mantis shrimp is not entirely known, but its likely related to their lightning-fast punches requiring them to have very accurate depth and range perception. Mantis shrimp also fluoresce during mating rituals and as females are only fertile during the tidal cycle, the complex pigments in their eyes may enable them to determine reproductive states and therefore prevent them wasting their time wooing a girlfriend when they could be punching crabs to death for their dinner.
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Franklin, A.M. (2013) ‘Mantis shrimp have the world’s best eyes-but why?’
Han, Q. Shi, S. Liu, Z. Han, Z. Niu, S. Zhang, J. Qin, Y. and Wang, J. (2020) ‘Study on impact resistance behaviours of a novel composite laminate with basalt fiber for helical-sinusoidal bionic structure of dactyl club of mantis shrimp.’ Composites Part B: Engineering.
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