The researchers demonstrated that larvae of the Philippine mantis shrimp can execute ultra-fast movements when they are no larger than a short grain of rice.
The punching appendages, which measure less than ome millimeter, develop right as the larva exhausts its yolk reserves, moves away from its nest, and heads out into the ocean. At this point, the baby shrimp immediately begin preying on organisms smaller than a grain of sand.
The larvae are slower than the adults, even though the young mantis shrimp can accelerate its arms almost 100 times faster than a Formula One car.
“They’re producing amazing speeds and impressive accelerations relative to their body size, but they’re not as fast as adults,” said study lead author Jacob Harrison.
The remarkably fast speeds of mantis shrimp are achieved using a tiny spring-actuated mechanism hidden in their punching appendage.
According to the researchers, when a muscle contracts, a tiny segment of their exoskeleton is deformed, and elastic energy is stored in the locked joint. When the latch releases, and the exoskeleton springs back into its natural position, the appendage is propelled forward with ultra-fast speeds.
Adult mantis shrimps have opaque exoskeletons, which makes it impossible to observe their spring-latch mechanisms in action. On the other hand, the exoskeleton of larvae is much thinner and fully transparent. Simply by watching them under a microscope, the researchers could see precisely how the larvae manage to store so much elastic energy in their tiny appendages.
“One of the trickiest parts of researching spring-actuated mechanisms is that a lot of those elements are working inside the animal. We can look outside of the animal and see the behavior, measure the kinematics, dissect the animal, and say the mechanism looks like it works like this, but there are always levels of assumption,” said Harrison.
“Transparency sets up larval mantis shrimps as systems where we can look at how each of these elements work in concert together, It removes assumptions and allows us to understand it on a finer scale.”
The study is published in the Journal of Experimental Biology.