Nature and Science
Author: Fredy Brauchli
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Peacock Mantis Shrimps – Pugnacious Predators
Mantis shrimp can kill their prey within milliseconds. They have sensational, compound eyes mounted on mobile stalks.
They receive their common name mantis shrimp from the physical resemblance to both the terrestrial praying mantis and the shrimp. In science, the order is referred to as Stomatopoda (from the Greek words “stoma”= mouth, and "podus"= foot). Stomatopoda belong to the class of Malacostracae and comprise around 400 species, with the Peacock Mantis Shrimp, also called Harlequin or Colored Mantis Shrimp, being the most famous species.
Why Mantis Shrimp are Special
Mantis shrimp mainly live in the coastal regions of tropical and subtropical seas, either inhabiting bottom burrows or crevices in coral rock or digging their own caves in the sand. They range in size from around 1 cm to more than 35 cm. The long and narrow body of the mantis shrimp comprises an articulated abdomen with a strong fantail ending in a telson with paired uropods. The first pair of appendages is used as a cleaning organ. The second pair of very powerful appendages is armed with a row of spines or a massive club; then follow three pairs of appendages used to hold the prey. These five pairs of thorax appendages in total are protected by the flat carapace. The remaining three pairs of walking legs (pereopods), five pairs of swimmerets (pleopods) and the telson form the long abdomen of the mantis shrimp. Stomatopods possess exceptionally large compound eyes, mounted on stalks. The group can be divided functionally into two groups: the smashers and the spearers.
Highly Developed Compound Eyes
Stomatopods possess the most highly developed eyes of all crustaceans. Each movable compound eye is made up of up to 10.000 high-resolution photoreceptor cells. The midband divides the eye into three regions. This design makes it possible for the mantis shrimp to see each object from three different parts of the eye. Two analyzers help the animal to locate the prey, to exactly determine the distance and to strike it most effectively. According to Debelius, most spearers are active at night lurking for their prey. They have no color vision but are able to see even at minimum light. Smashers, on the contrary, are active at day and have at least 10 photoreceptor types (compared to 3 in humans), further tuned by several color filters, which give them a highly differentiated vision.
Fast as Lightning
While spearers use their spiny appendages topped with barbed tips to ‘spear’ prey, smashers ‘smash’ their meal using their heavily calcified clubs. Both actions happen with lightning speed, i.e. in around 3 milliseconds. This acceleration of 100m/sec generates tiny cavitation bubbles, which are then collapsing. The collapse produces forces that are strong enough to numb the prey or even smash their carapace.
Behavior and Intelligence
Stomatopods appear to be intelligent and exhibit complex behavior, such as using fluorescent patterns on their body and processes at their head for communication. Their very advanced social behavior can be recognized in their territorial fighting. And they have an excellent memory capacity. According to some Aquarians, mantis shrimps are able to recognize the face of a keeper even years later, and are able learn tricks.
The night-active spearer wait in their cave, luring for the prey and strike lightning-fast, by spearing soft-body animals, like fish, shrimps and cephalopods with their raptorial claw from below. By contrast, smashers go hunting during the day. They usually feed on hard-body animals, such as hermit crabs, clams, sea slugs and shrimps. Smashers have a heavily calcified claw shaped like a club, which they use to smash and hammer their prey. Their ability to exactly determine distances is crucial for their success in their hunt.
A Little Warning
To conclude, we would like to warn divers looking for great shots to hassle the Peacock Mantis Shrimps. When threatened, they may well use their raptorial claw for defense. And they can easily smash the front glass of the underwater camera or break one of the diver’s fingers.