The mantis shrimps are a fierce group of marine crustaceans belonging to the order Stomatopoda. Pre-dating the dinosaurs, this fascinating group of animals branched off from Malacostraca, the largest of the crustacean classes, 340 million years ago. All living species are in the suborder Unipeltata, which first arose approximately 193 million years ago.

Over 400 species of mantis shrimps have been described, each varying in size and colour. The most well-known species is the peacock mantis shrimp, Odontodactylus Scyllarus, whose dazzling colours makes it particularly desirable in the aquarium trade.

The peacock mantis shrimp, displaying its range of bright colours. Picture by Richard Whitcombe.

Typically, individuals grow to around 10 cm in length, however cases of 38 cm long mantis shrimp have been reported.

As with all crustaceans, the mantis shrimp is covered in a thick exoskeleton known as its carapace. This armour covers the rear portion of the head and the first four segments of the thorax.

The mantis shrimp plays a key role in many shallow tropical and sub-tropical habitats in the Indian and Pacific Ocean, where it acts as a predator and helps keep its ecosystem in balance. As with most apex predators, the mantis shrimp is aggressive and solitary by nature.

Most of their time is spent in their intricate burrows within the seabed; mantis shrimp will only leave their home to feed, relocate, and attract mates. Upon finding a mate the pair will share their burrow, with some species even forming monogamous bonds.

A purple spot mantis shrimp emerging from its rocky burrow. Picture by Roy Caldwell.

Despite resembling a typical shrimp, these creatures are dramatically different to their crustacean cousins and have earned themselves quite the reputation. “Prawn killers”, “thumb splitters” and “sea locusts” are just some of the names that these critters are known by.

So why the notoriety?

The Armory

All arthropods are composed of segments which can be organised into three main regions: the head, the thorax, and the abdomen. In some species, the head and thorax may fuse to form the cephalothorax which can be covered by a large single-piece carapace. Each section can bear a pair of appendages, each specialised for various activities.

For instance, a typical shrimp such as the European shrimp, Crangon crangon, has eight pairs of appendages within the cephalothorax region. The first three pairs are called maxillipeds which is Latin for “jaw feet”. As such, these appendages aid in food processing.

Next comes five more pairs of appendages, the pereiopods which form the ten decapod legs. These are the limbs that can commonly be found washed up on the beach.

The following five pairs of limbs are the pleopods, which are paddle-shaped and adapted for swimming. Finally, come the pair of uropods which are attached to the telson, the ‘tail’ of the shrimp.

The body plan of the common shrimp, Crangon crangon.

The mantis shrimp body plan does not diverge greatly from that of the typical crustacean.

However, there is one clear difference that sets them aside from all their crustacean counterparts: the possession of lethal weapons.

All species of mantis shrimp can be split into two groups: one which possesses spear-like appendages with which they stab their prey, and another which clubs their foes to death with their boxing glove-esque appendages.

The weapons of the mantis shrimp. On the left is the raptorial appendage of a spearer mantis shrimp. On the right is the raptorial appendage of a smasher mantis shrimp. Picture taken from themantisshrimp.

These weapons are the second pair of thoracic appendages and work with deadly results.

Through rapidly unfolding and swinging their raptorial claws at speeds of over 50 mph, the mantis shrimp is not limited to similar sized prey. Indeed, owing to their significant firepower, mantis shrimps can protect themselves from all manner of organisms including the notably larger California two-spot octopus.

The raw power behind the blow generates super-heated vapor-filled bubbles known as cavitation bubbles, which (for a split second) can reach temperatures of 4,400 °C. When these bubbles collapse, an intense force is exerted, and the prey is essentially hit twice in quick succession.

The power of the mantis punch has also been known to break aquarium glass and knock crab legs clean off.

The mantis shrimp packs such a punch that even humans are at risk of injury.

All of this firepower makes the mantis shrimp one of the most formidable predators in the ocean. But the incredible adaptations don’t end there. The mantis shrimp has eyes like no other.

All the Better to See You With

The mantis shrimp is widely believed to have the most complex eyes across the entire animal kingdom. As is the case with all arthropods, mantis shrimp have compound eyes, each mounted on a stalk and able to move independently of one another.

Compound eyes are made up of tens of thousands of ommatidia, each containing a cluster of photoreceptor cells which can detect light independently. The black band in the centre of the eye holds the key to the unique visual system possessed by this animal – it is where colour is detected.

The mantis shrimp compound eye. The black midband is where all colour detection takes place. Picture taken from awesci.com.

The majority of people have three types of photoreceptors, each sensitive to different waves of light – red, green, and blue. Depending on the species, mantis shrimp can have up to 16 different photoreceptors in its midband. This allows them to see an impressive range of wavelengths, from deep ultraviolet (280 – 315 nm) to far-red (700 – 800 nm) and even polarized light.

Despite the seemingly impressive visual acuity, a 2014 study led by Hanna Theon at the University of Queensland, found that mantis shrimps are far worse at discriminating between colours than most other animals.

So why the impressive hardware?

The answer is that we simply don’t know! However, the scientists behind the study have a hypothesis.

Mantis shrimps may be processing all of their visual data at once, without comparing between the receptors. By forgoing the need for brain processing, the mantis shrimp could make a rapid assessment of their environment which would assist in the high-speed hunter lifestyle that they are famous for.

A study of the same year revealed that by being able to detect polarised light, the eyes of the mantis shrimp can detect cancer as well as neuron activity. This is because polarised light reflects differently from cancerous and healthy tissues. This miraculous ability may hold immense biomedical implications – attempts at recreating the naturally occurring phenomenon have already taken place.

The Eternal Shrimp

The weird and wonderful mantis shrimp is just one of nature’s many oddities that can be found in the ocean. Thankfully, owing to their range of warrior adaptations, the mantis shrimp may not fall vulnerable to global climate change. Just as they outlived the dinosaurs; the mantis shrimp might just outlive us all.

Written by Lucas King