Mantis shrimp, or stomatopods, are carnivorous marine crustaceans of the order Stomatopoda, which branched off from other members of the class Malacostraca about 340 million years ago
The shell of the mantis shrimp (the hard, thick shell that covers crustaceans and other species) covers only the back of the head and the first four segments of the thorax. Varieties vary in color, from shades of brown to bright colors, and more than 450 species of mantis shrimp are known
They are among the most important predators in many shallow, tropical and subtropical marine habitats. However, despite being common, they are little known, as many species spend most of their lives hiding in burrows and holes.
Called “sea lobsters” by the ancient Assyrians,“prawn killers” in Australia, and now sometimes referred to as “thumb breakers”-because of the animal’s ability to inflict painful wounds if handled incautiously, mantis shrimp have powerful raptorials that they use to attack and kill their prey, either by lancing, stunning, or dismembering them
Some species of mantis shrimp have specialized calcified“clubs” that can strike with great power, while others have sharp forelimbs that are used to grab prey (hence the term “mantis” in their common name).
Characteristics of the Mantis Shrimp
Claws
The second pair of thoracic appendages of the mantis shrimp is highly adapted for close-range combat
Differences in appendages divide mantis shrimp into two main types: those that hunt by impaling their prey with spear-like structures and those that crush their prey with a powerful blow from a highly mineralized club-like appendage
Upon impact, these robust hammer-like claws can inflict considerable damage. This club is further divided into three subregions: the impact region, the periodic region and the striated region. Mantis shrimp are commonly divided into many (most are divided into harpoons and crushers, but there are some that are not) distinct groups determined by the type of claws they possess:
Crushers possess a much more developed club and a more rudimentary spear (which, however, is quite sharp and is still used in fights among their own kind); the club is used to bludgeon and smash their meals. The inner aspect of the terminal part of the appendix may also have a sharp edge, which is used to cut the prey while the mantis shrimp swims.
Harpoons are armed with spiny, barbed-tipped appendages, which they use to stab and hook their prey.
Both types attack by rapidly deploying and swinging their raptor claws against prey, and can inflict serious damage on victims considerably larger than their own size. In crushers, these two weapons are employed with blinding speed, with acceleration of 10,400 g (102,000 m/s2 or 335,000 ft/s2) and speeds of 23 m/s (83 km/h; 51 mph) from a starting position.
Because they strike so rapidly, they generate vapor-filled bubbles in the water between the appendage and the striking surface, known as cavitation bubbles. The collapse of these cavitation bubbles produces measurable forces on their prey, in addition to the instantaneous forces of 1,500 newtons that are caused by the impact of the appendage against the striking surface, meaning that the prey is struck twice by a single blow; first by the claw and then by the collapse of the cavitation bubbles that immediately follow
Even if the initial strike misses the prey, the resulting shockwave can be enough to stun or kill.
Crushers use this ability to attack crabs, snails, oysters and other mollusks, as their blunt sticks allow them to break the shells of their prey into pieces. Harpooners, however, prefer the flesh of softer animals, such as fish, which their barbed claws can more easily cut and hook.
These appendages are being studied as a microscale analog for new macroscale material structures.
Axe: A primitive appendage that only a few species have this body plan and are largely unresearched.
Spiked breakers (hammers or primitive breakers): possibly the “missing link” to relate the two most common (spear and breaker) to each other. Very rare and even less studied than the axe type.
Eyes
Mantis shrimp eyes are mounted on movable stalks and can move independently of each other. They are believed to have the most complex eyes in the animal kingdom and possess the most complex front part of any visual system ever discovered
Compared to the three types of photoreceptor cells that humans possess in their eyes, the eyes of a mantis shrimp have between 12 and 16 types of photoreceptor cells. In addition, some of these shrimp can tune the sensitivity of their long-wavelength color vision to adapt to their environment
This phenomenon, called “spectral tuning,” is species-specific
Despite the impressive range of wavelengths that mantis shrimp have the ability to see, they do not have the ability to discriminate wavelengths that are less than 25 nm away. It is suggested that not discriminating between nearby wavelengths allows these organisms to make determinations of their environment with little processing delay
Having little delay in assessing the environment is important for mantis shrimp, as they are territorial and are frequently engaged in combat.
Each compound eye consists of tens of thousands of ommatidia, clusters of photoreceptor cells Each eye consists of two flattened hemispheres separated by parallel rows of specialized ommatidia, collectively referred to as the median band
The number of rows of ommatidia in the median band ranges from two to six, dividing the eye into three regions. This configuration allows the mantis shrimp to see objects with three parts of the same eye. In other words, each eye possesses trinocular vision and thus depth perception. The upper and lower hemispheres are used primarily for shape and motion recognition, like the eyes of many other crustaceans.
Mantis shrimp can perceive wavelengths of light ranging from deep ultraviolet (300 nm) to far red (720 nm) and polarized light.
It is unclear what advantage polarization sensitivity confers; however, polarization vision is used by other animals for sexual signaling and secret communication that avoids the attention of predators. This mechanism could provide an evolutionary advantage; it requires only small changes in the eye cell and could easily result in natural selection.
The eyes of mantis shrimp may allow them to recognize different types of coral, prey species (which are usually transparent or semitransparent) or predators, such as the barracuda, which has shiny scales. On the other hand, the way they hunt (very fast claw movements) may require very precise range information, which would require accurate depth perception.
During mating rituals, mantis shrimp actively emit fluorescence, and the wavelength of this fluorescence matches the wavelengths detected by the pigments in their eyes. Females are only fertile during certain phases of the tidal cycle; the ability to sense the phase of the moon may therefore help prevent wasted mating efforts. It may also give these shrimp information about the size of the tide, which is important for species that live in shallow water close to shore.
The ability to see ultraviolet light may allow observation of prey that would otherwise be difficult to detect on coral reefs.
Where does the Mantis crab live?
Some 450 species of mantis shrimp have been discovered worldwide; all living species belong to the suborder Unipeltata, which arose about 193 million years ago.
These aggressive and typically solitary marine creatures spend most of their time hiding in rock formations or digging intricate passages in the seafloor. They rarely leave their homes, except to feed and relocate, and may be active during the day, nocturnal or crepuscular (active at twilight), depending on the species
Unlike most crustaceans, they sometimes hunt, pursue and kill their prey. Although some live in temperate seas, most species live in tropical and subtropical waters of the Indian and Pacific Oceans, between East Africa and Hawaii.
Mantis shrimp live in burrows where they spend most of their time. The two categories of mantis shrimp -throwers and crushers- prefer different places to make their burrows
Thrower species build their habitat in soft sediments and crusher species make their burrows in hard substrates or coral cavities. These two habitats are crucial to their ecology, as they use burrows as places of refuge and to consume their prey
Burrows and coral cavities are also used as places for mating and to keep their eggs safe. Stomatopod body size undergoes periodic growth, making it necessary to find a new cavity or burrow to fit the animal’s new diameter. Some harpoon species can modify their pre-established habitat if the burrow is made of silt or mud, which can be enlarged.
Habits and behaviors
Mantis shrimp are long-lived and exhibit complex behaviors, such as ritual fights. Some species use fluorescent patterns on their bodies to signal with their own and perhaps other species, expanding their range of behavioral signals.
They can learn and remember well, and are able to recognize individual neighbors with whom they interact frequently. They can recognize them by visual cues and even by individual scent. Many have developed complex social behaviors to defend their space from rivals.
Over their lifetime, they may have as many as 20 to 30 breeding episodes. Depending on the species, eggs may be laid and kept in a burrow, or they may be carried under the female’s tail until they hatch. Also depending on the species, males and females may come together only to mate, or they may join in long-term monogamous relationships.
In monogamous species, mantis shrimp remain with the same partner for up to 20 years. They share the same burrow and can coordinate their activities. Both sexes usually care for the eggs (biparental care)
Captive breeding
Some saltwater aquarists keep stomatopods in captivity. The peacock mantis is especially colorful and desired in the trade.
While some aquarists value mantis shrimp, others consider them detrimental pests, because they are voracious predators, eating other desirable aquarium inhabitants. In addition, some rock-eating species may do more damage to live rock than the aquarist would prefer.
Live rock with mantis shrimp burrows is considered useful by some in the marine aquarium trade and is often collected. It is not uncommon for a piece of live rock to transport a live mantis shrimp into an aquarium. Once inside the aquarium, it may feed on fish and other inhabitants, and is notoriously difficult to catch when it becomes established in a well-stocked aquarium
Although there are accounts of this shrimp breaking glass tanks, they are rare and are usually the result of the shrimp being kept in too small a tank. Although stomatopods do not eat coral, crushers can damage it if they try to make a home in it.
