News / Species Spotlight / Revisited: Mantis Shrimp (05/21/15)

Revisited: Mantis Shrimp



by Charles J. Hanley III

Scientific Name: Numerous
Common Name: Mantis Shrimp

Taxonomy:

Domain: Eukarya
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Crustacea
Class: Malacastraca
Super Order: Hoplocarida
Order: Stomatapoda
Families: Squillidae, Lysiosquillidae, Gonodactylidae, and Bathysquillidae
Genera: Numerous
Species: Numerous



Description:

Many aquarium animals have impressive reputations, but few can live up to that of the mantis shrimp. These tough crustaceans are often described as violent, aggressive killers that will also break glass tanks and split open fingers. At the same time, mantis shrimp are known to be intelligent and personable!

Mantis shrimp have highly advanced eyes, ferociously fast arms used to club, slash, or stab prey (and other things!), and relatively robust rear ends that some people find delectable when served with french fries.

To start, mantis shrimp are not even shrimp. In fact, they are not even in the same order, nor the same super order as shrimps. Mantis shrimp, like all crustaceans, are of the subphylum Crustacea. And like crab, shrimp, and lobster, they also belong to Class Malacastraca. They diverge at the next level, that of Super Order. Crabs, shrimp, and lobsters all share the super order Decapoda. Mantis shrimp, on the other hand, command a Super Order all their own, known as Hoplocarida (greek for Spear Carrying Soldier Shrimp). Though other orders have existed during the 400 million year old lineage of these animals, their only extant order is known as Stomatapoda. Mantis shrimp are further subdivided into four distinct families called Squillidae, Lysiosquillidae, Gonodactylidae, and Bathysquillidae. Recognizing the complexity of this taxonomy is important, but henceforth in this article it will be convenient to refer to mantis shrimp as stomatopods.

Stomatapods resemble shrimp in a way, but they also look a praying mantis insect smooshed together with a lobster, and sporting an aliens head. In truth, there is a lot that goes in to the description of an arthropods anatomy, and it is all about the number and placement body segments, appendages, and joints. Fortunately, what you need to know about stomatapods comes down to the details of just one part. The weapon arms of these animals are usually described as raptorial appendages, although they are really highly specialized maxillipeds. The raptorial appendage comes in one of two varieties, smasher or spearer, and each has its own deadly adaptation. Both styles are sub-chelate, which means that the last segment on the arm folds flat against its neighbor like a switch-blade knife. One type of appendage flicks out with a scythe-like blade that includes numerous sharp spines, emerging in a plane from the inside edge of the blade. The primary use of this variety of raptorial appendage is as a slashing or stabbing weapon. The other form of weapon is used for clubbing and smashing, as evident from the thickened basal end of the segment, and the tendency for the stomatapod to keep it folded during use. Nonetheless, the segment still carries a thin, sharp spine that can be unfolded and used for stabbing.

The raptorial appendages are interesting, not just for their power, but also because of their speed. It has been stated, though probably not definitively proven, that the strike of a mantis shrimp is one of the fastest movements in nature. The animals can lash out with a force comparable to that of a small-caliber bullet, and the event unfolds in less than 25 one-thousandths of a second! They are reported to shatter the sides and bottoms of glass aquaria, and more than one careless aquarist has fallen victim to a seriously cut-up finger from the attack of this miniature heavyweight. The combination of speed and power allows mantis shrimp to catch fish and smash through the shells of hermit crabs and crabs. It also enables them to enlarge the rocky holes they sometimes inhabit, defend themselves from predators, and burrow into soft substrates. In fact, the shape of the raptorial appendage provides an insight into the preferred habitat of a stomatapod. Smashers tend to live in rocky holes or rubble piles, and they can be heard doing nighttime demolition work on their lairs. Smashers are regularly imported into aquariums as hitchhikers riding live rock. Spearers, on the other hand, prefer to live in burrows made in soft substrate. For this reason, spearers are not often encountered in the aquarium trade, though some varieties are sold as market food.


Ecology:

Sometimes ecology is a tough subject to discuss when referring to a single taxonomic subject. Fortunately, stomatapods have one characteristic that sets them apart from every other organism on Earththey are considered to have the most complex eyes in nature. They also have cells in their eyes that enable them to see twelve distinct colors, as opposed to our own three. Whereas humans can only distinguish between about 10,000 color combinations, mantis shrimp are able to see over 100,000! Stomatapods, like many marine invertebrates, have their own built in pair of fishing lens, meaning that they can see linearly polarized light. More significantly, they are the only species of any kind that have ever demonstrated the ability to see Circular Polarized Light (CPL). This unusual type of light spirals outward from its source, and either spins to the left or to the right. Researchers have actually used the handedness of the light to prove that mantis shrimp can both see it, and learn to associate it with rewards.

Because of the unique nature of this type of vision, relatively little is known about its uses. However, researchers have postulated that is relates to sexual reproduction. Studies have shown that the carapaces of male stomatapods reflect CPL while the females do not. Moreover, different species reflect the light differently, leading to the belief that the ability to see CPL is used to detect potential mates. In addition, predators cannot see CPL, so stomatapods can communicate with one another while remaining invisible to dangers. It has also been suggested that the prey species may be more clearly visible when viewed through CPL, which is supported by evidence that mantis shrimp have exceptional
depth perception.

Another interesting fact about stomatapod vision is that it is superior to artificial technologies designed to perform similar functions. For example, CDs and DVDs utilize both linear and circular polarized light. Stomatopods are able to see these types of light waves throughout the entire visible light spectrum. Unfortunately, CDs and DVDs can only function in a narrow band of this same spectrum. In the future, researchers may use stomatapods eyes as a model for new advances in optics.


Aquarium Care:

In consideration of their fearsome reputation, it is no surprise that much of the mantis shrimp husbandry information details how to remove them from a system. Though doing so may be justified, for some aquarists, stomatapods make great pets that can live for well over a decade. Of course, this article would be incomplete without a description each side of the dichotomy, so both are detailed here.

If you find yourself with an unwanted mantis, it is probably because you keep finding dead fish or hermit crabs. Worse yet, you might have experienced a broken tank or a wounded finger. Most of the time, they are introduced accidentally as tiny hitchhikers on new live rock. They may survive in a tank undiscovered for some time, if they come in as small juveniles. In the event that you want to remove a mantis shrimp, there are two basic courses of action: you can attempt to trap it, or you can remove the rock within which it makes its home. Commercially made traps are available, but can also be made out of plastic water bottle. The more popular method is to wait until the animal retreats into its rock, then remove it to another tank. When the mantis reemerges, you can steal its rock back and replace it in the main display. A safe alternative is to take out the rock, hold it over a bucket, and pour carbonated water into the shrimps hole. It will eventually emerge and try to escape by falling into the bucket. You can also try eliminate mantis shrimp using Australian dottybacks (Labracinus lineatus), bird wrasses (Gomphosus varius), or octopods. Unfortunately each of these new animals may injure or kill other livestock besides the mantis, and they all should be considered only as a last resort. You will likely find yourself removing them once the stomatapod is removed.

If you would like to keep the stomatapod, it is best to maintain it in a species tank (one made of thick acrylic). Most people keeping mantis shrimp simply found it in their tank one day. However, they can also be purchased if you do not want to wait around for a hitchhiker. The most commonly available ornamental species is Odontodactylus scyllarus, the Peacock Mantis Shrimp. Newly introduced animals may be picky eaters and require live feedings of crab, fish, and hermit crabs, but most will eventually adapt to dried krill, flake food, brine shrimp, and other common aquarium offerings. If well-fed, a mantis may remain docile and leave other livestock alone. Aquarists have had success keeping them in fish-only and reef tanks under these circumstances, but it is impossible to predict when, or if, they will begin to hunt ornamental livestock. The feeding habits of stomatapods dictate that the aquarium systems into which they are placed should have strong filtration. Smashers also need plenty of rockwork, while spearers need to have a deep, open substrate.

Along with the conception that mantis shrimp are aggressive, they are also believed to be shy and reclusive. To the contrary, stomatapods quickly learn to comfortable with their keepers and surroundings. They are known to sit at the openings of their lairs or cruise their tanks, watching everything that happens around them. They even have a tendency to closely watch their keepers, giving the impression that they are inquisitive. They certainly learn quickly whenever food is in question.

For the marine aquarist, a relationship with a mantis shrimp can quickly become a love/hate type of affair. Those that do not want one may find them to be a devilish pest, while their proponents insist that they are a great catch. Without question, stomatapod mantis shrimp are a fascinating and unique oddity that probably have some lessons they have yet to share. In fact, there is one more interesting fact about mantis shrimp: they are the only animal in nature to use a wheel to move. One species, Annosquilla decemspinosa, actually bends its body into a loop when washed shore, and rolls itself back into the sea! Like I said, mantis shrimp are full of surprises.






Works Cited:

Caldwell, R. L. A Test of Individual Recognition in the Stomatopod Gonodactylus festae. Animal Behavior, 33. pp. 101-106. 1985.

Caldwell, R. L. Recognition, Signalling and Reduced Aggression Between Former Mates in a Stomatopod. Animal Behavior, 44. pp. 11-19. 1992.

Chiou et al. Circular Polarization Vision in a Stomatopod Crustacean. Publishing in Current Biology, 18: Mar. 25, 2008. pp. 1-6. 2008.

Fatherree, J. A load of Learnin' About Mantis Shrimp. Reefkeeping Online Magazine, Mar. 2004. URL: < http://reefkeeping.com/issues/2004-03/jf/feature/index.php >

Full, R., K. Earls, M. Wong, and R. Caldwell. Locomotion like a wheel? Nature, 365. p. 495. 1993.

Reaka, M.J. On Learning and Living in Holes by Mantis Shrimp. Animal Behavior, 28. pp. 111-115. 1980.

Roberts, N.W. T.H. Chiou, N.J. Marshall, and T.W. Cronin. A Biological Quarter-Wave Retarder with Excellent Achromaticity in the Visible Wavelength Region. Nature Photonics. 2009.

Weierbach, G. Mantis Shrimp. National Geographic Online. URL: < http://ocean.nationalgeographic.com/wallpaper/ocean/photos/colorful-sea-creatures/colorful04-peacock-mantis-shrimp/ >