If the
shrimp we ate were anything like mantis shrimp, there would be a whole lot of nine-fingered fishers out there; pound for pound, there is no more dangerous predator in or out of the ocean. The
diving community has given them the apt nickname of "thumb splitters", and of the few people even aware of their existence, all most care to know is that these things can break your hand in a heartbeat. Biologists refer to them by the technical term
stomatopods, and aside from a few adventurous
aquarists, they are the only ones to appreciate the uniqueness and fascination of these
crustaceans.
They belong to the diverse class
Malacostraca, which encompasses
shrimp as well as
crabs and
isopods (
pillbugs); they belong to their own subclass
Hoplocaridia (“armed shrimp”) and order
Stomatopoda. They are further classified as either “spearers” or “smashers”, depending on the means by which they destroy their foes.
Mantis shrimp designated as
spearers wield sharp blades at the ends of their arms, which can neatly hole much larger
fish,
octopi, or other soft-bodied animals. A dangerously barbed "finger" is folded up within a groove of this blade, able to snap out with the speed and force of a small-caliber bullet. Unfolding in eight milliseconds and travelling ten metres a second, it is among the fastest motions that any animal is capable of.
More aggressive still are the
smashers, with massive,
calcified elbow-clubs that they bring to bear against prey such as
crabs,
lobsters and
clams. They frequently obliterate
crustaceans much larger than themselves, reducing huge
crabs to delicious fragments.
Clams and
snails are picked up, leaned carefully against rocks, and broken open. This variety of mantis shrimp has a deserved reputation for being able to
shatter aquarium glass, although only the larger specimens have this level of strength.
Depending on their species, mantis shrimp grow from two to thirty centimetres in length. Their coloration ranges from drab gray or dun to a prismatic, riotous beauty. Although superficially resembling
crayfish in their body structure -- an elongated
carapace, eyes on stalks, and eight main legs followed by
swimmerets and a flexible lobsterlike tail or
telson -- their unique predatory arms make them immediately distinguishable.
One of the most fascinating aspects of
stomatopod anatomy is their highly developed vision system, far surpassing that of
humans and almost all other forms of life. Each crazily spinning, stalked
compound eye has three separate regions: upper and lower hemispheres that serve mainly to pick out forms, separated by a color-sensing midband. As a consequence, each eye can see an object from three different perspectives, and has
depth perception and
trinocular vision on its own. (We need both
eyes for
depth perception and mere
binocular vision.)
The middle band of the mantis shrimp's
eye is equipped with ten different varieties of
visual pigment, as opposed to our
eye's three (red, green and blue). Eight of the mantis shrimp's
pigments are dedicated to color vision alone; their visible spectrum, encompassing eight
primary colors, is the key to a visual world unimaginable to
humans. They can identify roughly ten thousand distinct colors, compared to the human maximum of one thousand. The additional pigments are dedicated to viewing the
polarization and distribution of light, qualities
human eyes can only faintly perceive, but which are essential in the low-
contrast underwater landscape.
Their
intelligence is likewise highly developed; researchers have shown it to be roughly equal to that of that notorious unbackboned
intellectual, the
octopus. Mantis shrimp can be trained to differentiate exceedingly similar colors and geometric shapes, and solve simple puzzles such as unwrapping a rubber band from a food item.
Mantis shrimp are the only
invertebrates which can be consistently shown to discriminate between individual members of their species; this is probably a result of fierce competition for a limited amount of
suitable living spaces, leading them to view competitors as unique individuals, and treat them intelligently. Certain species are even monogamous.
Stomatopods have a fairly wide distribution throughout the shallow and warm waters of the world, found ten to twenty metres down in areas as diverse as
Indonesia,
Florida, and the
Isle of Wight. Some species burrow exclusively, tunneling through sand and mud, whereas others prefer pre-formed caverns in
coral reefs and rocks. They spend the majority of time tucked neatly inside their lairs, waiting for unsuspecting creatures to come close; extremely wary of their relatively undefended backsides, they seek shelter whenever possible. Some species are known to block their lair entrances with rubble at night.
Like all
crustaceans, they are egg-layers; the female can store
fertilized eggs for three months or more after copulation. Eggs are exuded in a
globby mass that she carries around with her until they hatch; typically the
larvae leave immediately, although in a few species, they stay with their mother for a week or ten days before seeking their fortune, progressing through several larval and juvenile growth stages. Larvae are ferocious and
cannibalistic, which explains the limited success of rearing them in home
aquaria. Even in their earliest growth stages, their fearsome forelimbs are present, and frequently used to dismember other
larvae.
The average lifespan of a captive mantis shrimp is three to four years, and researchers estimate that they may live much longer in their natural habitat, with certain species able to exceed twenty years.
The fascination of these creatures makes their relative obscurity all the stranger. They could teach us a thing or two; not just about eating
clams and being pretty, but about percieving wonderful
psychedelic landscapes, and kicking lots and lots of ass. And in the end, isn’t that what it’s all about?
Sources:
http://www.blueboard.com/mantis/
http://ozreef.org/reference/mantis_shrimp.html
http://www.x-entertainment.com/articles/0723/