From: Ann Mansker 
Subject: Critter of the Week:  Hemisquilla ensigera
Date: 22 Sep 1998 01:13:27 GMT
Newsgroups: ucd.life

The mantis shrimp or stomatopod is neither a mantis nor a shrimp.  A
crustacean in a different order than shrimps, crabs and lobsters, the
"mantis" part of the name refers to a pair of long, powerful appendages
which are used for capturing prey; in their resting state these look
somewhat like the claws of a praying mantis.  Like the insect mantis, the
arms are used to acquire food, but they are employed in one of two ways,
both quite distinct from the grabbing and holding of the insect.

Stomatopod species are either stabbers or smashers.  These images (of a
stabber and a smasher, respectively), show the body shape and weaponry
more clearly than photos of live creatures usually do:

http://tidepool.st.usm.edu/crswr/pix/stomatopod.gif
http://www.scottsbt.com/fishids/phmantis1.gif

Stabbers use the spiky last joint of their raptorial appendages to spear
softbodied prey.  Smashers utilize the enlarged and calcified joint on
each appendage to break the shells of clams and mollusks, in addition to
bludgeoning unarmored targets.  All mantis shrimps are aggressive, as
evidenced by their various common names around the world:  prawn killer,
split toe and thumbsplitter.  The strike is delivered at incredible speed;
the appendage of a spearer accelerates from rest to about 10 meters per
second in as little as 4 milliseconds.

The topic species, Hemisquilla ensigera 
(http://www.blueboard.com/mantis/pics/hemiejh.htm), is a smasher. It is
found off the coast of Southern California to the Gulf of California, and
is one of the largest species at close to a foot long.  Its strike has
nearly the force of a .22 caliber bullet, and captive specimens have been
known to break thick aquarium glass.

Mantis shrimp vision is acute but difficult to imagine.  Their eyes have
up to 16 kinds of photoreceptors, 12 of them cones.  In contrast, humans
get by with only 3 kinds of cones.  They rely on vision for hunting,
and their threat behavior is also highly visual.

Reef aquarists regard mantis shrimp as vicious pests.  They arrive in a
reef tank hidden in crevices in "live rock," which is encrusted with
coraliods and other organisms and thus cannot be sterilized.  Many
stomatopods are capable of taking fish larger than themselves as prey.