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What are stomatopods?

"The follower was aglow with life, gold marked in detail with red and green and brown, like banners carried forward above an advancing column. Long antennae waved as if for balance above bulbous, short-stalked eyes. And underneath the eyes a coil of heavy forelimbs rested..."
- from "Smasher" by Fred Saberhagen


Odontodactylus scyllarus.
O. scyllarus by Jeffrey Rosenfeld

Stomatopods are predatory crustaceans that live in the shallow waters of tropical and subtropical seas. They are not closely related to shrimps or the other decapod crustaceans, although they are commonly known as "mantis shrimps" due to the raptorial appendages that they use to efficiently capture and subdue prey. These animals range in size from 1-2 cm to more than 30 cm in some Lysiosquilla sp., and are one of the most aggressive and pugnacious of all creatures.

The larger stomatopods, in particular, are capable of tackling much larger animals in defence of themselves or during prey capture. According to Dr. Roy Caldwell, who has studied mantis shrimps for most of his professional life, a wholesaler once offered him two Odontodactylus scyllarus specimens, which had killed 6 clown trigger fishes (which are notorious for preying on crustaceans) in a single night. He has also seen a fully grown 15 cm peacock mantis kill a larger 20 cm Clown Trigger. Finally, a Hemisquilla ensigera smasher beat the heck out of a much larger octopus that had strayed too close to its burrow, using its raptorial appendages to repeatedly smash at the cephalopod's soft exterior.

 
General Structure (11 kb)
- Courtesy J. Taylor,Museum of Victoria, Australia.
 

The group can be divided functionally into two groups: the spearers, who use forelimbs with numerous spines to capture mainly soft-bodied prey like fishes and shrimps, and the smashers, who possess clublike appendages to crush hard-shelled animals such as crabs, clams, and snails. The spearers are in general larger in size and less aggressive than the smashers, and they tend to construct their burrows in soft substrates like mud and sand. The strike of one of these is considered to be one of the fastest movements known in the animal kingdom, with velocities on the order of 10 meters per second, and even rapidly swimming fish are easily seized, pierced, and immobilized by the spined appendages.

 
Raptorial Appendages (54 kb)
Spear (l) and club (r) appendages, courtesy of Dr. Roy Caldwell
 

The smashers live mainly in hard substrates such as corals and rocks, and employ their heavily calcified "club" to reduce prey animals to scattered bits of matter. The efficiency of their weapons is such that these mantis shrimps frequently tackle and subdue armored crabs larger than themselves, using the appendages to break the animals' claws, legs, and carapace, before dragging the battered remains to their burrows for leisurely consumption. Less mobile prey such as clams and snails are simply taken home, wedged against a wall, then cracked open. The strike of one of the larger smashers (25 cm long Hemisquilla ensigera) has been estimated to produce a force approaching that of a 22 caliber bullet, and these animals have been reported to break open aquarium walls made of double layered safety glass. It is no wonder then that mantis shrimps are also known as "thumb splitters."

The mantis shrimps are also world-renowned as having the world's most sophisticated vision. According to Dr Justin Marshall, the stomatopod eye "contains 16 different types of photoreceptors (12 for colour analysis, compared to our 3 cones), colour filters and many polarisation receptors, making it by far the world's most complex retina." Mantis shrimps can thus see polarized light and 4 colors of UV (ultraviolet) light, and they may also be able to distinguish up to 100,000 colors (compared to the 10,000 seen by human beings). Eat your heart out, Superman!

- A. San Juan (last revised: Nov 10,2002)

     
This animation was constructed from diagrams in the paper "Stomatopods" by Caldwell and Dingle in Scient Am 234, 80-89.  
     

References:

Web Site Author: A. San Juan
Site Created February 3, 1998
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