In the tropical oceans of the South Pacific lurks a predator that violently launches itself at its prey and spears it with raptor-like blades. These animals have been known to reach speeds so great that they can break aquarium glass. They are a crustacean commonly known as mantis, shrimp and they belong to the phylum Arthropoda and the class Stomatopoda. All have an exoskeleton, which means their bodies do not have internal bones for support. Other characteristics of Arthropod's are segmented bodies and bilateral symmetry. The exoskeleton is made of chitin, lipids, carbohydrates and protein. As arthropods, including mantis shrimp, grow they produce a newer, softer exoskeleton underneath the old exoskeleton and it must be shed or molted. The exoskeleton forms jointed appendages, such as antennae and legs, that allow for movement and flexibility. Mantis shrimp are renowned for their unusual method of being able to break the shells of their bivalve mollusk prey with brief, powerful strikes of their raptorial appendages(Patek and Caldwell, 2005).
Mantis shrimp are in the subphylum Crustacea, and the Class Malacostraca. Malacostracans have three-party body; head, thorax and abdomen and compound stalked or sessile eyes. Other characteristics of the Malacostracans are a two-chambered stomach and centralized nervous system. The eyes of mantis shrimp are unique and are composed of three parts; a dorsal and ventral hemisphere separated by a central mid-band with three pseudo-pupils (Land, et al, 1990). Mantis shrimps are aggressive predators whose behavior is largely guided by vision (Caldwell and Dingle, 1976).
The Stomatopods are predators that hunt and kill animals. They attack and capture fish, mollusks and other crustaceans with specialized forelimbs, the raptorial appendages. High speed imaging revealed that mantis shrimp forelimbs reach maximum speeds from 12-23 m/s (Patek and Caldwell, 2005). Also, cavitation bubbles (vapor cavities in a liquid), formed between the appendage and a snail shell when these were the prey (Patek and Caldwell, 2005). These strikes causes the snail shell to crack open, making it easier for the Stomatopoda to kill and eat this prey.
Close evolutionary relatives to the Stomatopods are in the order Decapoda, which uses a similar arm mechanism. Because all Stomatopods have the raptorial appendage and exhibit an aggressive behavior, it is probable that both the Decapoda and Stomatopoda, evolved this appendage along the evolutionary tree. Decapods do not show the same aggressive behavior. One Stomatopoda species, Daidal acanthocercus, lived during the Carboniferous period(Fig. 1). Although extinct, it had a similar body structure and the pre-raptorial appendages which are used for protection of their territories.
Because of their aggressiveness and the face that they have dangerous weapons, Stomatopods have developed a very ritualized fighting system for territories, consisting of threat displays. Nevertheless, these...