Summary

Yolana Kailichova (2012)

                                                                   THE MANTIS SHRIMP

The mantis shrimp, order Stomatopoda is neither a shrimp nor a mantid, rather its common name is due to its superficial resemblance to both animals. This likeness is reflected in both its raptorial appendage, a similar mechanism as in the praying mantis, and its general body plan, which does not differ markedly from its sister order, Decapoda.

The mantis shrimp’s ancestor can be dated back to fossils from the Devonian period circa 400 million years ago. (Figure above: Yohoia tenuis, a species of Squilla stomatopod discovered fossilized in the Burgess Shale deposits in Canada by Walcott, 1912. Fossil specimens were photographed under polarised lighting conditions.)

Over this evolutionary time period, its set of powerful raptorial claws have taken the form of either spearing or smashing appendages (Caldwell & Dingle, 1976).  'Smashers’ crack open the hard shells of prey such as hermit crabs. The appendages of ‘spearers’ meanwhile spear and collect soft-bodied animals such as fish. At least two other aspects of its ecological niche are implicated in the evolution of the animal.  These include cavity dwelling for protection during its molt and which frequently results in conspecific fighting for resources.  The second aspect is its wide distribution, residing globally from depths of 10m to 60m. Its effective weapon system is thus used for predation, defence and construction of its cavity.

Biomechanic studies of the stomatopod’s strike have identified one of the fastest reflexes of any animal (Patek et al., 2005). The strike may clock speeds of 20ms^-1 and this notably, is against theresistance of water (Patek & Caldwell, 2004; Patek et al., 2007).  The impact of such blows has been measured to reach peak forces of 1,500 N (55kgs^-1).  Extraordinary, for an organism which measures only centimetres in length. Theoretically, to best utilise such an effective weapon system, several taxa have evolved superior vision systems, possessing up to 16 photoreceptors, which may facilitate the visualisation of colours, UV-,  linear- and circular-polarising light (Marshall et al., 2007).

Several studies have also examined the behaviour of the animal and its aggressive response over various resources and over differing stages of its life history (Dingle,1969; Reaka, 1972; Parker, 1974; Caldwell, 1979; Wortham-Neal, 2001). Some mantis shrimp have been observed delivering repeated blows up to larger shelled prey hundreds of times, up to 3 hours in duration (Patek et al., 2004).

A short study was conducted on Heron Island to examine the impact from the raptorial strike of one species of mantis shrimp. The impacts of left and right appendages were compared over multiple successive blows within a time period. Gonodactylaceus falcatus, a species of smashing stomatopod, was the subject of this impact study.