Mantis shrimp: Difference between revisions

| title = Mantis shrimp

| clade = Stomatopoda

| known for = Punching; vision; aquarium damage

| strike speed = up to 23 m/s

| photoreceptor types = 12 to 16

| colour discrimination = worse than yours

}}

'''Mantis shrimp''' are marine crustaceans of the order '''Stomatopoda''', comprising about 450 species. They are neither mantises nor shrimp, which is the least surprising thing about them.

== The strike ==

The "smasher" species strike with a calcified club that accelerates at up to 10,000 g, reaching about 23 m/s from a standing start.<ref name="patek">S. N. Patek, W. L. Korff and R. L. Caldwell, "Deadly strike mechanism of a mantis shrimp", ''Nature'' 428 (2004), pp. 819-820.</ref> The limb moves so quickly that the water in front of it cannot get out of the way, so it boils: the strike produces [[cavitation]] bubbles whose collapse generates a second shock wave, a flash of light, and briefly, temperatures that have been estimated in the thousands of kelvin.<ref name="patek" />

The animal therefore hits its prey twice, the second time with an implosion, and it does this at a body length of about 10 cm. The peacock mantis shrimp (''Odontodactylus scyllarus'') is known to aquarists as the "thumb splitter" and is regularly removed from display tanks for breaking the glass.<ref>Roy L. Caldwell and Hugh Dingle, "Stomatopods", ''Scientific American'' 234:1 (1976), pp. 80-89.</ref>

== Vision ==

Mantis shrimp have between 12 and 16 classes of photoreceptor, against three in humans, and several species can detect circularly polarised light, which no other animal is known to do.<ref>Tsyr-Huei Chiou et al., "Circular polarization vision in a stomatopod crustacean", ''Current Biology'' 18:6 (2008), pp. 429-434.</ref>

This is widely reported to mean that they see a richer world of colour than we do. In 2014 the claim was tested directly: trained animals were asked to discriminate between wavelengths, and they failed at differences smaller than about 25 nm, which is roughly ten times worse than a human.<ref name="thoen">Hanne H. Thoen et al., "A different form of color vision in mantis shrimp", ''Science'' 343:6169 (2014), pp. 411-413.</ref> The current interpretation is that the animal does not compare its receptors against each other at all. It scans, registers which channel fires, and acts, trading accuracy for speed.<ref name="thoen" />

The creature with the most colour receptors ever documented uses them to make a snap judgement.

== Conservation and captivity ==

Smashers are kept singly, in acrylic rather than glass, by aquarists who have learned this the second way. Several species are fished commercially; in Japan ''Oratosquilla oratoria'' is eaten as ''shako''.

== See also ==

* [[Tardigrade]]

* [[Cavitation]]

[[Category:Animals]]

[[Category:True but improbable]]