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| ===Bioluminescence=== | | ===Bioluminescence=== |
| Krill are often referred to as ''light-shrimp'' because they can emit light, produced by [[bioluminescence|bioluminescent]] organs. These organs are located on various parts of the individual krill's body: one pair of organs at the [[eyestalk]] (cf. the image of the head above), another pair on the hips of the second and seventh [[thoracopod]]s, and singular organs on the four [[pleonsternite]]s. These light organs emit a yellow-green light periodically, for up to 2–3 s. They are considered so highly developed that they can be compared with a torchlight: a concave reflector in the back of the organ and a lens in the front guide the light produced, and the whole organ can be rotated by muscles. The function of these lights is not yet fully understood; some hypotheses have suggested they serve to compensate the krill's shadow so that they are not visible to predators from below; other speculations maintain that they play a significant role in [[mating]] or [[Shoaling and schooling|schooling]] at night. | | Krill are often referred to as ''light-shrimp'' because they can emit light, produced by bioluminescent organs. These organs are located on various parts of the individual krill's body: one pair of organs at the eyestalk, another pair on the hips of the second and seventh thoracopods, and singular organs on the four pleonsternites. These light organs emit a yellow-green light periodically, for up to 2–3 seconds. They are considered so highly developed that they can be compared with a torchlight: a concave reflector in the back of the organ and a lens in the front guide the light produced, and the whole organ can be rotated by muscles. The function of these lights is not yet fully understood; some hypotheses have suggested they serve to compensate the krill's shadow so that they are not visible to predators from below; other speculations maintain that they play a significant role in mating or schooling at night. |
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| The krill's bioluminescent organs contain several fluorescent substances. The major component has a maximum [[fluorescence]] at an excitation of 355 [[Nanometre|nm]] and emission of 510 nm.<ref name="HS01">{{cite conference |author1=H. Rodger Harvey |author2=Se-Jong Ju |url=http://www.ccpo.odu.edu/Research/globec/3sciinvest/harvey.htm |title=Biochemical determination of age structure and diet history of the Antarctic krill, ''Euphausia superba,'' during austral winter |conference=Third U.S. Southern Ocean GLOBEC Science Investigator Meeting |location=Arlington |date=10–12 December 2001}}</ref> | | The krill's bioluminescent organs contain several fluorescent substances. The major component has a maximum fluorescence at an excitation of 355 nanometers. |
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| [[File:Caridoid escape reaction.gif|thumb|Lobstering krill]]
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| ===Escape reaction=== | | ===Escape reaction=== |
| Krill use an [[escape reaction]] to evade [[predator]]s, swimming backwards very quickly by flipping their rear ends. This swimming pattern is also known as [[Caridoid escape reaction|lobstering]]. Krill can reach speeds of over {{convert|0.6|m/s}}.<ref name="Kils82">{{cite book|author=Uwe Kils |url=http://www.ecoscope.com/biomass3.htm |title=Swimming behaviour, swimming performance and energy balance of Antarctic krill ''Euphausia superba'' |series=BIOMASS Scientific Series |volume=3 |pages=1–122 |year=1982 |isbn= |publisher=}}</ref> The [[Induction period|trigger]] time to optical [[stimulus (physiology)|stimulus]] is, despite the low temperatures, only 55 [[millisecond|ms]]. | | Krill use an escape reaction to evade predators, swimming backwards very quickly by flipping their rear ends. This swimming pattern is also known as "lobstering". Krill can reach speeds of over 0.6 meters per second. |
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| ==Geographic distribution== | | ==Geographic distribution== |