''Vargula hilgendorfii'', sometimes called the sea-firefly and one of three bioluminescent species known in Japan as umi-hotaru (海蛍), is a species of

ostracod Ostracods, or ostracodes, are a class of the Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 70,000 species (only 13,000 of which are extant) have been identified, grouped into several orders. They are small crustaceans, typi ...

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group can ...

. It is the only member of genus '' Vargula'' to inhabit Japanese waters; all other members of its genus inhabit the

Gulf of Mexico The Gulf of Mexico ( es, Golfo de México) is an ocean basin and a marginal sea of the Atlantic Ocean, largely surrounded by the North American continent. It is bounded on the northeast, north and northwest by the Gulf Coast of the United ...

, the

Caribbean Sea The Caribbean Sea ( es, Mar Caribe; french: Mer des Caraïbes; ht, Lanmè Karayib; jam, Kiaribiyan Sii; nl, Caraïbische Zee; pap, Laman Karibe) is a sea of the Atlantic Ocean in the tropics of the Western Hemisphere. It is bounded by Mexico ...

, and waters off the coast of

California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the m ...

. ''V. hilgendorfii'' was formerly more common, but its numbers have fallen significantly.

Description

''V. hilgendorfii'' is a small animal, only 3 millimetres long. It is nocturnal and lives in the sand at the bottom of shallow water. At night, it feeds actively.

Bioluminescence

''V. hilgendorfii'' is known for its bioluminescence. It produces a blue-coloured light by a specialized chemical reaction of the substrate

luciferin Luciferin (from the Latin ''lucifer'', "light-bearer") is a generic term for the light-emitting compound found in organisms that generate bioluminescence. Luciferins typically undergo an enzyme-catalyzed reaction with molecular oxygen. The resul ...

and the enzyme luciferase. The luciferase enzyme consists of a 555-

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha a ...

-long peptide with a molecular mass of 61627 u, while the luciferine vargulin has only a mass of 405.5 u. A suggested biosynthesis for vargulin divides the molecule into a

tryptophan Tryptophan (symbol Trp or W) is an α-amino acid that is used in the biosynthesis of proteins. Tryptophan contains an α-amino group, an α-carboxylic acid group, and a side chain indole, making it a polar molecule with a non-polar aromatic ...

, an arginine and an isoleucine subunit. The maximum in the

wavelength In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, t ...

of the luminescence is dependent on pH and salinity of the water in which the reaction takes place. It varies between 448 and 463 nm, with the maximum being at 452 nm in sea water. The substrate oxidizes when ejected from the upper-lip gland, with luciferase as a catalyst. The reaction produces

carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...

oxyluciferin Luciferin (from the Latin ''lucifer'', "light-bearer") is a generic term for the light-emitting compound found in organisms that generate bioluminescence. Luciferins typically undergo an enzyme-catalyzed reaction with molecular oxygen. The resu ...

, and blue light. As an intermediate, a 1,2-dioxetane ring is formed; this intermediate is also formed in reaction of other bioluminescent lifeforms and also in the chemoluminescence of

glow stick A glow stick, also known as a light stick, chem light, light wand, light rod, and rave light, is a self-contained, short-term light-source. It consists of a translucent plastic tube containing isolated substances that, when combined, make light ...

Distribution

''V. hilgendorfii'' is indigenous to the water off the southern Japanese coast. DNA and RNA analysis indicated that ''V. hilgendorfii'' migrated slowly northward after the last ice age. The poor swimming abilities and the fact the eggs are hatched in the uterus and live young are born limit the ability to migrate.

History

The species was first described by

Gustav Wilhelm Müller Christian Gustav Wilhelm Müller (17 February 1857, Mühlberg near Erfurt – 18 February 1940) was a German zoologist specializing in Ostracoda. In 1895 he succeeded Carl Eduard Adolph Gerstaecker as director of the zoological museum at Grei ...

in 1890. He named the species after the

zoologist Zoology ()The pronunciation of zoology as is usually regarded as nonstandard, though it is not uncommon. is the branch of biology that studies the animal kingdom, including the structure, embryology, evolution, classification, habits, and d ...

Franz Martin Hilgendorf Franz Martin Hilgendorf (5 December 1839 – 5 July 1904) was a German zoologist and paleontologist. Hilgendorf's research on fossil snails from the Steinheim crater in the early 1860s became a palaeontological evidence for the theory of ev ...

(1839–1904). The bioluminescence of ''V. hilgendorfii'' was a research topic for a long time; the first research dates back to the year 1917. During

World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposing ...

, the Japanese army sometimes used dried sea-firefly as a light source to discreetly read maps in their dim light. In 1962, the name of the species was changed from ''Cypridina hilgendorfii'' to ''Vargula hilgendorfii''. In 1968, Japanese scientists were able to determine the structure of the luciferin vargulin.

References

{{Authority control Myodocopida Bioluminescent ostracods Crustaceans described in 1890