Firefly squid

Firefly squid

Firefly squid, Sparkling enope squid, Hotaru-ika

2 languages
Kingdom
Phylum
Class
Order
Genus
SPECIES
Watasenia scintillans
Length
7.62 cm

The firefly squid (Watasenia scintillans ), also commonly known as the sparkling enope squid or hotaru-ika in Japan, is a species of squid in the family Enoploteuthidae. It is the sole species in the monotypic genus Watasenia. These tiny squid are found on the shores of Japan in springtime during spawning season, but spend most of their lives in deeper waters between 200 and 400 metres (700 and 1,300 feet; 100 and 200 fathoms). They are bioluminescent organisms and emit blue light from photophores, which some scientists have hypothesized could be used for communication, camouflage, or attracting food, but it is still unclear in the scientific community exactly how this species uses their bioluminescence. The firefly squid is a predator and actively hunts its food, which includes copepods, small fish, and other squids. The lifespan of a firefly squid is about one year. At the end of their lives females return close to shore to release their eggs, and then die shortly thereafter. This mass migration of firefly squid to the shore is a lucrative business for Japanese fishermen, and during spawning season many go out to the bays to collect the dying squid. Many more also visit Japan during spawning season to see the bright blue light created from the firefly squid's bioluminescence light up the bay, making their spawning season not only a fishing opportunity but also a tourist attraction.

Appearance

The firefly squid belongs to the Cephalopoda class and the superorder Decapodiformes, commonly known as squid. Their body is divided between a distinct head and a mantle, and the layout of the body is bilaterally symmetrical. They are soft-bodied organisms which contain a skeletal structure composed of chitin. They have relatively large eyes, eight arms, and two tentacles. They are further classified into the order Oegopsida for possessing the characteristic traits of having no tentacle pockets in the head and no suckers on the buccal supports. They belong to the family of Enoploteuthidae, based on the hooks on their tentacles.

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On average an adult firefly squid is approximately 7.5 cm (3 in) in length. They are brown/red in color, but emit blue and green light by their photophores. Firefly squid have three types of photophores on its body. There are multiple (800-1000) small photophores over the ventral surface of its body, five larger photophores around the lower margins of each eye, and three very large photophores at the tip of each of the fourth pair of ventral legs. The photophores that dot the body of the squid produce two different wavelengths of light, both blue and green bioluminescence, while those around the eye and on the legs only produce blue wavelength light. The reactant luciferin and the necessary enzyme luciferase are located in a crystalline structure within rod like bodies in their photophores. Firefly squid are the only cephalopods to have this structural arrangement which increases the efficiency of its bioluminescence and allows the light to be directed downward in a cone-like projection. This directed cone of bioluminescence is hypothesized to allow the Firefly squid to better detect its prey and predators from below and attract small fish to eat. The photophores on the tips of its fourth ventral legs produce a very intense light that can be seen by the naked eye.

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Distribution

Geography

Continents
Biogeographical realms

The firefly squid inhabits the waters off the coast of Japan. The depth at which these squids can be found varies (300–400 m or 1,000–1,300 ft during the day, and 20–60 m or 70–200 ft during the night) over the course of a day, as they are one of the several species of squid that participates in diel vertical migration. For this reason, they also experience a significant change in environmental temperatures throughout the course of a day(3–6 °C or 37–43 °F during the day and 5–15 °C or 41–59 °F during the night). The firefly squid is especially well known for its yearly migration to the coastal waters of Toyama Bay for the purpose of reproduction.

Climate zones

Diet and Nutrition

The diet of a firefly squid changes throughout its life stages. During its paralarval stage, its diet is primarily composed of calanoid copepods (zooplankton). Subadult and adult stages see an increase in dietary diversity to include planktonic crustaceans, fishes, and squid.

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Firefly squid face high predation rates and may serve as the primary food source for some predatory species including northern fur seals, particularly during their yearly migration. The squid spends the day at depths of several hundred meters, returning to the surface when night falls. It uses its abilities to sense and to produce light for counter-illumination camouflage: it matches the brightness and colour of its underside to the light coming from the surface, making it difficult for predators to detect it from below. As a participant in diel vertical migration, firefly squid primarily feed during the night. This feeding strategy is reflected in the squid’s gut anatomy, which has a longer cecum that allows it to absorb nutrients during the day when its metabolic rate is lower.

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Mating Habits

References

1. Firefly squid Wikipedia article - https://en.wikipedia.org/wiki/Firefly_squid
2. Firefly squid on The IUCN Red List site - https://www.iucnredlist.org/species/163146/977074

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