The word "sea-firefly (in Japanese "umi-hotaru")" means chemiluminous myodocopids.
A species named "Vargula hilgendorfii" is one of the most famous luminous species.
This picture shows left side of Vargula hilgendorfii.
female (left) and male (right)
WHAT ARE THEY?
They are classifiied into....
class: Crustacea
sub-class: Ostracoda
order: Myodocopida
sub-order: Myodocopina
family: Cypridinidae
genus: Vargula
species name: hilgendorfii
V. hilgendorfii is usual myodocopid species in the sea around Japan.
BODY STRUCTURE
Maybe you think that sea-fireflies are likely to egg. Their carapace defined outline of them. Inside the carapace, there is body of them called "soft-body". They have 7 pairs of appendages. Each appendage is specializing functionally and morphologically.
WHERE DO THEY LIVE?
They live in the sea around Japan. They are nekto-benthos and nocturnal animal. In day time, they are hiding into sand.
WHAT DO THEY EAT?
Mainly meats. They are not only a scavenger, but also a predator. They attack and eat sandworm etc.
like Piranhas!
BODY SIZE
approximately 2.9-3.5mm．A female is larger than a male.
Their lifeCycle
5 times of moulting make them adult. It takes 4-5 months to grow up. And adult individuals can live 6 month or longer, so sea-fireflies may live about a year or longer.
Adult female individual copulate with male, and lays 30-60 eggs in her egg-pouch. At copulation, male shows courtship display. We can see "coultship dance" as spiral rotation of blue light. Embryos are preserved at egg-pouch until growing up to juvenile and starting swimming. Mother individual releases eggs at a full-moon night.
:Mother: Egg pouch exists on rear of carapace.
:Embryonic development
Large specimen (positioned lower right) is a swimming juvenile. The orange line shows hatching, and the green line shows starting swimming.
Sea-firefries are a kind of Crustacea, but there is no nauplius larval stage. A-5 juveniles has almost completely and functional appendages except for 7th limbs. 7th limb on A-5 juveniles are immature.
HOW THEY EMIT LIGHT?
Sea-fireflies emit lignt by chemical reaction. They eject enzyme and substrate from their upper lip.
Substrates (Vargula luciferin) are oxidized by enzymes (Vargula luciferase) and become oxyluciferin. And redundant energy become light (peak wavelength 460nm).
Unlike firefly, luminous reaction needs only substrate, enzyme and oxygen. There is no needs for ATP or other matters.
SEA-FIREFLIES DIFFER TO NOCTILCAS
Noctilca -maybe most famous luminous creature in the sea- is a kind of phytoplankton. (In detail, a classification of dinoflagellate does not clarify....phytoplankton or zooplankton?)
Unlike sea-firefly, luminescence of noctilca is considered to be the accidental by-product of energy metabolism
WHY THEY EMIT LIGHT?
Researchers think that luminescence of sea-fireflies is used for...
1.courtship ritual (by male)
2.surprising predators (called "light bomb")
3.response to a rapid change of environment, such as salinity and or temperature
But, truth is unknown, because of all the sea-fireflies (contain male, female and jevenile).