''Praya dubia'', the giant siphonophore, lives in the

mesopelagic zone The mesopelagic zone (Greek μέσον, middle), also known as the middle pelagic or twilight zone, is the part of the pelagic zone that lies between the photic epipelagic and the aphotic bathypelagic zones. It is defined by light, and begins ...

bathypelagic zone The bathypelagic zone or bathyal zone (from Greek βαθύς (bathýs), deep) is the part of the open ocean that extends from a depth of below the ocean surface. It lies between the mesopelagic above and the abyssopelagic below. The bathypela ...

at to below

sea level Mean sea level (MSL, often shortened to sea level) is an mean, average surface level of one or more among Earth's coastal Body of water, bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical ...

. It has been found off the coasts around the world, from

Iceland Iceland is a Nordic countries, Nordic island country between the Atlantic Ocean, North Atlantic and Arctic Oceans, on the Mid-Atlantic Ridge between North America and Europe. It is culturally and politically linked with Europe and is the regi ...

in the North Atlantic to

Chile Chile, officially the Republic of Chile, is a country in western South America. It is the southernmost country in the world and the closest to Antarctica, stretching along a narrow strip of land between the Andes, Andes Mountains and the Paci ...

in the South Pacific. ''Praya dubia'' is a member of the order

Siphonophorae Siphonophorae (from Ancient Greek σίφων (siphōn), meaning "tube" and -φόρος (-phóros), meaning "bearing") is an order within Hydrozoa, a class of marine organisms within the phylum Cnidaria. According to the World Register of Marin ...

within the class

Hydrozoa Hydrozoa (hydrozoans; from Ancient Greek ('; "water") and ('; "animals")) is a taxonomy (biology), taxonomic class (biology), class of individually very small, predatory animals, some solitary and some colonial, most of which inhabit saline wat ...

. With a body length of up to , it is the second-longest sea organism after the bootlace worm. Its length also rivals the

blue whale The blue whale (''Balaenoptera musculus'') is a marine mammal and a baleen whale. Reaching a maximum confirmed length of and weighing up to , it is the largest animal known ever to have existed. The blue whale's long and slender body can ...

, the sea's largest mammal, although ''Praya dubia'' is as thin as a broomstick. A siphonophore is not a single, multi-cellular

organism An organism is any life, living thing that functions as an individual. Such a definition raises more problems than it solves, not least because the concept of an individual is also difficult. Many criteria, few of them widely accepted, have be ...

, but a

colony A colony is a territory subject to a form of foreign rule, which rules the territory and its indigenous peoples separated from the foreign rulers, the colonizer, and their ''metropole'' (or "mother country"). This separated rule was often orga ...

of tiny biological components called

zooid A zooid or zoöid is an animal that is part of a colonial animal. This lifestyle has been adopted by animals from separate unrelated taxa. Zooids are multicellular; their structure is similar to that of other solitary animals. The zooids can ...

s, each having evolved with a specific function. Zooids cannot survive on their own, relying on

symbiosis Symbiosis (Ancient Greek : living with, companionship < : together; and ''bíōsis'': living) is any type of a close and long-term biological interaction, between two organisms of different species. The two organisms, termed symbionts, can fo ...

in order for a complete ''Praya dubia'' specimen to survive.

Description

''Praya dubia'' zooids arrange themselves in a long stalk—usually whitish and transparent (though other colours have been seen)—known as a physonect colony. The larger end features a transparent, dome-like float known as a pneumatophore, filled with gas which provides

buoyancy Buoyancy (), or upthrust, is the force exerted by a fluid opposing the weight of a partially or fully immersed object (which may be also be a parcel of fluid). In a column of fluid, pressure increases with depth as a result of the weight of t ...

, allowing the organism to remain at its preferred ocean depth. Next to it are the nectophores, powerful

medusae Jellyfish, also known as sea jellies or simply jellies, are the medusa-phase of certain gelatinous members of the subphylum Medusozoa, which is a major part of the phylum Cnidaria. Jellyfish are mainly free-swimming marine animals, althoug ...

which pulsate in rhythmic coordination which propel ''Praya dubia'' through ocean waters. Together, the array is known as the nectosome. Beneath the nectosome is the siphosome which extends to the far end of ''Praya dubia,'' containing several types of specialized zooids in repeating patterns. Some have a long tentacle used for catching and immobilizing food and distributing their digested nutrients to the rest of the colony. Other zooids known as palpons, or dactylozooids, appear to contain an

excretory system The excretory system is a passive biological system that removes excess, unnecessary materials from the body fluids of an organism, so as to help maintain internal chemical homeostasis and prevent damage to the body. The dual function of excret ...

that may also assist in defense, though little is known about their precise function in ''Praya dubia''. Transparent bracts (also called hydrophyllia), are leaf-shaped organs generally thought to be another type of zooid which covers and forces other zooids to contract in times of danger. Due to their

hydrostatic skeleton A hydrostatic skeleton or hydroskeleton is a type of skeleton supported by hydrostatic fluid pressure or liquid, common among soft-bodied organism, soft-bodied invertebrate animals colloquially referred to as "worms". While more advanced organisms ...

being held together by water pressure above , these animals burst when brought to the surface. The remains of ''Praya dubia'' dredged up in fishing nets resemble a blob of gelatin, which prevented their identification as a unique creature until the 19th century. In 1987,

Monterey Bay Aquarium Research Institute The Monterey Bay Aquarium Research Institute (MBARI) is a private, non-profit oceanographic research center in Moss Landing, California. MBARI was founded in 1987 by David Packard, and is primarily funded by the David and Lucile Packard Foun ...

observed living ''Praya dubia'' during a systematic study of a

water column The (oceanic) water column is a concept used in oceanography to describe the physical (temperature, salinity, light penetration) and chemical ( pH, dissolved oxygen, nutrient salts) characteristics of seawater at different depths for a defined ...

, the animal's natural

habitat In ecology, habitat refers to the array of resources, biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species' habitat can be seen as the physical manifestation of its ...

, in

Monterey Bay Monterey Bay is a bay of the Pacific Ocean located on the coast of the U.S. state of California, south of the San Francisco Bay Area. San Francisco itself is further north along the coast, by about 75 miles (120 km), accessible via California S ...

Behavior

''Praya dubia'' is an active swimmer that attracts its prey with bright blue bioluminescent light. When it finds itself in a region abundant with food, it holds its position and deploys a curtain of tentacles covered with

nematocysts A cnidocyte (also known as a cnidoblast) is a type of cell containing a large secretory organelle called a ''cnidocyst'', that can deliver a sting to other organisms as a way to capture prey and defend against predators. A cnidocyte explosively ...

which produce a powerful, toxic sting that can paralyze or kill prey that happen to bump into it. ''Praya dubia'''s diet includes gelatinous sea life, small

crustaceans Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of Arthropod, arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquat ...

, and possibly small fish and fish larvae. It has no known predators. A ''Praya dubia'' specimen, filmed in its native habitat, was featured in Episode 2 of the

David Attenborough Sir David Frederick Attenborough (; born 8 May 1926) is an English broadcaster, biologist, natural historian and writer. He is best known for writing and presenting, in conjunction with the BBC Studios Natural History Unit, the nine nature d ...

television series ''

Blue Planet II ''Blue Planet II'' is a 2017 British nature documentary series on marine life produced as a co-production between the BBC Natural History Unit, BBC America, Tencent, WDR, France Télévisions and CCTV-9 in partnership with The Open Universit ...

'', produced for the

BBC The British Broadcasting Corporation (BBC) is a British public service broadcaster headquartered at Broadcasting House in London, England. Originally established in 1922 as the British Broadcasting Company, it evolved into its current sta ...

References

External links

Giant Siphonophore Sighting
YouTube, 22 May 2015, by E/V Nautilus during the 2015 ECOGIG dives in the Gulf of Mexico, Accessed 28, January 2018..
Deep sea siphonophore off Roatán Honduras - 2300 feet
YouTube, 10 June 2013, Roatán Institute of Deepsea Exploration, Accessed 28, January 2018.
Praya dubia Distribution Map at Ocean Biogeographic Information System

Praya dubia Habitat at Encyclopedia of Life
{{Taxonbar, from=Q2512355 Prayidae Cnidarians of the Atlantic Ocean Cnidarians of the Caribbean Sea Bioluminescent cnidarians Biota of the Gulf of Mexico Marine fauna of Europe Marine fauna of North America Animals described in 1827