Praya dubia
{{Short description|Species of hydrozoan}}
{{Speciesbox
| image = Praya dubia.png
| image_caption = Illustration of a giant siphonophore
| taxon = Praya dubia
| authority = (Quoy & Gaimard, 1827)
| synonyms =
- Diphyes dubia Quoy & Gaimard, 1833
- Nectocarmen antonioi Alvariño, 1983
- Praia dubia Blainville, 1830
- Prayoides intermedia Leloup, 1934
}}
Praya dubia, the giant siphonophore, lives in the mesopelagic zone to bathypelagic zone at {{convert|700|m||abbr=on}} to {{convert|1000|m||abbr=on}} below sea level. It has been found off the coasts around the world, from Iceland in the North Atlantic to Chile in the South Pacific.{{cite web |url=http://iobis.org/explore/#/taxon/497295 |website=iobis.org |access-date=2018-01-30|title=Ocean Biodiversity Information System }}
Praya dubia is a member of the order Siphonophorae within the class Hydrozoa. With a body length of up to {{convert|50|m||abbr=on}}, it is the second-longest sea organism after the bootlace worm. Its length also rivals the blue whale, the sea's largest mammal, although Praya dubia is as thin as a broomstick.{{cite news |url=http://www.jpost.com/Health-and-Sci-Tech/Science-And-Environment/Beauty-and-the-deep |title=Beauty and the deep |work=The Jerusalem Post {{!}} JPost.com |access-date=2018-01-30}}{{cite web |url=https://www.montereybayaquarium.org/animal-guide/invertebrates/giant-siphonophore |title=Giant siphonophore, Deep Sea, Invertebrates, Praya sp at the Monterey Bay Aquarium |website=montereybayaquarium.org |language=en |access-date=2018-01-30}}
A siphonophore is not a single, multi-cellular organism, but a colony of tiny biological components called zooids, each having evolved with a specific function. Zooids cannot survive on their own,The Deep; the University of Chicago Press, London (2007) relying on symbiosis 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{{cite web |url=https://www.nytimes.com/2017/12/19/science/deep-sea-food-web.htm |title=What Eats What: A Landlubber's Guide to Deep Sea Dining |website=The New York Times |access-date=2017-12-19}})—known as a physonect colony.{{cite web |url=https://www.biology-online.org/dictionary/Siphosome |title=Siphosome - Biology-Online Dictionary |website=biology-online.org |language=en |access-date=2018-01-30}} The larger end features a transparent, dome-like float known as a pneumatophore,{{cite web |url=https://www.biology-online.org/dictionary/Pneumatophore |title=Pneumatophore - Biology-Online Dictionary |website=biology-online.org |language=en |access-date=2018-01-30}} filled with gas which provides buoyancy, allowing the organism to remain at its preferred ocean depth. Next to it are the nectophores,{{cite web |url=https://www.biology-online.org/dictionary/Nectophore |title=Nectophore - Biology-Online Dictionary |website=biology-online.org |language=en |access-date=2018-01-30}} powerful medusae which pulsate in rhythmic coordination which propel Praya dubia through ocean waters.{{cite web |url=https://www.biology-online.org/dictionary/Medusa |title=Medusa - Biology-Online Dictionary|website=biology-online.org |language=en |access-date=2018-01-30}} 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 that may also assist in defense, though little is known about their precise function in Praya dubia.{{cite journal |title=Dactylozooids |url=https://encyclopedia2.thefreedictionary.com/Dactylozooids |journal=The Free Dictionary}} 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 being held together by water pressure above {{convert|460|bar|MPa|order=flip|abbr=on}}, these animals burst when brought to the surface.{{cite web |url=https://montereybayaquarium.com |title=Giant siphonophore |archive-url=https://web.archive.org/web/19991128143839/https://montereybayaquarium.com/ |archive-date=1999-11-28 |url-status=dead |access-date=2020-05-10 }}{{Failed verification|date=January 2021}} 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 observed living Praya dubia during a systematic study of a water column, the animal's natural habitat, in Monterey Bay.[http://animaldiversity.ummz.umich.edu/site/accounts/classification/path/Praya_dubia.html Praya dubia, at the Animal Diversity Web] {{webarchive |url=https://web.archive.org/web/20080409234318/http://animaldiversity.ummz.umich.edu/site/accounts/classification/path/Praya_dubia.html |date=2008-04-09}}{{cite web |url=http://www.lifesci.ucsb.edu/~biolum/organism/pictures/praya.html |title=Prayid siphonophores |website=lifesci.ucsb.edu |access-date=2018-01-29}}{{cite web |url=https://ecologycenter.org/terrainmagazine/fall-2002/the-deep-next-door/ |title=The Deep Next Door {{!}} Ecology Center |website=ecologycenter.org |date=15 August 2002 |language=en-US |access-date=2018-01-29}}
Behavior
Praya dubia is an active swimmer that attracts its prey with bright blue bioluminescent light.{{cite web |url=http://biolum.eemb.ucsb.edu/ |title=The Bioluminescence Web Page |website=biolum.eemb.ucsb.edu |access-date=2018-01-29}} When it finds itself in a region abundant with food, it holds its position and deploys a curtain of tentacles covered with nematocysts which produce a powerful, toxic sting that can paralyze or kill prey that happen to bump into it.{{cite web |url=http://www.siphonophores.org/lures.php |title=Siphonophores |website=siphonophores.org |access-date=2018-01-29}} Praya dubia
A Praya dubia specimen, filmed in its native habitat, was featured in Episode 2 of the David Attenborough television series Blue Planet II, produced for the BBC.
References
{{Reflist}}
External links
- [https://www.youtube.com/watch?v=_EWYfedtLrc 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..
- [https://www.youtube.com/watch?v=8Vkn94C_iGk Deep sea siphonophore off Roatán Honduras - 2300 feet], YouTube, 10 June 2013, Roatán Institute of Deepsea Exploration, Accessed 28, January 2018.
- [http://www.iobis.org/mapper/?taxon_id=497295 Praya dubia Distribution Map at Ocean Biogeographic Information System]
- [http://eol.org/data_objects/32903561 Praya dubia Habitat at Encyclopedia of Life]
{{Taxonbar|from=Q2512355}}
Category:Cnidarians of the Atlantic Ocean
Category:Cnidarians of the Caribbean Sea
Category:Bioluminescent cnidarians
Category:Biota of the Gulf of Mexico
Category:Marine fauna of Europe