Glaucus atlanticus

{{short description|Species of mollusc}} {{Use dmy dates|date=May 2020}} {{Use British English|date=May 2026}} {{About|the sea animal|other uses|Blue Dragon (disambiguation){{!}}Blue Dragon}} {{pp-pc}} {{Speciesbox | image = Glaucus_atlanticus_1_cropped.jpg | image_caption = | taxon = Glaucus atlanticus | authority = [[Georg Forster|Forster]], 1777 | synonyms = * ''Doris radiata'' Gmelin, 1791 (synonym) * ''Glaucus distichoicus'' d'Orbigny, 1837 * ''Glaucus flagellum'' Blumenblach, 1803 (synonym) * ''Glaucus hexapterigius'' Cuvier, 1805 (synonym) * ''Glaucus lineatus'' Reinhardt & Bergh, 1864 * ''Glaucus longicirrhus'' Reinhardt & Bergh, 1864 | synonyms_ref = <ref name=WoRMS/> }}

'''''Glaucus atlanticus''''' (common names include the '''blue sea dragon''', '''sea swallow''', '''blue angel''', '''blue glaucus''', '''dragon slug''', '''blue dragon''', '''blue sea slug''', and '''blue ocean slug''') is a [[species]] of [[sea slug]] in the family [[Glaucidae]].<ref>{{cite book |last1=Lalli |first1=C. M. |last2=Gilmer |first2=R. W. |year=1989 |title=Pelagic snails: the biology of holoplanktonic gastropod mollusks |publisher=Stanford University Press |isbn=978-0-8047-1490-7 |url=https://books.google.com/books?id=yIAfwz5cxPMC |page=224 }}</ref>

These sea slugs live in the [[pelagic zone]] (open ocean), where they float upside-down by using the [[surface tension]] of the water to stay afloat. In addition, they have a gas bubble in their stomach that makes it easier for them to float.<ref>{{Cite journal |last=[[Johanna Segovia|Segovia]] |first=Johanna |last2=López |first2=Gina |date=2015 |title=Registro de Glaucus atlanticus en la costa de El Salvador, Pacíficode Centroamérica |url=https://revista.ib.unam.mx/index.php/bio/article/view/1519 |journal=Revista Mexicana de Biodiversidad |language=es |volume=86 |issue=4 |doi=10.1016/j.rmb.2015.05.015 |issn=2007-8706|doi-access=free }}</ref> They are carried along by the winds and ocean currents. ''G. atlanticus'' makes use of [[countershading]]; the blue side of their bodies faces upwards, blending in with the blue of the water. The silver-grey dorsal side of the sea slug faces downwards, blending in with the sunlight shining through the ocean's surface when viewed from below the surface of the water.

''G. atlanticus'' feeds on other pelagic creatures, including the [[Portuguese man o' war]] and other [[venom]]ous [[Siphonophorae|siphonophores]]. This sea slug stores stinging [[Cnidocyte|nematocysts]] from the siphonophores within its own tissues as defence against predators. Humans handling the slug may receive a very painful and potentially dangerous sting.

==Taxonomy== This species looks similar to, and is closely related to, ''[[Glaucus marginatus|G. marginatus]]'', which is now understood to be not one species, but a [[sibling species|cryptic species complex]] of four separate species that live in the Indian and Pacific Oceans.<ref name=WoRMS>{{WoRMS |id=138033 |title=Glaucus |access-date=5 August 2012}}</ref><ref name=churchill>{{cite journal |title=Molecular and morphological systematics of neustonic nudibranchs (Mollusca: Gastropoda: Glaucidae: ''Glaucus''), with descriptions of three new cryptic species |journal=Invertebrate Systematics |volume=28 |issue=2 |page=174 |doi=10.1071/IS13038 |year=2014 |last1=Churchill |first1=Celia K. C. |last2=Valdés |first2=Ángel |last3=ó Foighil |first3=Diarmaid |s2cid=84010907 }}</ref> It shares the common name "blue dragon" with ''[[Pteraeolidia ianthina]]''<ref name=ssf>{{cite web |last1=Rudman |first1=W. B. |title=Pteraeolidia ianthina (Angas,1864) |publisher=[[Australian Museum]] |url=http://www.seaslugforum.net/factsheet/pteriant |website=The Sea Slug Forum |access-date=13 Feb 2021 |date=15 July 2010}}</ref> and ''G. marginatus''.<ref>{{cite web |last=Salleh |first=Anna |website=ABC News |title=Bizarre 'blue fleet' blows onto Australia's east coast |publisher=[[Australian Broadcasting Corporation]] |date=12 February 2021 |url=https://www.abc.net.au/news/science/2021-02-13/bizarre-blue-fleet-blows-onto-australias-east-coast/13139456 |access-date=13 February 2021}}</ref>

== Description == At maturity, ''G. atlanticus'' is usually around {{convert|3|cm|in|abbr=on}} long,<ref>{{cite web |url=http://www.nhm.ac.uk/nature-online/species-of-the-day/collections/our-collections/glaucus-atlanticus/taxonomy/index.html |title=''Glaucus atlanticus'' (blue sea slug) |publisher=The Natural History Museum |access-date=2013-04-13 |archive-url=https://web.archive.org/web/20150627143813/http://www.nhm.ac.uk/nature-online/species-of-the-day/collections/our-collections/glaucus-atlanticus/taxonomy/index.html |archive-date=2015-06-27 }}</ref> although larger specimens have been found.<ref name="RTP">{{cite web |title=Dragão Azul do Mar |url=https://www.rtp.pt/acores/local/dragao-azul-do-mar-ou-lesma-do-mar-e-inofensivo-para-as-pessoas-video_54644 |publisher=[[Rádio e Televisão de Portugal|RTP]] |access-date=14 November 2020 |archive-date=17 November 2021 |archive-url=https://web.archive.org/web/20211117041022/https://www.rtp.pt/acores/local/dragao-azul-do-mar-ou-lesma-do-mar-e-inofensivo-para-as-pessoas-video_54644 }}</ref> It can live for up to a year under the right conditions.<ref name="SMNH">{{cite web |title=Blue Dragons of the Sea |url=https://nmnh.typepad.com/no_bones/2015/05/blue-dragons-of-the-sea.html |archive-url=https://web.archive.org/web/20201116083549/https://nmnh.typepad.com/no_bones/2015/05/blue-dragons-of-the-sea.html |archive-date=16 November 2020 |access-date=14 November 2020 |publisher=[[Smithsonian Museum of Natural History]] |url-status=bot: unknown }}</ref> It is silvery grey on its dorsal side and dark and pale blue ventrally. It has dark blue stripes on its head. It has a flat, tapering body and six appendages that branch out into rayed, finger-like cerata.<ref>{{cite book |last1=Piper |first1=R. |year=2007 |title=Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals |publisher=Greenwood Publishing Group |isbn=978-0-313-33922-6 |pages=[https://archive.org/details/extraordinaryani0000pipe/page/42 42–43] |url=https://archive.org/details/extraordinaryani0000pipe/page/42 }}</ref>

The first pair of [[cerata]], also known as papillae, extends laterally from peduncles with a short stalk, while the other two groups are sessile. The most dorsal cerata in a group is largest and other cerata decreases in size ventrally. The anterior corners of the foot (the dorsal side) are rounded. The centre of the foot is silver in colour, and the outer edge varies from dark blue to brown.<ref name="churchill" /> The papillae are placed in a single row (uniseriate) and may number up to 84 in total (unlike over one another as in ''[[Glaucus marginatus|G. marginatus]]'').<ref name="Srinivasulu et al. 2012"/>

''G. atlanticus'' is usually found in tropical/subtropical areas, floating at the ocean's surface due to the stored gulped air inside its stomach. It usually feeds on [[cnidaria]]ns, which can be noisy due to air escaping its stomach as it feeds.<ref name="Churchill et al. 2014"/><ref name="Helm et al. 2021">{{Cite journal |last=Helm |first=Rebecca R. |date=2021-12-14 |title=Natural history of neustonic animals in the Sargasso Sea: reproduction, predation, and behavior of ''Glaucus atlanticus'', ''Velella velella'', and ''Janthina'' spp. |journal=Marine Biodiversity |language=en |volume=51 |issue=6 |page=99 |doi=10.1007/s12526-021-01233-5 |s2cid=245186096 |doi-access=free |bibcode=2021MarBd..51...99H }}</ref><ref name="Pinotti et al. 2019">{{Cite journal |last1=Pinotti |first1=Raphael M. |last2=Bom |first2=Fabio C. |last3=Muxagata |first3=Erik |date=2019-04-08 |title=On the occurrence and ecology of ''Glaucus atlanticus'' Forster, 1777 (Mollusca: Nudibranchia) along the Southwestern Atlantic coast |journal=Anais da Academia Brasileira de Ciências |language=en |volume=91 |issue=1 |article-number=e20180154 |doi=10.1590/0001-3765201920180154 |pmid=30994760 |s2cid=119501907 |doi-access=free }}</ref>

The [[radula]] of this species bears serrated teeth,<ref name="Thompson2008">{{Cite journal |last1=Thompson |first1=T. E. |last2=McFarlane |first2=I. D. |doi=10.1111/j.1095-8312.1967.tb00967.x |title=Observations on a collection of ''Glaucus'' from the Gulf of Aden with a critical review of published records of Glaucidae (Gastropoda, Opisthobranchia) |journal=Proceedings of the Linnean Society of London |volume=178 |issue=2 |pages=107–123 |year=2008 }}</ref> which paired with a strong jaw and denticles, allows it to grasp and "chip down" parts of its prey.<ref name="SMNH" />

==Buoyancy and colouration== {{see also|Ocean surface ecosystem}}

With the aid of a gas-filled sac in its stomach, ''G. atlanticus'' floats at the surface. Due to the location of the gas sac, this species floats upside down. The upper surface is actually the foot (the underside in other slugs and snails), and this has either a blue or blue-white coloration. The true [[Dorsum (anatomy)|dorsal]] surface (carried downwards in ''G. atlanticus'') is completely silver-grey. This coloration is an example of [[countershading]], which helps protect it from predators that might attack from below and from above.<ref>{{cite web |url=http://bluedragonslug.weebly.com/habitat.html |title=Habitat – Glaucus Atlanticus |publisher=Bluedragonslug.weebly.com |access-date=2018-03-14}}</ref> The blue coloration is also thought to reflect harmful [[ultraviolet]] sunlight.

== Distribution and habitat == [[File:Glaucus atlant..jpg|thumb|left|''Glaucus atlanticus'' is the blue sea slug shown here out of water on a beach, and thus collapsed; however, touching the animal directly with your skin can result in a painful sting, with symptoms similar to those caused by the [[Portuguese man o' war]]]] [[File:Blue_dragon-glaucus_atlanticus_(8599051974).jpg|thumb|left|The slug in the water]]

===Habitat=== This [[nudibranch]] is [[Pelagic zone|pelagic]], and some evidence indicates that it occurs throughout the world's oceans, in temperate and tropical waters. Although these sea slugs live on the open ocean, they sometimes accidentally wash up onto the shore, so they may be found on beaches.<ref name="Srinivasulu et al. 2012" /> Along the Brazilian Coast, the distribution of ''G. atlanticus'' is shaped by the [[Brazil Current]] and seasonal shifts in the [[Subtropical convergence|Subtropical Convergence Zone]], specifically during [[El Niño–Southern Oscillation|El Niño]] events. These ocean currents and shifts in the weather can push the species toward the shore, ultimately causing seasonal strandings.<ref>{{Cite web|url=https://www.scielo.br/j/aabc/a/RRQPD6w8XGtXPNFcqQG635g/?lang=en|title=On the occurrence and ecology of Glaucus atlanticus Forster, 1777 (Mollusca: Nudibranchia) along the Southwestern Atlantic coast|website=www.scielo.br}}</ref>

===Distribution=== It has been recorded from the east and south coasts of South Africa, European waters, the east coast of Australia, and Mozambique.<ref name=churchill/> With recent sightings in Central America and South Asia.

Since the middle of the 19th century, records of this species have been reported on the [[Azores]].<ref name="RTP" />

''G. atlanticus'' was recently found in the [[Humboldt Current]] ecosystem in Peru in 2013, and off [[Andhra Pradesh]] in India in 2012. This is in line with the known habitat characteristics of the species; they thrive in warm, temperate climates in the Southern Pacific, and in circumtropical and [[Lusitanian distribution|Lusitanian environments]]. Before finding ''G. atlanticus'' off Andhra Pradesh, these nudibranchs were documented as having been seen in the [[Bay of Bengal]] and off the coast of [[Tamil Nadu]], India, over 677 km apart.<ref>{{cite journal |last1=Uribe |first1=Roberto A. |last2=Nakamura |first2=Katia |last3=Indacochea |first3=Aldo |last4=Pacheco |first4=Aldo S. |last5=Hooker |first5=Yuri |last6=Schrödl |first6=Michael |title=A review on the diversity and distribution of opisthobranch gastropods from Peru, with the addition of three new records |journal=Spixiana |date=September 2013 |volume=36 |issue=341–8391 |pages=43–60 |url=https://www.researchgate.net/publication/256446985 |access-date=24 October 2014}}</ref>

Observations in 2015 and 2016 suggested that the ''G. atlanticus'' species' geographical range had increased northward by 150 km in the [[Gulf of California]] in Central America compared with previous sightings.<ref>{{cite journal |url=https://www.researchgate.net/publication/325213184 |doi=10.4003/006.036.0113 |title=Occurrence of ''Glaucus atlanticus'' in the Midriff Islands Region, Gulf of California, Mexico |year=2018 |last1=Hernández |first1=Luis |last2=Munguía-Vega |first2=Adrián |last3=Pérez-Alarcón |first3=Fernanda |last4=Fernández-Rivera-Melo |first4=Francisco J. |last5=Angulo-Campillo |first5=Orso |journal=American Malacological Bulletin |volume=36 |pages=145–149 |s2cid=89794645}}</ref> ''G. atlanticus'' was also found off [[Bermuda]] in January 2016,<ref>{{cite news |title=Diver finds 'blue dragons' at Spittal Pond |first=Owain |last=Johnston-Barnes |work=The Royal Gazette |date=25 January 2016 |url=http://www.royalgazette.com/article/20160125/NEWS/160129767/diver-finds-blue-dragons-at-spittal-pond}}</ref> and uncommonly washes ashore on east coast beaches at [[Barbados]], Lesser Antilles.

In April 2022, specimens were found in the [[Gulf of Mexico]] along the [[Texas]] coast, USA.<ref>{{cite news |title=Don't Touch: Rare blue dragons are showing up on Texas beaches again |first=Mary Claire |last=Patton |work=KSAT 12 |date=11 April 2022 |url=https://www.ksat.com/news/texas/2022/04/11/dont-touch-rare-blue-dragons-are-showing-up-on-texas-beaches-again/}}</ref> On 31 August 2023 and 11 July 2025, blue sea slugs were reported to be found along [[Karon Beach]], Phuket, Thailand.<ref>{{Cite news |title=Venomous 'blue dragon' found on Phuket beach |language=en |work=Bangkok Post |date=31 August 2023 |url=https://www.bangkokpost.com/thailand/general/2639390/venomous-blue-dragon-found-on-phuket-beach |access-date=2023-09-01}}</ref><ref>{{Cite web |last=Petpailin |first=Petch |date=2023-08-31 |title=Beach warning: Venomous blue dragon sea slug spotted in Phuket |url=https://thethaiger.com/news/national/beach-warning-venomous-blue-dragon-sea-slug-spotted-in-phuket |access-date=2023-09-01 |website=Thaiger |language=en}}</ref><ref>{{Cite news |title=Venomous Blue Dragon sea slugs spotted on Phuket beach |language=en |work=Bangkok Post |date=11 July 2025 |url=https://www.bangkokpost.com/thailand/general/3067349/venomous-blue-dragon-sea-slugs-spotted-on-phuket-beach |access-date=2025-07-16}}</ref>

On 31 July and 12 August 2025, specimens were spotted on the beaches of [[Lanzarote]].<ref>{{Cite web|url=https://www.lavozdelanzarote.com/actualidad/sucesos/cierran-playa-garita-en-arrieta-por-presencia-dragones-azules_237049_102.html|title=Cierran la playa de La Garita, en Arrieta, por la presencia de dragones azules|date=12 August 2025|website=La Voz de Lanzarote}}</ref><ref>{{Cite web|url=https://rtvc.es/encuentran-ejemplares-dragon-azul-playa-famara-28-julio-2025/|title=Encuentran ejemplares del dragón azul en la Playa de Famara|first=RTVC /|last=EFE|date=28 July 2025}}</ref> On 20 and 21 August 2025, specimens were also spotted on two beaches in [[Alicante]], Spain; on the beach of [[Guardamar del Segura]], which resulted in the closure of the beach<ref>{{Cite web |last=Cuquerella |first=Toni |date=2025-08-21 |title=Guardamar prohíbe el baño en todas sus playas por la presencia de la especie venenosa 'dragón azul' |url=https://www.eldiario.es/comunitat-valenciana/comarcas/guardamar-prohibe-bano-playas-presencia-especie-venenosa-dragon-azul_1_12548062.html |access-date=2025-08-21 |website=ElDiario.es |language=es}}</ref> for several hours, as well as on the beach of La Mata, in [[Torrevieja]].<ref>{{Cite web |last=Gil |first=Elisa |date=2025-08-21 |title=Hallado un tercer "dragón azul" en la playa de La Mata |url=https://vegabajadigital.com/hallado-un-tercer-dragon-azul-en-la-playa-de-la-mata/ |access-date=2025-08-21 |website=Vegabajadigital |language=es}}</ref>

== Life history and behaviour == ''G. atlanticus'' [[predation|preys]] on other larger pelagic organisms. The sea slugs can move toward prey or mates by using their [[cerata]], the thin feather-like "fingers" on its body, to make slow swimming movements.<ref name="Srinivasulu et al. 2012">{{cite journal |last1=Srinivasulu |first1=Bhargavi |last2=Srinivasulu |first2=C. |last3=Kumar |first3=G. Chethan |year=2012 |title=First record of the blue sea slug (''Glaucus atlanticus'') from Andhra Pradesh–India |journal=Taprobanica: The Journal of Asian Biodiversity |volume=4 |issue=1 |pages=52–53 |doi=10.4038/tapro.v4i1.4386 |doi-access=free }}</ref><ref>MacLellan, Amelia "''Glaucus atlanticus'' (blue sea slug)". The Natural History Museum. Retrieved 2013-04-13</ref> They are known to prey on the dangerously [[venom]]ous Portuguese man o' war (''[[Portuguese man o' war|Physalia physalis]]''), the by-the-wind-sailor (''[[Velella|Velella velella]]''), the blue button (''[[Porpita porpita]]''), and the violet snail, ''[[Janthina janthina]]''. Occasionally, individuals attack and eat other individuals in captivity.

The species is able to feed on the [[Portuguese man o' war]] due to its immunity to the venomous [[nematocyst]]s. The slug consumes chunks of the organism and appears to select and store the most venomous nematocysts for its own use against future prey in a process called [[kleptocnidy]].<ref>{{Cite web |title=Rare blue dragons are washing up on the Padre Island National Seashore |url=https://www.cnn.com/2020/05/09/us/blue-dragon-padre-island-national-seashore-trnd/index.html |first=Leah |last=Asmelash |website=CNN |date=9 May 2020 |access-date=2020-05-11}}</ref> The nematocysts are collected in specialised sacs ([[cnidosac]]s) at the tip of the animal's cerata. Because ''G. atlanticus'' concentrates the venom, it can produce a more powerful and deadly sting than the man o' war on which it feeds.<ref name="rudman-1998">{{cite web |author-link=William B. Rudman |last=Rudman |first=W. B. |date=6 November 1998 |url=http://www.seaslugforum.net/find/glauatla |title=''Glaucus atlanticus'' Forster, 1777 |work=Sea Slug Forum |access-date=26 February 2011 }}</ref>

Like almost all [[heterobranch]]s, blue dragons are [[hermaphrodites]] and their male reproductive organs have evolved to be especially large and hooked to avoid their partner's venomous cerata.<ref name="SMNH" /> Unlike most nudibranchs, which mate with their right sides facing, sea swallows mate with ventral sides facing.<ref>{{cite book |last1=Debelius |first1=H. |last2=Kuiter |first2=R. H. |year=2007 |title=Nudibranchs of the world |publisher=IKAN-Unterwasserarchiv |isbn=978-3-939767-06-0 }}</ref> After mating, both individuals are able to lay eggs and can release up to 20 on an egg string, often laying them in wood pieces or carcasses.<ref name="SMNH" /> On average, ''G. atlanticus'' can lay 55 egg strings per hour.<ref name="Helm et al. 2021"/> ''G. atlanticus'' is not globally [[Panmixia|panmictic]], but is localized within ocean basins. Gene flow among Afro-Eurasian and American populations is thus hindered by physical obstructions and water temperatures in the Arctic and Southern Oceans.<ref name="Churchill et al. 2014">{{Cite journal |last1=Churchill |first1=Celia K. C. |last2=Valdés |first2=Ángel |last3=Ó Foighil |first3=Diarmaid |date=2014-04-01 |title=Afro-Eurasia and the Americas present barriers to gene flow for the cosmopolitan neustonic nudibranch ''Glaucus atlanticus'' |journal=Marine Biology |volume=161 |issue=4 |pages=899–910 |doi=10.1007/s00227-014-2389-7 |bibcode=2014MarBi.161..899C |s2cid=84153330}}</ref>

== Sting == ''G. atlanticus'' can swallow the venomous nematocysts from [[siphonophore]]s, such as the [[Portuguese man o' war]], and store them in the extremities of its finger-like cerata in a process called [[kleptocnidy]].<ref name="rudman-1998" /> Picking up the animal can result in a painful sting, with symptoms similar to those caused by the Portuguese man o' war.<ref>{{cite news |title=Aquatic antagonists: Indirect nematocyst envenomation and acute allergic contact dermatitis due to nudibranchs |first=Patrick Thomas |last=Ottuso |work=Cutis |volume=83 |date=May 2009 |url=http://faculty.wwu.edu/shulld/esci%20432/NudibranchOttuso2009.pdf |access-date=27 April 2015 |archive-date=23 July 2021 |archive-url=https://web.archive.org/web/20210723000944/http://faculty.wwu.edu/shulld/esci%20432/NudibranchOttuso2009.pdf }}</ref> The symptoms that may appear after being stung are [[nausea]], [[pain]], [[vomiting]], [[Allergic contact dermatitis|acute allergic contact dermatitis]], [[erythema]], [[Papule|urticarial papules]], potential [[Vesicle (dermatology)|vesicle]] formation, and [[postinflammatory hyperpigmentation]].<ref name="Pinotti et al. 2019"/>

== References == {{Reflist|30em}}

== Further reading == * {{cite journal |last=Valdés |first=Ángel |author2=Orso Angulo Campillo |date=November 2004 |title=Systematics of Pelagic Aeolid Nudibranchs of the Family Glaucidae (Mollusca, Gastropoda) |journal=Bulletin of Marine Science |volume=75 |pages=381–389 |issue=3 |ref=none}} * {{cite journal|last1=MILLER|first1=M. C.|title=Aeolid nudibranchs (Gastropoda: Opisthobranchia) of the family Glaucidae from New Zealand waters|journal=Zoological Journal of the Linnean Society|date=January 1974|volume=54|issue=1|pages=31–61|doi=10.1111/j.1096-3642.1974.tb00792.x|ref=none}}

== External links == {{commons category|Glaucus atlanticus}} * [http://www.seaslugforum.net/find/glauatla Sea Slug Forum] * {{EOL}} * {{cite web|title=Blue Sea slug: Glaucus Atlanticus, Gold Coast, Australia|date=17 November 2017|website=YouTube|url=https://www.youtube.com/watch?v=aiYyo3PBs20 |archive-url=https://ghostarchive.org/varchive/youtube/20211219/aiYyo3PBs20 |archive-date=2021-12-19 |url-status=live}}{{cbignore}}

[[Category:Glaucus (gastropod)|atlanticus]] [[Category:Molluscs of the Atlantic Ocean]] [[Category:Molluscs of the Indian Ocean]] [[Category:Molluscs of the Pacific Ocean]] [[Category:Taxa named by Georg Forster]] [[Category:Gastropods described in 1777]]