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''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 small, blue
sea slug Sea slug is a common name for some marine invertebrates with varying levels of resemblance to terrestrial slugs. Most creatures known as sea slugs are gastropods, i.e. they are sea snails (marine gastropod mollusks) that over evolutionary time ...
, a
pelagic The pelagic zone consists of the water column of the open ocean, and can be further divided into regions by depth (as illustrated on the right). The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or w ...
(open-ocean) aeolid nudibranch, a shell-less gastropod
mollusk Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000  extant species of molluscs are recognized. The number of fossil species is e ...
in the
family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...
Glaucidae. These sea slugs are
pelagic The pelagic zone consists of the water column of the open ocean, and can be further divided into regions by depth (as illustrated on the right). The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or w ...
; they float upside down by using the surface tension of the water to stay up, where they are carried along by the winds and ocean currents. ''G. atlanticus'' makes use of
countershading Countershading, or Thayer's law, is a method of camouflage in which an animal's coloration is darker on the top or upper side and lighter on the underside of the body. This pattern is found in many species of mammals, reptiles, birds, fish, a ...
: the blue side of their body faces upwards, blending in with the blue of the water. The silver/grey side of the sea slugs faces downwards, blending in with the sunlight reflecting on the ocean's surface when viewed facing upwards underwater. ''Glaucus atlanticus'' feed on other pelagic creatures, including the
Portuguese man o' war The Portuguese man o' war (''Physalia physalis''), also known as the man-of-war, is a marine hydrozoan found in the Atlantic Ocean and the Indian Ocean. It is considered to be the same species as the Pacific man o' war or blue bottle, which is ...
and other
venomous Venom or zootoxin is a type of toxin produced by an animal that is actively delivered through a wound by means of a bite, sting, or similar action. The toxin is delivered through a specially evolved ''venom apparatus'', such as fangs or a sti ...
siphonophores Siphonophorae (from Greek ''siphōn'' 'tube' + ''pherein'' 'to bear') is an order within Hydrozoa, which is a class of marine organisms within the phylum Cnidaria. According to the World Register of Marine Species, the order contains 175 specie ...
. This sea slug stores stinging 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, '' G. marginatus'', which is now understood to be not one species, but a
cryptic species complex In biology, a species complex is a group of closely related organisms that are so similar in appearance and other features that the boundaries between them are often unclear. The taxa in the complex may be able to hybridize readily with each oth ...
of four separate species that live in the Indian Ocean and Pacific Ocean. It shares the common name "blue dragon" with '' Pteraeolidia ianthina'' and ''G. marginatus''.


Description

At maturity ''G. atlanticus'' can be up to in length, though larger specimens have been found. It can live up to a year under the right conditions. 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.
Cerata :''The tortrix moth genus ''Cerata'' is considered a junior synonym of ''Cydia. Cerata, singular ceras, are anatomical structures found externally in nudibranch sea slugs, especially in aeolid nudibranchs, marine opisthobranch gastropod mollusks ...
, also known as papillae, extend laterally from three different pairs of peduncles. The papillae are placed in a single row (uniseriate) and may be up to 84 inches total, (Forster, 1777). ''Glaucus atlanticus'' is usually found in tropical/subtropical areas, floating at the ocean's surface due to the stored gulped air inside their stomachs. They usually feed on cnidarians, which can be noisy due to air escaping their stomachs as they feed. The radula of this species bears serrated teeth which, paired with a strong jaw and denticles, allows it to grasp and "chip down" parts of its prey.


Buoyancy and coloration

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 snail), and this has either a blue or blue-white coloration. The true
dorsal Dorsal (from Latin ''dorsum'' ‘back’) may refer to: * Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism * Dorsal, positioned on top of an aircraft's fuselage * Dorsal c ...
surface (carried downwards in ''G. atlanticus'') is completely silver-grey. This coloration is an example of
countershading Countershading, or Thayer's law, is a method of camouflage in which an animal's coloration is darker on the top or upper side and lighter on the underside of the body. This pattern is found in many species of mammals, reptiles, birds, fish, a ...
, which helps protect it from predators that might attack from below and from above. The blue coloration is also thought to reflect harmful UV sunlight.


Distribution and habitat

This nudibranch is
pelagic The pelagic zone consists of the water column of the open ocean, and can be further divided into regions by depth (as illustrated on the right). The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or w ...
, and there is some evidence that it occurs throughout the world's oceans, in temperate and tropical waters. It has been recorded from the east and south coasts of South Africa, European waters, the east coast of Australia, and Mozambique. The ''G. atlanticus'' species geographical range increased northward by 150 km in the Gulf of California. Since the middle of the 19th century, records of this species have been reported on the
Azores ) , motto =( en, "Rather die free than subjected in peace") , anthem= ( en, "Anthem of the Azores") , image_map=Locator_map_of_Azores_in_EU.svg , map_alt=Location of the Azores within the European Union , map_caption=Location of the Azores wi ...
. ''Glaucus 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 environments. Before finding ''G. atlanticus'' off Andhra Pradesh, these nudibranchs were documented as having been seen in the
Bay of Bengal The Bay of Bengal is the northeastern part of the Indian Ocean, bounded on the west and northwest by India, on the north by Bangladesh, and on the east by Myanmar and the Andaman and Nicobar Islands of India. Its southern limit is a line betwee ...
and off the coast of Tamil Nadu, India, over 677 kilometers apart.
''Glaucus atlanticus'' was also recently found off Bermuda in January 2016, and uncommonly washes ashore on east coast beaches at Barbados, Lesser Antilles. Although these sea slugs live on the open ocean, they sometimes accidentally wash up onto the shore, and therefore they may be found on beaches. In April 2022, specimens were found in the Gulf of Mexico along the Texas coast.


Life history and behavior

''Glaucus atlanticus'' preys on other larger pelagic organisms. The sea slugs can move toward prey or mates by using their cerata to make slow swimming movements. They are known to prey on the dangerously
venom Venom or zootoxin is a type of toxin produced by an animal that is actively delivered through a wound by means of a bite, sting, or similar action. The toxin is delivered through a specially evolved ''venom apparatus'', such as fangs or a st ...
ous
Portuguese man o' war The Portuguese man o' war (''Physalia physalis''), also known as the man-of-war, is a marine hydrozoan found in the Atlantic Ocean and the Indian Ocean. It is considered to be the same species as the Pacific man o' war or blue bottle, which is ...
(''Physalia physalis''); the by-the-wind-sailor (''
Velella velella ''Velella'' is a monospecific genus of hydrozoa in the Porpitidae family. Its only known species is ''Velella velella'', a cosmopolitan free-floating hydrozoan that lives on the surface of the open ocean. It is commonly known by the names sea r ...
''); the blue button (''
Porpita porpita ''Porpita porpita'', or blue button, is a marine organism consisting of a colony of hydroids found in the warmer, tropical and sub-tropical waters of the Pacific, Atlantic, and Indian oceans, as well as the Mediterranean Sea and eastern Arabian ...
''); 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
venom Venom or zootoxin is a type of toxin produced by an animal that is actively delivered through a wound by means of a bite, sting, or similar action. The toxin is delivered through a specially evolved ''venom apparatus'', such as fangs or a st ...
ous nematocysts. The slug consumes chunks of the organism and appears to select and store the most venomous nematocysts for its own use against future prey. The nematocysts are collected in specialized sacs (
cnidosac A cnidosac is an anatomical feature that is found in the group of sea slugs known as aeolid nudibranchs, a clade of marine opisthobranch gastropod molluscs. A cnidosac contains cnidocytes, stinging cells that are also known as cnidoblasts or n ...
s) at the tip of the animal's
cerata :''The tortrix moth genus ''Cerata'' is considered a junior synonym of ''Cydia. Cerata, singular ceras, are anatomical structures found externally in nudibranch sea slugs, especially in aeolid nudibranchs, marine opisthobranch gastropod mollusks ...
, the thin feather-like "fingers" on its body. Because ''G. atlanticus'' concentrates the venom, it can produce a more powerful and deadly sting than the man o' war on which it feeds. Like almost all
heterobranch Heterobranchia, the ''heterobranchs'' (meaning "different-gilled snails"), is a taxonomic clade of snails and slugs, which includes marine, aquatic and terrestrial gastropod mollusks. Heterobranchia is one of the main clades of gastropods. Cur ...
s, blue dragons are
hermaphrodites In reproductive biology, a hermaphrodite () is an organism that has both kinds of reproductive organs and can produce both gametes associated with male and female sexes. Many taxonomic groups of animals (mostly invertebrates) do not have sep ...
and their male reproductive organs have evolved to be especially large and hooked to avoid their partner's venomous cerata. Unlike most
nudibranch Nudibranchs () are a group of soft-bodied marine gastropod molluscs which shed their shells after their larval stage. They are noted for their often extraordinary colours and striking forms, and they have been given colourful nicknames to match, ...
s, which mate with their right sides facing, sea swallows mate with ventral sides facing. 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. On average, ''G. atlanticus'' can lay 55 egg strings per hour. Studies have indicated that the ''G. atlanticus'' is not globally 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.


Sting

''Glaucus atlanticus'' is able to swallow the venomous nematocysts from
siphonophore Siphonophorae (from Greek ''siphōn'' 'tube' + ''pherein'' 'to bear') is an order within Hydrozoa, which is a class of marine organisms within the phylum Cnidaria. According to the World Register of Marine Species, the order contains 175 specie ...
s such as the
Portuguese man o' war The Portuguese man o' war (''Physalia physalis''), also known as the man-of-war, is a marine hydrozoan found in the Atlantic Ocean and the Indian Ocean. It is considered to be the same species as the Pacific man o' war or blue bottle, which is ...
, and store them in the extremities of its finger-like
cerata :''The tortrix moth genus ''Cerata'' is considered a junior synonym of ''Cydia. Cerata, singular ceras, are anatomical structures found externally in nudibranch sea slugs, especially in aeolid nudibranchs, marine opisthobranch gastropod mollusks ...
. Picking up the animal can result in a painful sting, with symptoms similar to those caused by the Portuguese man o' war. The symptoms that may appear after being stung are
nausea Nausea is a diffuse sensation of unease and discomfort, sometimes perceived as an urge to vomit. While not painful, it can be a debilitating symptom if prolonged and has been described as placing discomfort on the chest, abdomen, or back of the ...
, pain,
vomiting Vomiting (also known as emesis and throwing up) is the involuntary, forceful expulsion of the contents of one's stomach through the mouth and sometimes the nose. Vomiting can be the result of ailments like food poisoning, gastroenteri ...
, acute allergic contact dermatitis,
erythema Erythema (from the Greek , meaning red) is redness of the skin or mucous membranes, caused by hyperemia (increased blood flow) in superficial capillaries. It occurs with any skin injury, infection, or inflammation. Examples of erythema not asso ...
, urticarial papules, potential
vesicle Vesicle may refer to: ; In cellular biology or chemistry * Vesicle (biology and chemistry) In cell biology, a vesicle is a structure within or outside a cell, consisting of liquid or cytoplasm enclosed by a lipid bilayer. Vesicles form nat ...
formation and post-inflammatory hyperpigmentation.


References


Further reading

* * *


External links


Sea Slug Forum
* * {{taxonbar, from=Q131757 Glaucidae Molluscs described in 1777