''Pteraeolidia ianthina'' is a

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 t ...

, an aeolid

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 matc ...

in the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Facelinidae The Facelinidae are a Taxonomy (biology), taxonomic family (biology), family of colorful sea slugs. These are specifically aeolid nudibranchs. They are marine (ocean), marine gastropod molluscs.Bouchet, P. (2012). Facelinidae. Accessed through: W ...

.Bouchet P. & Rocroi J.-P. (Ed.); Frýda J., Hausdorf B., Ponder W., Valdes A. & Warén A. 2005. ''Classification and nomenclator of gastropod families''. Malacologia: International Journal of Malacology, 47(1-2). ConchBooks: Hackenheim, Germany. . ISSN 0076-2997. 397 pp. http://www.vliz.be/Vmdcdata/imis2/ref.php?refid=78278Rosenberg, G. (2012). Pteraeolidia ianthina. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=213527 on 1 September 2012 It is known as a blue dragon, a name it shares with ''

Glaucus atlanticus ''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, a pelagic (open-ocean) aeolid nudibran ...

'' and ''

Glaucus marginatus ''Glaucus marginatus'' is a species of small, floating, blue sea slug; a pelagic (open-ocean) aeolid nudibranch; a marine opisthobranch gastropod mollusc in the family Glaucidae.Valdés A. & Campillo O.A. (2004) ''Systematics of pelagic aeo ...

''.

Distribution

This species is widespread throughout the Indo-Pacific. Recent research shows that it is a complex of more than one species.

Description

''Pteraeolidia ianthina'', one of the most common aeolids found, is often called a "blue dragon" by

Eastern Australia The eastern states of Australia are the states adjoining the east continental coastline of Australia. These are the mainland states of Victoria, New South Wales and Queensland, and the island state of Tasmania. The Australian Capital Territory ...

n divers because of its close resemblance to a

Chinese dragon The Chinese dragon, also known as ''loong'', ''long'' or ''lung'', is a legendary creature in Chinese mythology, Chinese folklore, and Chinese culture at large. Chinese dragons have many Outline of life forms, animal-like forms such as Bixi (my ...

. It is one of the most common aeolid nudibranchs found in Eastern Australia, and can inflict a painful sting to humans. The body color of this species is translucent tan, but the

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 ...

, which vary from dark purple to lavender to golden brown, give the

most of its distinct color. Green specimens are not uncommon. The slug is elongated () with many clusters of medium-large sized cerata along the length of the body. The fat

rhinophore A rhinophore is one of a pair of chemosensory club-shaped, rod-shaped or ear-like structures which are the most prominent part of the external head anatomy in sea slugs, marine gastropod opisthobranch mollusks such as the nudibranchs, sea har ...

s and the long cephalic tentacles have at least two dark purple bands that stand out. The tips of the cerata contain

nematocyst A cnidocyte (also known as a cnidoblast or nematocyte) is an explosive cell containing one large secretory organelle called a cnidocyst (also known as a cnida () or nematocyst) that can deliver a sting to other organisms. The presence of this ce ...

s. Algal

zooxanthellae Zooxanthellae is a colloquial term for single-celled dinoflagellates that are able to live in symbiosis with diverse marine invertebrates including demosponges, corals, jellyfish, and nudibranchs. Most known zooxanthellae are in the genus ''Sy ...

of the genus ''

Symbiodinium : ''This is about the genus sometimes called Zoox. For the company, see Zoox (company)'' ''Symbiodinium'' is a genus of dinoflagellates that encompasses the largest and most prevalent group of endosymbiotic dinoflagellates known. These unicellul ...

'' derived from the food of these animals continue to photosynthesise inside the body and give rise to brown and green pigments. ''Symbiodinium'', together with the nematocysts, are presumed to be derived from

coelenterate Radiata or Radiates is a historical taxonomic rank that was used to classify animals with radially symmetric body plans. The term Radiata is no longer accepted, as it united several different groupings of animals that do not form a monophyletic ...

prey. These ''Symbiodinium'' occur within

vacuole A vacuole () is a membrane-bound organelle which is present in plant and fungal cells and some protist, animal, and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water containing inorganic and organic mo ...

s in host cells derived from the

endoderm Endoderm is the innermost of the three primary germ layers in the very early embryo. The other two layers are the ectoderm (outside layer) and mesoderm (middle layer). Cells migrating inward along the archenteron form the inner layer of the gast ...

. Young specimens are much shorter, have fewer cerata, and are often mistaken for other nudibranch species.Cory Pittman and Pauline Fiene, 2015
''Pteraeolidia semperi''
Sea slugs of Hawaii

Symbiosis with dinoflagellates

This sea slug feeds on

hydroids Hydroids are a life stage for most animals of the class Hydrozoa, small predators related to jellyfish. Some hydroids such as the freshwater '' Hydra'' are solitary, with the polyp attached directly to the substrate. When these produce buds ...

which contain ''

'', microscopic

dinoflagellates The dinoflagellates (Greek δῖνος ''dinos'' "whirling" and Latin ''flagellum'' "whip, scourge") are a monophyletic group of single-celled eukaryotes constituting the phylum Dinoflagellata and are usually considered algae. Dinoflagellates are ...

that are

photosynthetic Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in c ...

. The microscopic ''Symbiodinium'' acquired from the hydroids are 'farmed' in the sea slug's digestive diverticula, where the ''Symbiodinium'' photosynthesizes sugars to be used by the slug. The slug gains enough photosythetically derived sugars to sustain it without feeding.

Distribution

Description

Symbiosis with dinoflagellates

References

Further reading