Pteraeolidia ianthina, one of the most common aeolids found, is often called a "blue dragon" by Eastern Australian divers because of its close resemblance to a Chinese dragon. It is one of the most common aeolid nudibranchs found in Eastern Australia. It can inflict a painful sting to humans.
The body color of this species is translucent tan, but the cerata, which vary from dark purple to lavender to golden brown, give the nudibranch most of its distinct color, green specimens are not uncommon.
The slug is very elongated (7 cm) with many clusters of medium-large sized cerata along the length of the body. The fat rhinophores and the long cephalic tentacles have at least two dark purple bands that stand out. The tips of the cerata contain nematocysts.
Symbiotic zooxanthellae continue to photosynthesise inside the body and give rise to brown and green pigments. The zooxanthellae, together with the nematocysts, are presumed to be derived from coelenterate prey. These zooxanthellae occur within vacuoles in host cells derived from the endoderm.
This sea slug has evolved the ability to harness the sun's energy for its own use. This is possible because the slug feeds on hydroids which contain symbiotic zooxanthellae, microscopic dinoflagellates that are photosynthetic — in other words that have the capability to make sugars from sunshine. The nudibranch farms these zooxanthellae within its own digestive diverticula. The zooxanthellae then convert the sun's energy into sugars. The sugars are used by the slug.
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