The curiosities of the Blue dragon nudibranch
Commonly referred to as the Blue dragon nudibranch, Pteraeolidia ianthina (Nudibranchia - Facelinidae), is a remarkable species of sea slug native to the Indo-Pacific region.
This is an extremely elongate species up to 5cm long, with large, curved arches of cerata (the projections on the upper surfaces of the body) along the length of the body. The cephalic tentacles have two distinctive dark purple (or blue) bands.
Although the body color of this nudibranch is translucent tan, the cerata, which are mostly blue or dark purple, lavender or golden brown, give the nudibranch most of its apparent color.
The Blue dragon nudibranch has many amazing survival strategies. When touched, the nudibranch will “flare” its cerata and the nematocysts will discharge on contact (it is one of the few nudibranchs with a sting strong enough to be felt by humans though usually not in areas with thicker skin such as the palm of the hand).
It is also able to autotomize (lose or detach) the posterior part of its body in order to distract, or free itself from, a potential predator. Later, the missing portion can be regenerated.
Another curiosity of this species is that the cerata contain zooxanthellae of the genus Symbiodinium that exhibit the capacity for photosynthesis, and they grow while reside in the sea slug. This symbiotic relationship with the algae helps the adult nudibranch to overcome a period of food shortage by getting photosynthetic products.
Photo credit: ©Sylke Rohrlach
Locality: New South Wales, Australia