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.

References: [1] - [2] - [3] - [4]

Photo credit: ©Sylke Rohrlach

Locality: New South Wales, Australia

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Hermissenda crassicornis

Sometimes known as the “opalescent sea slug”, H. crassicornis is a species of Facelinid nuibranch which inhabits coastal intertidal zones from Alaska south to Mexico. Like other nudibranch species H. crassicornis feeds mainly on sessile invertebrates, specifically hydrioids and occasionally sea anemones, tunicates, and others. 


Animalia-Mollusca-Gastropoda-Heterobranchia-Euthyneura-Nudipleura-Nudibranchia-Dexiarchia-Cladobranchia-Aeolidida-Aeolidioidea-Facelinidae-Hermissenda- H. crassicornis

Images: Brocken Inaglory and Jmalin


Nudibranch part [2]

Parts [1] [3] [4]

1 - 2: Elysia crispata (not a true nudibranch)

3: Hexabranchus sanguineus

4: Hexabranchus sanguineus egg ribbon

5: Hermissenda crassicornis

6 - 7: Hypselodoris apolegma with egg ribbon

8 -10: Hypselodoris bennetti

Photography by:

1 - Ann Dornfeld 

2 - Anthony Holley 

3 - Pilgrim143 

4 - Niall Corbet 

5 - Ashley Hauck 

6 -  Ken Tucker 

7 - Pippadoodle 

8 - Alastair Pollock 

9 - Doug Anderson 

10 - James van den Broek 

Sea Slug - Phyllodesmium serratum 

Phyllodesmium serratum (Nudibranchia - Facelinidae) is a colorful species of sea slug known from Japan, Philippines and Australia, whose color is dependent on the color of the food it is eating.

As seen in the photo, it has branched digestive glands that ramify into the cerata and dorsal surface of the body.

Although one of the most interesting adaptations found in this genus is the widespread participation in a symbiotic relationship with photosynthetic dinoflagellates (zooxanthellae), P. serratum does not have such a relationship, and is unusual in feeding on a wide variety of octocorals.

References: [1] - [2] - [3]

Photo credit: ©Klaus Stiefel (CC BY-NC 2.0) | Locality: Kurnell, Sydney, New South Wales, Australia (2013)

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Phyllodesmium briareum

…is a species of Favorinine nudibranchi (Facelinidae, Favorininiae) which is widely distributed throughout the Indo-Pacific and Australia. Phyllodesmium briareum are noted to feed mainly on various corals, specifically members of the suborder Sleraxonia. P. briareum is also noted for its ingenious camouflage, its cerata (the gills along its back) have been modified to look almost exactly like the tentacles of the Sleraxonian coral Briareum violaceum (which you can seen in the second picture above) this allows P. briareum to feed among B. violaceum without being targeted for predation!


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Images: Steve Childs and Heike Wägele & Annette Klussmann-Kolb

Orange Godiva - Dondice banyulensis 

Compared to other nudibranchs, the sea slug Dondice banyulensis (Nudibranchia - Facelinidae) is great, as can measure up to 7 cm in length. Moreover, it is easily recognizable by its distinctive orange color and the presence of three longitudinal white lines going through the dorsum, as well as a white band on the margin of the foot.

This species lives on rocky bottom in the Mediterranean Sea and nearby Atlantic coastal waters.

References: [1] - [2] - [3]

Photo credit: ©Antoni López-Arenas | Locality: La Depuradora, L'Escala, Catalonia, Spain, 15m deep (2010)

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Phyllodesmium magnum in the night | ©Berthomier Jack

As its scientific name suggests, Phyllodesmium magnum (Nudibranchia - Facelinidae) is one of the larger species in the genus. From the branched arrangement of the digestive gland, flattened cerata, and position of zooxanthellae in the sunlit parts of the skin, it is most probably one of the species which retains zooxanthellae alive in its tissue so that it can benefit from their photosynthetic activity.

This species is known from tropical Western Pacific, and Western Australia [1].

Growing up to 130 mm length, this sea slug is characterized by its flattened, curved brownish cerata which have often a bluish tinge and yellowish apices. It rapidly drops off many of its cerata when disturbed (autotomise) [2]. 

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Pteraeolidia ianthina

…a strikingly marked species of of Facelinid nudibranch which is known to occur among shallow coral reefs throughout the Western Pacific Ocean, from Hawaii to the Philippines, to the waters of northeast Australia and parts of New Zealand. It is also known from the Red Sea. P. iathina is known to feed almost exclusively on hydroids, generally those which contain Symbiodinium spp. These dinoflagellates are “farmed” in the digestive diverticula of P. iathina allowing the sugars they photosynthesize to be used. 


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Image: Richard Ling

Hermissenda crassicornis - Opalescent Nudibranch | ©Marlin Harms   (Cayucos, California, US)

Hermissenda crassicornis (Nudibranchia - Facelinidae), better known as the Oplescent Nudibranch, is among the most beautiful sea slugs.

Its length is about 8.3 cm and has distinctive colors bluish-white with an orange line down the middle of its back. The margins have pale electric blue lines. These colors are mainly carotenoids and carotenoproteins.

It has two pair of tentacles (rhinophores) located on the top of the head. The first pair has blue lines, and the second pair is bluish with raised rings. In the middle, there are numerous finger-like projections, called cerata, in two clusters on each side of the back. These projections are brilliantly colored in bright orange with a white tip on each ceratum. The coloration of the H. crassicornis serves as a great identification factor for the species.

Hermissenda crassicornis are commonly found in areas of the West Coast of North America from Kodiak Island, Alaska to Baja California, Mexico.


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