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Trip Report - Nudibranch Convention
Report from Wakatobi Dive Centre
With the creation of Nudibranchs, Mother Nature expressed her wildest indulgence of colors and forms. This month
in Wakatobi, as the water temperature drops to 27 degrees, there seems to be a simultaneous increase in the size,
variety and amount of Nudibranchs. The dive team decided to focus on these amazingly beautiful "butterflies of the sea".
Hypselodoris bullock - Tom Fretz
Nudibranchs belong to the Phylum Molusca, along with other sea shells or molluscs. They are part of the class of
the gastropods, or univalves and belong to the sub-class Opisthobranchia, along with sea hares and slugs. These
colourful and bizarre creatures have astonishingly remarkable and diverse lifestyles, features and shapes.
Noumea Crocea - Richard Smith
There are more than 3000 describes species of nudibranch, with new ones being identified almost everyday! Their size
ranges from just a few millimeters to around 300 mm. They can be found in all the oceans of the world and within
most habitats, but are more abundant in shallow, tropical waters.
The scientific name "nudibranch" comes from the Latin nudus, naked, and the Greek brankhia, gills - "naked gills",
which is quite appropriate as many nudibranchs have dorsal gills at the rear, shaped like bushy plumes, from which
they breathe - 'naked gills'.
Spanish Dancer - Burt Jones and Maurine Shimlock
Almost all of the Opisthobranchs are very interesting critters, fully functional hermaphrodites, born with male and
female sex organs, thus have a set of reproductive organs for both sexes.
Chromodoris willani - Miguel Ribeiro
Most mature nudibranchs have reproductive genital openings on the right-hand sides of their upper bodies close to the
"neck". Once members of the same species have recognised each other by smelling each other and tactile body contact,
there is often some courting. They manoeuvre around in opposite circles to get their reproductive pores aligned. One
might follow the other around touching on the edge of its tail for some time before the one in front gets the message.
The well-documented behaviour of 'tailing' can be a prelude to mating, as well as a lead to food behaviour.
Chromodoris Dianae - Eric Cheng
Mating itself happens when a nudibranch pair reach a 'head to tail' position, with their 'necks' touching,
lining up their genital papillae. On contact, each penis everts from the neck and seeks out the female genital
duct to pump in sperm. This can last from minutes to days!
Chromodoris annae - Eric Cheng
Some species of Opisthobranch may form communal mating, or spawning groups, while others just pair up after some
'courting', copulate, then move on to lay their respective egg ribbons. The egg ribbons can come in an amazing
array of size, shape, colour and design, depending on species and are usually laid on, or near food sources.
Nudibranch eggs - Frank Owens
The majority of parents then abandon the eggs and move on. Most egg masses are toxic, to deflect predators.
The next stage of development is again dependent on species - direct development where the young emerge, crawling
out of their egg, or planktonic larval dispersal, drift around in the currents until they settle and metamorphose
Nembrotha lineolata - Paul Sutherland
Opisthobranchs are as diverse in their food preferences and habits as they are in shape, pattern and colour.
Some are voracious cannibals, feeding on other Opisthobranchs, while others slowly ply their way forwards,
grazing on, but not limited to algae, sponges, anemones, corals, barnacles, fish eggs and crustaceans.
Nembrotha Kubaryana - Richard Smith
They have two highly sensitive tentacles, called rhinophores, located on top of their heads, which allow them
detect odours in the water currents. They often use touch and tactile senses to detect the presence of prey.
Colouring and Defense
Flatworm - Frank Owens
Opisthobranchs include some of the most colorful creatures on earth. They use a variety of weapons to aid in
protection, from chemical and biological to swimming escape responses, warning (asposomatic) colouration and
Sea slugs, similarly to land snails, can leave a trail of slime behind, which provides a great deal of information
to other nudibranchs. An attacked sea slug can release chemicals into its slime trail to warn other slugs, it can
follow a slime scent to find a mate.
Chromodoris Koi - Eric Cheng
Some Opisthobranchs evolved with textures and colors that mimick surrounding plants to avoid predators. Others,
as seen especially well on the nudibranchs chromodorids, have an intensely bright and contrasting color pattern
that makes them especially conspicuous in their surroundings. This is believed to be an example of aposematic
coloration; the shockingly bright coloration which warns potential predators that their prey-to-be is distasteful
Some even retain the foul-tasting poisons of their prey and secrete them as a defense against predators. After
the first unpleasant encounter with a noxious nudibranch, the predator learns its lesson and subsequently avoid
that badly tasting animal.
Flabellina exoptata - Saskia Van Wijk
Nudibranchs that feed on hydroids can actually store the hydroids' stinging nematocyst cells in their body
without harming themselves. The Flabelinas digest the hydroids and can then concentrate the specialized
projectile-emitting cells for future discharge at the end of their tips, a fantastic defense against potential
Chromodoris magnifica - Steve Miller
This well known Chromodoris magnifica has a shell only during its larval life. It depends on classic aposematic
coloration to warn predators that it is toxic or extremely distasteful.
Phyllidia varicosa - Steve Miller
The sponge-eating phyllidia varicosa is very common on Wakatobi's reefs and is part of a group of nudibranchs
with a repellent chemical defense, that fishes and crustaceans then associate with its blazing colors and learn
One taste of the lovely Hypselodoris bullocki (1st photo) is usually sufficient to teach a predator that it is a bitter
mouthful. Scientists believe that the natural toxins produced by reef invertebrates such as this may have
future commercial or medicinal applications.
Swimming flatworm - Troy Cheek
One of the highlights of the last dives was a free swimming Bedford's flatworm. Some of our lucky guests managed
to not only observe, but actually take pictures while this colorful flatworm swam along.
Flatworm Pseudoceros bifurcus - Saskia Van Wijk
Flatworms are similar to Nudibranchs in many ways, although unlike most Nudis Flatworms have no external gills.
Some have marginal tentacles at one end which may contain simple eyes, and other species may have dorsal
tentacles issuing from the back near the "head".
Chromodoris annae - Frank Owens
Wakatobi Reef Vista - Steve Miller
On Wakatobi's reefs, there is a very wide variety of Nudibranchs and Flatworms right now, although the majority
of them are present year round. They thrive on healthy reefs and this is yet another sign of just how pristine
Wakatobi's protected reefs are.
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