Underwater Pages

Home
Reef Animals
UW Photo How-to
Scuba Diving

Reef Animals

Up
Nudibranchs
Coral Reef
Venomous Animals
Angelfish
Butterflyfish
Damselfish
Puffers
Sharks & Rays
Snappers & Breams
Surgeon/Rabbit Fish
Triggerfish
Wrasse & Parrotfish
Other Reef Fish

Nudibranchs

Picasso Critters on the Reef

The naked gills of a nudibranch look like feathers
The naked gills of a nudibranch look like feathers

Nudibranchs, or nudis as they are affectionately called, are some of our favorite sea critters: colorful, bizarre, and endlessly challenging to find.  Their small size (often less than 1 inch!) makes them a real challenge for our age-hindered eyes!

In layman terms, "nudibranch" is sort of a catch-all name for a whole group of generally small, colorful sea critters that are often oblong or cylindrical and maybe only an inch or 2 long (though the flamboyant Spanish Dancer nudibranch can attain 18 inches!). Many people lump almost any soft-bodied, colorful critter into the "nudibranch" category.

Nudibranchs, aka Sea Slugs, belong to the Phylum Mollusca, a huge Phyllum of animals that includes all the sea shells and bivalves like clams, cephalopods like squid and octopus. There are literally tens of thousands of species of Mollusks in the world, and most live in the ocean.

More specifically, nudibranchs are part of the Class Gastropoda, Subclass Opistobranchia. Sea slugs generally have soft bodies (no external shells) and their mantles are brilliantly colored and cover their backs.  Nudibranch literally means "naked gills" and most of these creatures have feathery masses on their bodies that are their naked, external gills. They are of many shapes and colors, but most all have two rhinophores, or thick sensory tentacles near the head. Some nudibranchs have hidden gills on the sides and some have a mass of "hairy looking" cerata on their backs which are actually part of their respiratory system.

We only started finding nudibranchs in 2015 while diving with Triton Bay Divers in Papua, Indonesia.  The dive guides there are great at locating these beautiful little critters, and now we're getting better at it ourselves.  Unfortunately as we get older and our eyes get worse it gets harder and harder and to see them.  The key is to look for bright contrasting colors of an oval or oblong shape.  You pretty much have to ignore all the busy fish moving around to do this!  Luckily, most nudibranchs move very slowly so they are not hard to photograph if you have a light and the right lens.  That being siad, we have encountered nudis that can move their full body length in a minute or less, creeping around the edge of a bommie going out of sight.  Many nudibranchs hang out under overhangs and in crevices, so you have to look closely, or turn upside down maybe to find them.

A note on identification:  Of the hundreds of nudibranchs that have been "found" and photographed, a relatively small number have actually been scientifically "described".  For an animal to be described it has to be captured and studied and dissected and have its DNA analyzed.  Given that Genus is often determined by physiological likeness to other creatures in that genus, scientists can often give a pretty good guess as to the genus of an undescribed nudibranch, but until more studies are done, this is only a temporary classification.  New species are being discovered every year and more and more species are getting themselves an official scientific name every year.  But there are so many creatures in the sea that we still don't know about.  That's one thing that makes this amateur "animal hunt" so exciting.

Here are a few of the amazing nudibranchs we have discovered while diving and snorkeling.  Don't forget to click on a picture to see a bigger version!

Unless otherwise noted, all specimens were photographed in eastern Indonesia, in either Raja Ampat or Triton Bay, areas renowned for their multitude of small sea critters.

 

The simple, but beautiful Funeral Jorunna
The simple, but beautiful Funeral Jorunna
The spotted hypselodoris is an elegant nudibranch
The spotted hypselodoris is an elegant nudibranch

At left, the Spotted Hypselodoris H. maculosa, ispart of a large genus of nudibranchs, all with elongate bodies and many with a combination of stripes and spots. On this speiceis the rhoniphores are banded with brown-red and white.

 

At right, the beautiful white and black nudibranch is in the Genus Jorunna, in which there are at present only a few named species.  This one is the Funeral Jorunna, J. funebris and is characterized by the black circular markings which appear fuzzy due to fine, erect papillae.

A pair of chromodoris nudibranchs, unsure ID. Maybe Coi
A pair of Chromodoris nudibranchs, unsure ID
Two examples of nudibranchs from the well populated Genus Chromodoris. Animals in this genus are dorid nudibranchs, meaning they have the characteristic external anal gills and  rhinophores near the head. They come in a wide variety of colors and patterns.  The 2 animals at left may be Chromodoris coi, but we're not sure, as the colors and pattern don't match our reference books clearly. Nudibranchs often "tailgate" one another, with the second one following the slime trail of the first as they move across the reef looking for food.

At right is the slightly warty Geometric Chromodoris with white tubercles surrounding a lavender dorsum (back).The white rhinophores with green tips are characteristic. This was found deep under a ledge and we had to practically stand on our heads while scuba diving to photograph it.  That our friend Dave saw it to begin with was amazing!

 
A lovely pastel Chromodoris geometrica under a ledge.
A lovely pastel Chromodoris geometrica under a ledge.
A stunning snudibranchl that we haven't ID'd. By Rainer
A stunning Tyron's Risbecia nudibranch.  By Rainer
The nudibranch on the left is a Tryon's Risbecia R. tryoni. It can attanit 2.75 inches so is easily spotted if you're nearby. Rainer got the best shot of this beauty in Triton Bay. (Triton Bay. Photo by Rainer)

At right is a Blue Dragon Pteraeolidia ianthina whcih can be a variety of colors from this dark blue to a pale blue, yellow green or tan. The swirly things on its back are cerata.  All Blue Dragons have blue or violet bands on their rhinophores and oral tentacles. THese can be up to 4 inches long and we have seen them several times.

 
The Blue Dragon is one amazing critter!
The Blue Dragon is one amazing critter!
A Swollen Phyllidia with tiny red crabs on its back
A Swollen Phyllidia with tiny red crabs on its back

The Genera Phyllidia and Phyllidiella together account for dozens of species, each with very noticeable "warty" appearance.  To tell one species from another it's necessary to study the pattern of lines and "islands" of color or tubercles to see the differences.  These are all pretty common on the tropical Pacific reefs.

On the left is a P. varicosa, or, in common terms a Swollen Phyllidia.  In the enlarged photos (click on the small one) you can see small red crabs, maybe on the dorsum, something that we didn't see until after the photo was taken!

At right are a pair of P. pustulosa ("postulosa" meaning bumpy, which could apply to most any of this genus!)  The English common name is Pimpled Phyllidiella.

A pair of Pimpled Phyllidiella communing on the reef
A pair of Pimpled Phyllidiella communing on the reef

 

A Swollen Phyllidia with tiny red crabs on its back
A Swollen Phyllidia with tiny red crabs on its back
At left is another species in the stable of Phyllidia nudibranchs, is the Sky Blue Phyllidia, characterized by 2 black stripes and a broekn central jstripe. Both the rhinophores and tubercle tops are yellow-gold.  They are known to feed on sponges. Latin name: Phyllidia coelestis.

At right is a hunched up picture of a Shreens Phyllidiopsis, a close relative of the Phyllidia and Phullidiella genera.  The pink rhinophores of this Shreens are not visible in the picture.

A Shreens Phillidiopsis hunched up on the reef.
A Shreens Phillidiopsis hunched up on the reef.

Ocellated Phyllidia with orange & black patterns
Ocelot has our own nudibranch!  Well, at least by name. At left is the compelling orange, black and white Ocellated Phyllidia P. ocellata, which we just encountered in Triton Bay in mid-2017.  It is big enough that we could spot it with our own eyes, being almost 3 inches long! (Triton Bay. Photo by Jon Hacking)

 


 

At right we're out of the Phyllydia genus and their cousins. This beauty  is probably in the Chromodoris Genus, as it has many similar looking critters in our book.  But the closest, the C. Anna's describes the animal as NOT having a complete central stripe and the blue mantle having black speckles, which this specimen does not.

(Misool, Raja Ampat Photo by Sue Hacking)

 

.
Chromodoris sp. nudibranch. No larger image.
The Dark Fringed Glossodoris is bright on the reef.
The Dark Fringed Glossodoris is bright on the reef.
At left is a frilly, white and black Glossodoris atromarginata, or Dark Fringed Glossodoris nudibranch.  This iis one of the larger nudibranchs, having been recorded up to 4in long. That means we can see it better, too!

At right Mushroom Coral Reticulada, Reticulada fungia is strange with its very clear ridges that give it a stiff, rather than soft-looking back. Size, about 1.5 inches.

The Mushroom Coral Reticulata has sharp ridges
The Mushroom Coral Reticulata has sharp ridges

Up | Nudibranchs | Coral Reef | Venomous Animals | Angelfish | Butterflyfish | Damselfish | Puffers | Sharks & Rays | Snappers & Breams | Surgeon/Rabbit Fish | Triggerfish | Wrasse & Parrotfish | Other Reef Fish

Reef Animals | UW Photo How-to | Scuba Diving

Top Level: Home | Destinations | Cruising Info | Underwater | Boat Guests | Ocelot | Sue | Jon | Amanda | Chris | Site Map | Make a Comment


The Triton - Nautical News for Captains and Crews
If our information is useful,
you can help by making a donation

Copyright  2000‑2017  Contact: Jon and Sue Hacking -- HackingFamily.com, svOcelot.comAll rights reserved.