Dear Franco,

I first encountered this little animal when I was revising the Indo-West Pacific species of Hypselodoris and Chromodoris and was pretty sure it was a Chromodoris  and had placed it with a group of similarly coloured species [see C. decora colour group Fact Sheet] which I was planning to dissect as a group. Howevere I was greatly surprised when I dissected it to find its radular teeth were quite different from a chromodorids and its anatomy showed it was a juvenile Hexabranchus sanguineus.

If you look through some of the messages we have of this species on the Forum you will see stages showing its chnage form this colour pattern to the brilliant red and white of the adult Spanish Dancer.

Best wishes,
Bill Rudman

Dear Dae,

Nice to get an easy one now and again. Although it looks a bit sad washed up, this is the spectacular Hexabranchus sanguineus commonly known as the Spanish Dancer, because as it swims by flapping its wide colourful mantle skirt, it is reminiscence of a flamenco dancer.

In the close-up alongside which shows the circlet of gills you will see there are six which is why it was named Hexabranchus [hexa = six; branchus = gill]. The name sanguineus [= bloody] is not a reference to the great Australian adjective but to the red splashes all over the mantle skirt. Have a look at the two pages of messages on this species [Page 1, Page 2] for more information.

Best wishes,
Bill Rudman

Thanks Gary,

At this size they certainly look like a different species.

Best wishes,
Bill Rudman

Dear Sully,

This colourful little animal immediately makes you think that you have found a nice chromodorid, but it is in fact a juvenile Hexabranchus sanguineus. There is no easy way to distinguish it externally as a Hexabranchus at this small size because the characteristic oral lobes and separate gills are not clear at this early stage of its growth. When I was reviewing chromodorids with this colour pattern I thought I had a new species until I had a look at its anatomy and realised my mistake.

Best wishes,
Bill Rudman

Dear Chris,

This is Hexabranchus sanguineus. It is often found swimming and the ways it swirls it mantle skirt when swimming has given it the common name of the Spanish Dancer. Have a look at the Fact Sheet [and page 2] and the messages attached to those pages for more information

Best wishes,
Bill Rudman

Dear David,

I haven't felt the need yet to say 'no more' for any species.

I am surprised at how few photos we have on the Forum of Periclimenes on Hexabranchus but if you do a search for Periclimenes on the Forum you will find lots of photos of it associated with other opisthobranchs. I am pretty sure the shrimp on the gills is a juvenile of Periclimenes imperator. The white-spotted colour form of your larger animal is not the usual colour form of this species which usually has a white band down the back and a wider white collar just behind the 'head' [see photo on Symbiosis Fact Sheet]. The white spots are usually present on the posterior end of the body. If you look carefully at the gill-dwelling animal you can see a faint whitish collar behind the head.

Faecal pellets can be a useful indicator of food specificity, and  from the orange bits I can see in your photo I suspect it has been eating an orange sponge. JUst knowing the colour of its food is not enough but if you found an animal producing faecal pellets with orange bits and it was sitting on an orange sponge, or surrounded by an orange sponge it would be a valuable clue. In sponges that have siliceous spicules, finding large numbers of thsoe spicules in the faecal pellets is also a valuable clue, but sponge spicules are scattered all over the sea bottom, so finding an identifying a few sponge spicules from an slug's stomach may be misleading and just indicate that they don't wash their food before eating it.

Best wishes,
Bill Rudman

Dear Ed,

Its definitely Hexabranchus sanguineus. It seems in some places this species has a reputation for growing rather large. I comment on the large ones [about 2 feet long] from Djibouti in an earlier message which reports large animals from Fiji [#2965] - another place where 'giants' have been found quite often.

Best wishes,
Bill Rudman

Dear Natasja,

Yes it certainly seems to be feeding on a reddish sponge. Hexabranchus is reported to feed on quite a few different species of sponges [see references page], but we still have much to learn of its biology and natural history

Best wishes,
Bill Rudman

Thanks Diane,
The message you are referring to was posted in 2000 - I hope Marco found a video before now.

Best wishes,
Bill Rudman

Dear Natasja,

I am not sure if there is an abnormality or not. Hexabranchus is unusual in that every gill is attached separately to the body wall, not into a common trunk or vessel as occurs in most dorids. The name Hexabranchus comes from the Greek words for six gills and it is usual to have six, sometimes seven, separate gills arranged in a circle around the anus. In this animal a couple of the gills seem to be missing and I can't see the anus. It could be some developental abnormality or damage that has repaired itself - I can't say.

I have included a close-up of the head region because its shows another peculiarity of Hexabranchus - the strange hand-like [palmate ] lobes on either side of the mouth which replace the normal oral tentacles. These lobes have a series of fingerlike papillae around the edge which no doubt have a sensory function. There is considerable debate about the significance of these lobes, and the gill structure, in understanding just which dorids Hexabranchus is most related to.
Best wishes,
Bill Rudman

Thanks Natasja,
These orange-red animals certainly show how appropriate the scientific name is [ sanguineus = bloody] - mind you, that's excluding the Australian use of the word of course.

Best wishes,
Bill Rudman

Dear Don,
If you are looking for something on the Forum like a scientific name its always worth using the Forum search box on top left of every page. I dont encourage common names but the Spanish Dancer is one that is definitely in common use. It scientific name is Hexabranchus sanguineus [hexa = six; branchus = gills; sanguineus = blood red].

I am glad you didn't find the scientific name yourself because I migth never have found out you had found this species in Sydney. I know I often tell people you have to expect to find tropical species in Sydney every now and then but I must say this is the first time I have heard of this icon of tropical waters being found this far down the New South Wales coast.

For thos of you who don't know Long Reef, it is a rocky reef jutting out at right angles from the shore like an arm outstretched to catch larvae washing past. I remember seeing a list of the tropical cowries in the Australian Museum collections from Long Reef, and if you didn't know where it was you would have been sure, from the number of species on the list, that Long Reef must be in the middle of the Great Barrier Reef, rather than the temperate waters of central New South Wales. But the list was an accumulation of finds over 100 years not from a day or a week. Be that as it may, I still find it amazing that Sydney has played host to a Spanish Dancer for sufficient time for it to grow to 200 mm.

Best wishes,
Bill Rudman

Thanks Jen,
I've added his name to the original message.
Bill Rudman

Dear Jen,
Can you please let me know the name of the photographer so I can add it to the message please.

This is a form of Hexabranchus sanguineus. Have a look at the Fact Sheet and associated messages for further information. From the size of the hand in the photo this is obviously one of the 'giants' which are sometimes reported from various parts of the Indian and Pacific oceans.

Best wishes,
Bill Rudman

Thanks Asther,
One interesting feature of Hexabranchus is that instead of having a single oral tentacles on either side of the mouth it has a flattened hand-like lobe. In your photo you can see the 'fingers' of the left lobe poking out from under the mantle skirt

Best wishes,
Bill Rudman

Dear Sandrine,
I know of no evidence that it feeds on either the anthozoan coral, Millepora, or brittlestars like Ophiocoma. Certainly Ophiocoma lives entangled in branching corals and coral rubble and is usually only seen in numbers like this when it crawls up to the water surface as the tide turns, to collect the dried organic particles and 'scum'  it eats from the water surface. Hexabranchus is often found in coral rubble and areas of small branching coral colonies. Like many dorids, it is able to nestle into very small and inconvenient cracks and crevices when it is not actively crawling or feeding.

I suspect there is nothing significant about finding these three animals together.

Best wishes,
Bill Rudman

Dear Roxanne,

This animal is a juvenile, or at least subadult, Hexabranchus sanguineus. When they are small they are often mistaken for a species of Chromodoris. It's a bit hard to see but one way small Hexabranchus can be identified is the way the gills are each attached individually to the mantle, and there is no real gill pocket into which they can retract.

I have moved one of the species you mention into a separate message. Can you please remember to include only one species in a message - unless of course it is a message about multiple species.

Best wishes,
Bill Rudman

Dear Kamal,
Although you are correct in observing that swimming in Hexabranchus is often initiated by humans, that is not always the case. I have certainly found swimming animals in deserted places where there are no signs of other people around, and I have also seem animals crawling along and spontaneously beginning to swim. The behaviour of quickly opening their folded over mantle to show their brilliant red and white colours, and their swimming, is considered to be a defence mechanism.

Best wishes,
Bill Rudman

Thanks Joe,
This bright red variety seems to be quite common in the Red Sea. It is indeed a spectacular sight when it is swimming

Best wishes,
Bill Rudman

Dear Kevin,
Thanks for these photos. Spanish Dancer is one of the few 'common names' which are truly common names in the sense of being commonly used world-wide - at least by English speakers. Yoir photo alongside of a swimming animal shows just how appropriate this name is.

The yellow animal shows the strange hand-like oral tentacles found in this species, and I am pretty sure I can see a commensal shrimp on the right side of the animal just behind the right rhinophore [left side in photo]. The other close-up shows a much enlarged view of one of these shrimps - Periclimenes imperator - which are found living on a variety of large sea slugs

Best wishes,
Bill Rudman

Dear Molly,
The purpose of the Forum is to build up a store of information on sea slugs by keeping the contributions people make so it is available for future use. This means that the Fact Sheets are only a starting point for information. For example, if  you want to know about the Spanish Dancer you don't just look at the Fact Sheet, you also look through the messages that have accumulated on that species. If you are lucky, someone will have already asked the question you are interested in, and received a useful answer. People's views on a topic, and identifications, may change over time, so the Forum is also an historical record of changing views and ideas. 

More importantly, a lot of time has been spent by me and others providing observations and answers. These answers were not just for the person who asked the question, but for anyone who would like to know.  If I remove them, I might as well have sent you a private email, which negates the whole value of the world wide web to share and disseminate information. Your 3 year old message is still on the Forum, not because I haven't got around to getting rid of 'out of date' messages, but because I don't plan to delete them. The Forum is not part of our 'throw away society' - all messages on the Forum are valuable, no matter how old they are.

Best wishes,
Bill Rudman

Dear Brian,
Yes this is indeed a juvenile Hexabranchus. Good call! The gills in juveniles are quite interesting. The dorid nudibranchs are divided into two large groups depending on whether their gills can retract into a protective pocket [Cryptobranchia or Eudoridoidea] or do not have such a pocket  [Phanerobranchia or Anadoridoidea]. Obviously in adults, Hexabranchus has no sign of a gill pocket and each gill is separately inserted into the skin. It would seem to be clearly a phanerobranch. However phanerobranchs are usually the elongate forms, such as the nembrothids,  while the large flat dorids with wide mantle skirts are usually cryptobranchs, with a gill pocket. Cryptobranchs are also sponge feeders, like Hexabranchus, while the phanerobranchs are all specialised feeders on a wide variety of invertebrates. There are of course other anatomical differences.

However if you look at juvenile Hexabranchus, you can see there seems to be a ridge around the gills and the tissue inside that is translucent, without the colour pattern of the rest of the mantle. I wouldn't be surprised if that is all that is left of a gill pocket, which has been lost in the evolution.of this species, but is still indicated in juveniles. Does that make Hexabranchus a very special cryptobranch, or does it suggests that it is a link between the two groups, indicating that the phanerobranchs evolved from the cryptobranchs? I wouldn't like to say.at this stage, but it is certainly something that students of phylogeny should consider. I'm glad you picture shows it so clearly. In living animals they gills can almost completely disappear.
Best wishes,
Bill Rudman

Dear Joe,
Sorry to be a spoilsport, but as far as I know, 'kissing' has never been considered a behaviour that sea slugs engage in. Not being able to see, one of the main ways slugs can make sense of their surroundings is through touch. Often when two animals meet head to head like this they will nudge around, no doubt searching for the right 'smells' on the other animal. If all is well, they then have to respond by moving down the right side of their partner's body so that their mating organs are aligned.
Best wishes,
Bill Rudman

Thanks Joe,
Since 'Hexabranchus' means 'six gills', perhaps we should call this Monobranchus. I can't say whether this is a development problem or predator damage. I'll add it to the abnormalities page.

An earlier message from Erwin Koehler [#2964 ] of an animal from the Gulf of Aqaba, with 4 gills, suggests that something may have a liking for these gills. In both animals there seems to be a 'stump' where each gill should be.
Best wishes,
Bill Rudman

Dear Reindert & Mieke,
It is interesting to see this plain orange colour form which I also found in Tanzania, just north of Madagascar. It is hard to be sure if there are two tubes there, but if there are it's what you would expect, as these animals are hermaphrodite, each animal having a fully functional male and female reproductive systems. Sometimes they mate as either a male or a female, but usually mating is reciprocal, so sperm is exchanged during matings by both partners. If there are two tubes here, they will be part of the male reproductive apparatus, each partner inserting its penis into the vaginal opening of the other.
Best wishes,
Bill Rudman

Thanks Colin,
These are quite interesting as they show a gradation from your previous juveniles to more obvious Hexabranchus. You can see reddish spots and blusih white bands of the juveniles but the folded mantle edge and submarginal reddish orange band of the adults.
Best wishes,
Bill Rudman

Dear Colin,
I wish it was H. rudmani - I haven't seen many photos of my namesake. However these are juvenile Hexabranchus sanguineus, an animal that fools the best of us. When I was doing a review of all the little red and purple spotted chromodorids I was sure this was a chromodorid until I looked at its anatomy. The only external clue are the gills don't have a real pocket to retreat into. See Robert Sozzani's photo [#9954].
Best wishes,
Bill Rudman

Dear Marco,
You were right when you gave the photo the file name 'ballerina_spagnola'. It is indeed the Spanish Dancer, or Hexabranchus sanguineus. As we can see in your photo, when the animal is crawling or 'resting' the edges of the mantle fold over and hide the bright red and white colour pattern. However when it is startled or disturbed, the mantle rolls open to display the bright colour pattern, and swimming is sometimes initiated. We think this is a 'startle display' to frighten predators. See the Fact Sheet on colour patterns for more information.
Best wishes,
Bill Rudman

Dear Kamal,
I am not saying that you are mistaken. Your egg  ribbon is probably that of Hexabranchus, but it is possible that another big dorid nudibranch may have laid the egg ribbon. I need to be sure that the 'facts' on the Forum are backed by evidence. Egg ribbons are a good example. An animal may lay an egg ribbon then crawl away. The another animal of a completely different species may crawl up to it just as a photographer swims by. If we assume that the closest animal to an egg ribbon is the 'mother' we will make many mistakes. That's why I asked.

You are probably right in assuming that it is the egg ribbon of Hexabranchus, but that is not the same as actually witnessing it being deposited. For the Forum to be a source of reliable information for you - and all other readers - I need to feel confident that any statement about an animal's biology or anatomy on the Forum is supported by first-hand evidence. I am happy for 'probable sightings' to be included, as long as we all know that we are not absolutely sure.
Best wishes,
Bill Rudman

Dear Kamal,
Thanks for these photos. This uniformly red colour pattern is the one illustrated by Ruppell & Leuckart (1828) in their original description of this species from The Red Sea. Your photos also show one of the characteristic features of Hexabranchus which is that each of the gills is attached to the body wall by an independent stalk. The name suggests their should be 6 gills [Hexa = six; branchus = gills] but sometimes, as in your animal, one of the main stalks may branch so it appears there are 7 gills, or even 8.

Can you confirm the egg ribbon is that of Hexabranchus? It certainly looks like it, but it would be valuable to know why you think so.
Best wishes,
Bill Rudman

Dear Nils,
If it layed this egg ribbon then clearly its not a juvenile Hexabranchus. I am not sure if you are collecting as well as photographing. If you have the specimen then there are 2 things to look for in the specimen which would give you a good idea whether it is Hexabranchus or not. In Hexabranchus the gills insert into the skin separately while in most other dorids they join together at the base into a single 'trunk'. In juvenile preserved animals the separate gills are not easy to see if there is some shrinkage, but it's worth having a look. The second thing to look for is the shape of the oral tentacles on either side of the mouth. In adult Hexabranchus there is a unique hand-like flap on each side of the mouth with a series of finger-like papillae around the edge. Again in juveniles this is only partly developed and my not be visible in a preserved animal but again worth looking for. If it is not a Hexabranchus then there are a number of cheomodorids which it could be. Have a look at the Chromodoris decora colour-group Page for a list of possibilities
Best wishes,
Bill Rudman

Dear Nils,
I think this little animal was specially designed to fool nudibranch workers. Despite appearances it is a juvenile Hexabranchus. You can see how the edge of the mantle is already beginning to fold over.
Best wishes
Bill Rudman

Thanks Erwin
Bill Rudman

Dear Gary,
Congratulations on discovering its secret. The apparently separate gills is one of the main characters for this genus, and its name Hexabranchus means 'six gills' a reference to the separate gills, the number of which can vary a bit. Have a look at Robert Sozzani's message where I discuss the gills in a photo he has of a juvenile animal
Best wishes
Bill Rudman

Dear Roberto,
This little animal often tricks even the experts into thinking its a chromodorid but it is a juvenile Hexabranchus sanguineus. If you look carefully at your photo you will see that each gill is separately attached to the body, rather than being joined basally. This is characteristic of Hexabranchus.
Best wishes,
Bill Rudman

Thanks Mary Jane,
Yes the oral tentacles in Hexabranchus have this hand-like appearance, similar to the way the oral veil in Bornella has divided into a pair of 'fingered' [digitate] lobes.
Best wishes,
Bill Rudman

Dear Molly,
There is all the information you are likely to need on the Forum - and there are references to even more information which you probably won't need. But since it is your research paper I'll tell you where it is on the Forum so you can have the satisfaction of finding it yourself.

Firstly, have a look at the species Fact Sheet. Also look at the messages attached on the bottom of that page as there is a lot more information included there. Also have a look at Page 2 for more messages. Make sure to follow the underlined links to further information. Also look at the paragraph on Deimatic Display in the Nudibranch Colour Page.

Good Luck with your project,
Best wishes,
Bill Rudman

Dear Danny,
This animal is very easy to misidentify. It looks very like Chromodoris decora or one of the other very similarly coloured species. It is however a juvenile of Hexabranchus sanguineus. [See message 1, message 2 for more photos].
Best wishes,
Bill Rudman

Dear Shawn,
Sorry but I can't give you good news. The biggest problem is that aquarium/pet shops should NOT stock nudibranchs unless they know precisely what the species they have eats, and have a ready supply of the food available. Imagine the outcry if they could not provide the right food for all the fish they sell. By stocking nudibranchs and selling them to customers, they are essentially condemning them to starvation and death. They are also ripping off their customers as well by selling you animals they know will die.

Have a look at some of the earlier messages on Hexabranchus, which are attached below yours on the Hexabranchus page [see also Page 2]. You will see they do eat a variety of sponges, but even if you went out on a reef and collected some sponges yourself, there is no easy way for you to identify if any of the sponges you have found are ones that the nudibranch eats. There would also be the difficult job of getting the sponges back to your aquarium alive and healthy, and then the job of keeping them alive in your aquarium while they are being eaten. Concerning the egg mass. Laying eggs is not necessarily a sign of well-being, in fact often it seems to be a sign of stress. Will the eggs hatch? Sometimes, especially when stressed, the eggs are infertile. Even if fertile, Hexabranchus produces free-swimming planktonic veliger larvae, which need to swim for some time in the plankton, feeding on microscopic plants. Such veligers rarely survive in normal aquarum setups. And since the larvae settle on their food when they are ready to become slugs, we are back to the food problem.

Sorry I can't give you better news,
Bill Rudman

Thanks Constantine,
Bill Rudman

Dear Jason,
Yours is an interesting question. It is based on the similarity of the ruffled edge of the slug's mantle to the edge of the dress of a Spanish Flamenco Dancer. However I have no idea where the name was first used, or who made it up. It is one of the few common names which is in fact used commonly, and unambiguously refers to Hexabranchus. If anyone can find an early reference 1950s? 1960s? or before, please let us know.
Cheers,
Bill Rudman

Dear Valeria,
What a beautiful place to live. I guess it is also a good place to see if you can keep nudibranchs alive in your aquarium because you can always put them back in the sea if things don't work out. I am not sure how long it takes Hexabranchus to grow so big, but if you are fortunate to get the right sponge for your 6 cm animal I am sure it will live in your tank for some time before you have a space crisis.

If you have photos or observations on sea slugs from the Comoros they would be very welcome.
Best wishes,
Bill Rudman

Thanks Mary Jane,
They certainly don't look much like a Hexabranchus at this size, do they? Best wishes,
Bill Rudman

Dear Marina,
The bright red colour of your animal certainly lives up to the species name -sanguineus - which is derived from the Latin word for blood.
Best wishes,
Bill Rudman

Dear Student,
Hexabranchus seems to feed on a variety of sponges. The most extensive list of sponge species apparently eaten by it is in a study by Francis (1980).
• Francis, M.P. (1980) Habitat, food and reproductive activity of the nudibranch Hexabranchus sanguineus on Tongatapu Island. The Veliger, 22(3): 252-258. (Figs 1-4)

He reports that it eats Ancorina acervus (Bowerbank), Callyspongia sp., Cliona sp., Haliclona sp., or Adocia sp., Mycale sp. , or Zygomycale sp., Pachastrella sp., Paraesperella sp., Petrosia sp., Stelletta sp., and Xestospongia exigua (Kirkpatrick). Others have reported it eating species of Halichondria sp. and Leucetta solida.

As to what eats Hexabranchus, I have no idea. Fish probably try to eat it but if you look at the section on Deimatic Display in the Defensive Colouration Page you will see that we think that they may be able to frighten off curious fish by startling them with their bright colour pattern.

I hope this helps you with your project
Best wishes,
Bill Rudman

Thanks Stuart,
Bill Rudman

Dear Stuart,
I have kept these photos separate because they show the peculiar and unique, hand-like oral tentacles found in Hexabranchus. In the upper photo we can see how all the 'fingers' are touching the surface of the rock, presumably giving the slug sensory information as it crawls along.
Best wishes,
Bill Rudman

Dear Reine,
Yes these are Hexabranchus sanguineus. At present we consider that there is only one species in the Indo-West Pacific but if you look at the other photos on this page you will see that there are a number of distinctive colour forms which probably need to be looked at in more detail before we can be sure.

Your 25cm animals are quite large but Marli Wakeling in an earlier message reports some at about 60cm long.
Best wishes,
Bill Rudman

Dear Allan,
I am pretty sure this is strange colour form of Hexabranchus sanguinea or perhaps a distinct species? Have a look at the photo of a blue Hexabranchus from Bob Bolland in Okinawa. It is very similar. It seems in your photo that each gill has a separate insertion into the body wall, which is a characteristic of the Family Hexabranchidae. At present only one species of Hexabranchus is recognised, but this may change as more material become available for research.
Best wishes,
Bill Rudman

Dear Joyce,
Hexabranchus is a sponge feeder, so it would be unusual for it to eat other things even in aquarium conditions. So the most likely thing is that it will slowly starve. Unfortunately there is no way it will remain happy and healthy if it can't find appropriate food. The red ring you mentioned is almost certainly an egg ribbon - unfortunately laying an egg ribbon like this is often another sign of stress.
Sorry I can't offer better advice
Bill Rudman

Dear Belinda,
The scientific name of the Spanish Dancer is Hexabranchus sanguineus. If you click on that name you will be taken to the first of 2 pages with information and messages on the Spanish Dancer. For example if you scroll down the page beneath this message you will find earlier messages arranged in date order. If you look through all the messages you will find lots of information and beautiful photos of this fascinating nudibranch.

For more general informaton on nudibranchs click on the General Topics button at the top of the page (or in the yellow bar above) and you will get an index of more general topics. Hope this will help your daughter in her project,
Best wishes,
Bill Rudman

Dear Luigi,
Thanks for these beautiful photos of Hexabranchus swimming. Your photos clearly show the complex nature of its swimming ('dancing') movement. It is a combination of a dorso-ventral flexing of the whole body and a muscular wave which runs along each side of the mantle, causing the wing-like flapping of the mantle edge. It is amazing how long they can continue to 'dance' before tiring. I have watched one swimming for over an hour. Has anyone else made any observations on how long they can swim?
Best wishes,
Bill Rudman

Thanks Luigi,
Bill Rudman

Thanks John,
Bill Rudman.

Dear Scott,
Thanks for this nice series of photos. They certainly show the progression to a more 'Spanish Dancer' looking animal.
Best wishes,
Bill Rudman

Dear Scott,
I wondered how long before the colour 'forms' of Hexabranchus became a talking point on the Forum. I'll keep them all under the 'umbrella' of Hexabranchus sanguineus, but as Bernard Picton would almost surely say, this is a question we might invite the molecular chemists to have a look at. I like the egg mass difference.
best wishes,
Bill Rudman

Dear Scott,
Thanks for these photos. The difference from 'typical' H. sanguineus is indeed quite marked.
Cheers,
Bill Rudman