Dear Paul,
This is a rather shy looking Hexabranchus sanguineus. In fact the Spanish Dancer is only a spectacular 'dancer' when it trying to escape from danger. Normally it sits like this, looking quite camouflaged and nonedescript. It is only when it unfolds the sides of its mantle to show the bright red and white colour pattern is it instantly recognisable. See the Colour in Sea Slugs page for further information.
Best wishes,
Bill Rudman

Dear Paula,
An animal that large, and red, is most probably a Spanish Dancer [Hexabranchus sanguineus]. If you look through the messages on the Hexabranchus page you will see quite few photos of different colour forms. Concerning the gills. In most dorid nudibranchs with a relatively flattened body [eg Discodoris, Platydoris, Jorunna etc] the gills all contract into a single gill pocket. In Hexabranchus there is no gill pocket and each gill is inserted independently into the body wall. However when the gills are all extended it is hard to see the basal region and until they are maximally retracted it is difficult to see that they are independent of each other.

For future reference, one sure way of identifying Hexabranchus is to have a look at its mouth. Instead of having a single oral tentacle on each side, it has flap of tissue with a number of finger-like projections. Another fairly convincing test is to see if it will swim with the characteristic dorso-ventral muscle waves along the body.

Off-hand I can't think of any other uniformly dark red nudibranch of that size. Without some more clues I can't really help. Did anyone touch it? was it soft and fleshy or hard and rough? etc etc.
Best wishes,
Bill Rudman

Dear Anuschka,
This certainly looks like a chromodorid but although I have not seen this colour form before I am pretty sure it is a juvenile Hexabranchus sanguineus - the Spanish Dancer. In adults one character of Hexabranchus is that each gill is separately inserted into the skin of the body wall. This is not so easy to see in live juveniles, although it is usually clear when they are dead and preserved. One clear external difference from most chromodorids is that the gills are branched, which you can see in your photo.

If you look through other messages on this page you will see the red patches on the back are quite consistent in many colour forms. However the yellow border in your animal is an unusual variation. One other feature found only in Hexabranchus is the shape of the oral tentacles on either side of the mouth. Instead of being a single tentacle or flap of tissue, each 'tentacle' is a handlike flap with a series of fingers. I will try and find a photo and post it on the Forum. Unfortunately it is not a feature you can see in photographs of the dorsal surface.
Best wishes,
Bill Rudman

Dear Friedrich,
Hexabranchus certainly doesn't produce the royal purple dye. I have discussed the origin of this 'Tyrian Purple' in a couple of messages [message 1, message 2]. Have a look at them for some background information. Sea Hares also produce a purple ink but it is not used in producing dyes.
Best wishes,
Bill Rudman

Dear Drew,
The scientific name of the Spanish Dancer is Hexabranchus sanguineus. If you look at the other messages on this page you will see it has quite a colour range and can grow to a very large size.
Best wishes,
Bill Rudman

Dear Jochen,
Thanks very much for the photos. The Red Sea Hexabranchus is definitely very red. Has anyone any photos of a Red Sea Hexabranchus that is not this uniform red colour?
Best wishes,
Bill Rudman.

Thanks David,
This animal was first described from an animal collected in the Red Sea. The name 'sanguineus' means 'bloody' or 'blood red', which is very appropriate for this deep uniform red colour form found in the Red Sea.
Bill Rudman.

Thanks Dave,
They are really spectacular when they are 'dancing / swimming'.
Bill Rudman

Dear David,
Yes it is a small Hexabranchus sanguineus. When they are very juvenile they look very like a species of chromodorid. Have a look at Mike Miller's photo in an earlier message
Bill Rudman

Dear Alicia,
The Spanish Dancer's scientific name is Hexabranchus sanguineus. In the Forum each species has its own page, and messages about a species are all on that page. So I have put your message on the Hexabranchus Page.

If you look above your message you will find some photos and general information on the Spanish Dancer and if you look below your message your will other messages about it. Many of these messages have nice photos of animals from different parts of the pacific and Indian Oceans. If you look at all htat information I think you will find all the information you will need.

One thing I don't think you'll find is why its name is Hexabranchus sanguineus. Hexabranchus = six gills and sanguineus = blood and refers to its red colour.

I am not sure how much you know about using websites. One useful thing to know is that if you click on any word or group of words that are coloured and underlined, you will go to a new page which is about the word you clicked on.

Best wishes,
Bill Rudman.

Thanks Marli,
At a rough conversion that is about 60cms. Definitely beats the 52cm I mentioned before.

As Sydney is the home of the Olympics as well as the Sea Slug Forum, can I mention that in the Olympic Games opening ceremony they had an underwater world sequence, and apart from the usual fish and jellyfish I was pleased to see a swimming Hexabranchus! Not what I would call a gold medal swim but as the commentator's are saying as their favourite misses out on a medal, it was a "a creditable performance".

Best wishes,
Bill Rudman.

Dear Leticia,
You certainly chose a spectacular invertebrate to study. Have a look at all the messages and photos of Hexabranchus above and below your message. You will find quite a lot of information there. If you are able to visit a library that has the scientific journal The Veliger there is a very good article which has all the information you would need:
• Francis, M.P. (1980) Habitat, food and reproductive activity of the nudibranch Hexabranchus sanguineus on Tongatapu Island. The Veliger, 22(3): 252-258.

Perhaps your teacher or one of your parents could help you find it, as The Veliger is an American scientific journal which most museums and university libraries should have.

Basically all sea slugs are hermaphrodite. That is they have a full set of male and female organs. They don't fertilise their own eggs however, but every time they mate they are able to give and receive sperm, so doubling their opportunity to pass on their genes. They lay a large frilly pink egg mass with thousands of tiny eggs which hatch out as free-swimming veliger larvae, which swim for some time in the plankton before settling down and turning into tiny crawling slugs. Use the SEARCH button to find information on veligers [type veliger]. You will also find a photo below of a very small Hexabranchus which looks quite different from the adults, and is unable to swim.

I hope this will help you with your project. Have a look at some of the General Topic pages for some more information on nudibranchs.

Good Luck with your project,
Best wishes,
Bill Rudman.

Dear Bruce,
Firstly thanks again for the beautiful shots of Melibe leonina.

Concerning your large nudibranchs. Although I don't think there has been any anatomical study undertaken, the prevailing view is that they are very very large Hexabranchus sanguineus. I have previously mentioned on the Largest, heaviest, etc page of reports of Hexabranchus growing to at least 520mm in length off Djibouti in the Red Sea (Double, 1992). I have also seen photos of very similarly sized animals from deepwater off Fiji. Interestingly these large animals all seem to have a very similar colour pattern. On a rough conversion your 18 inches equals about 45cm, so your animals are definitely of similar size to those from the Red Sea give or take a bit of stretching.

Thanks for these great shots Bruce. I had been thinking that since in 2 weeks time Sydney is going to be swamped by the Olympic Games this would be a good time to make a call for some messages about the biggest, shortest, longest etc sea slug. If anyone has any candidates I'll of course need some photographic evidence so no fishermen's tales please.

Best wishes,
Bill Rudman.

Reference: Double, T. (1992) Here be Giants. BBC Wildlife, 10(5): 34-40.

Thanks Erwin & Britta,
Bill Rudman.

Dear Valda,
It is a juvenile Hexabranchus sanguineus. I'm glad you mentioned it swimming, as I have often wondered at what size it began swimming. Have a look at Mike Miller's message and photo of an even smaller one.

You are not the first to be fooled by these juveniles. I was pretty sure it was a chromodorid some years ao when I was reviewing Chromodoris decora and similarly coloured species. The separated gills seemed a bit strange but it wasn't until I looked at the radula and couldn't find a reproductive system that I realised what it was.

Best wishes,
Bill Rudman.

Thanks Bob,
First time I have seen a blue one. Is it unique or uncommon or do you find it often?
Cheers,
Bill Rudman.

Dear Brandon,
There was a paper some years ago by by Francis (1980) on aspects of the life history of Hexabranchus. I am not 100% certain, but I think he had some information on how old they were when they began egg laying.

It is in in The Veliger. I'm afraid I am working from home for a few days and don't have the paper available. Have a look at the page of references on Hexabranchus biology for a citation.

Best wishes,
Bill Rudman.

Dear Roy,
The Spanish Dancer, Hexabranchus sanguineus, grows to quite a large size, and like most dorid nudibranchs, it feeds on only a few species of sponge. To keep it alive successfully you would need to identify its natural sponge food, or find an alternative that it would eat. You would then need to have an easily available continuous supply of the sponge for food.

Have a look at the information on Hexabranchus above your message on this page, and at the earlier messages and discussion on Hexabranchus which are below your message on this page. You will also find a link to a page of references on its biology and natural history.

Best wishes,
Bill Rudman.

Thanks Mary Jane,
Bill.

Dear Mary Jane,
Was this a big animal? Some of the larger specimens, especially from deeper sites are often a more uniform pink colour like this.
Best wishes,
Bill Rudman.

Dear Marco,
I'm afraid not. Perhaps someone reading this will let us know if they have seen one.
Best wishes,
Bill Rudman.

Dear Danielle,
I guess the Saipan your are talking of is in the Northern Mariana Islands north of Guam. Sounds a great place to find nudibranchs.

I have prepared a list of references on Hexabranchus sanguineus for you. Hopefully you will be able to obtain a few of these. The one by Francis in The Veliger is quite comprehensive.

In brief, Hexabranchus can be found in tropical waters worldwide from the intertidal to quite deep water - deeper than scuba divers can safely venture. It is a sponge-feeder but does not seem to be a specialised feeder on a particular species of sponge. The skeletal spicules of many encrusting sponges have been found in its stomach. Hexabranchus seems to breed all year, though in the Red Sea it is reported to stop breeding during the coldest period of the year. The bright red egg ribbons are quite characteristic.

Like many nudibranchs, Hexabranchus seems to be protected somehow from fish predation. The bright red colour on their mantle has long been considered a 'warning' colouration to fish. In the last ten years or so we now have evidence to show that Hexabranchus has distasteful, and potentially toxic, chemicals in its body and egg masses. These chemical molecules (macrolides) are almost identical to antifeedant chemicals found in Halichondria, one of the sponges that Hexabranchus eats. The sponge produces the molecules to protect it from fish predation. It is thought that Hexabranchus obtains the molecules from the sponge during feeding, and after modifying the structure of the molecule slightly, stores them in its skin and egg masses for its own protection.

I hope this will help you with your project. You will also find more information in the other messages about Hexabranchus below yours on this page. Also have a look at the Index of general topics for more information on other aspects of dorid and nudibranch biology.

Best wishes,
Bill Rudman.

Dear Emily,
Where in the world is South Padre Island? Although the internet brings us all closer together it is still a very big planet. As each region has its own unique nudibranchs, I could give you a better answer if I knew which part of the world we're talking about. Have a look at the page on the Spanish Dancer. There is some information at the top of the page and if you move down through the messages you will find a spectacular photo from Wayne Ellis of it swimming. It gets it name 'Spanish Dancer' from the resemblance of its red and white edged 'ruffled' mantle, to the dress of a Spanish Flamenco Dancer.

However the Spanish Dancer is found in the tropical Indian and West Pacific Oceans. If South Padre Island is in California, or your animals didn't look like the photos here, perhaps you should let me know and I'll try again. Perhaps you could tell me a little about its shape and colour.

Best wishes,

Bill Rudman.

Dear Ernest,
Thanks for this and the other photos you have sent. I will be posting them on the site when I organise answers. From one of your earlier messages I guess Treasure Beach, and the other collecting localities are in Durban, KwaZulu Natal.
Best wishes,
Bill Rudman.

Dear Mike,
Yes its a juvenile Hexabranchus sanguineus. It's a bit hard to see from the photo but each gill is separately attached to the mantle, just as in the adults, and of course its radula is quite different.

It has a remarkable resemblance to some purple spotted chromodorids such as Hypselodoris maculosa, Thorunna australis and Chromodoris decora.

Reference: Rudman, W.B. (1986) The Chromodorididae (Opisthobranchia: Mollusca) of the Indo-West Pacific: Noumea purpurea and Chromodoris decora colour groups. Zoological Journal of the Linnean Society 86(4): 309-353.

Bill Rudman.

Dear Tatiana,
In answer to your question, have a look on the Hexabranchus sanguineus Page, both above and below your message, and you will find information on the Spanish Dancer and how it got its name. If you have further questions, let me know.
Good Luck with your project,
Bill Rudman.

Awaiting a reply from Bill.

Peter Firminger
Web Manager

Thanks Wayne,
What a spectacular photo. They are really amazing swimmers. I don't know how they can keep going for so long. I have seem them flapping their mantle 'wings' non-stop for over an hour! - and if they don't keep flapping they sink.
Bill Rudman.

Thanks very much Erwin.
Bill Rudman.

Dear Caleb & Jamie,
I am pretty sure you are describing Hexabranchus sanguineus, and perhaps the yellow colour form I have illustrated above. Usually this species has a brilliant red and white colour pattern and hopefully someone kind will send us a photo to put on the Forum. Hexabranchus is often called the Spanish Dancer because the frilly edge to its mantle looks like the dress of a Spanish Flamenco Dancer.
    
The "wings" your describe are really part of its back or 'mantle'. In the more common red colour form, the upper side of the mantle is brilliantly coloured in red and white, while the underside is a dull mottled colour of pinks, browns and whites. When Hexabranchus is quietly crawling along, its 'wings' are folded over the rest of its back, covering the brilliant colour pattern with the dull mottled underside. When it is disturbed, however, - poked, prodded, nipped etc, it will quickly unfold the mantle to display its bright colour pattern. It then starts to vigorously flap its 'wings' and swim away.  Its swimming is basically an escape mechanism and the sudden display of the bright colour pattern is thought to have evolved to startle potential predators such as fish. See the pages on the Forum describing the use of colour in defence and especially 'deimatic colour display'

The tentacles at the front are rhinophores, which it uses to 'smell' its food, and the anemone-looking things on its back are its gills which it uses for breathing.

Hexabranchus, feeds on a variety of sponges.

Best wishes,
Bill Rudman.