Thanks Barbara,

I wouldn't be surprised if this is the egg mass of this animal, as most of the 'colour forms' or species I am lumping in Hypselodoris bullocki [and H. apolegma] have this shaped and coloured egg ribbon [see message #7110] .  Interestingly, the photo your refer to [#12058] has a rather sinuous ribbon with multiple coils rather than the stiff ribbon of about one and a half coils which yours has. The  ribbons I have seen are usually as in your animal, but as you will see on the Forum, sometimes there are multi-coiled ribbons and they are not confined to a specific colour form.

I was interested in your suggestion that this species tends to  congregate in one spot. While this may be the result of some peculiar physical conditions -such as light or water currents - I wouldn't be surprised if it coincided with the presence of its food sponge or perhaps a large concentration of the food sponge at that site. Perhaps there are good growing conditions for the sponge at that spot. Have a look at photos in messages #19355; #16260 for good photos of its favourite food Euryspongia.

Best wishes,
Bill Rudman

Thanks Marcel,
It looks like the colour in this colour form or species varies from a very dark blue to the lighter colour in your photos. The broad white band around the mantle edge is reminiscent of Hypselodoris apolegma [see #19710] but in H. apolegma the white border does not have the distinct inner edge that your animals have. But as I have discussed before, is H. apolegma really a distinct species?

Because of this difference to the mantle border, I have kept specimens such as yours [see #2073, #1747, #2274, #18974, #16653] as part of the H. bullocki group. One other point is that the gill colour of these blue ones differs from orange, as in your animals, to deep blue [#20665]. What it all means, I have no idea. Some years ago I tried without success to find anatomical differences between different colour forms, and as you will see on the Forum ,we have at least two examples of different colour forms, or species, mating [see #6816, #20968]. Mating only with ones own kind is a basic tenet of the species concept. If the different colour 'forms' are different species, then H. apolegma is surely a particularly incompetent species.

Best wishes,
Bill Rudman

Dear Kenneth,

Concerning the rhinophores, I am not sure if your is one with blue rhinophores rather than yellow - if so, they could just be retracted.  Another possibility is that some fish as bitten them off - if so it should be able to regrow them.  I am not sure just what the limits of Hypselodoris bullocki are. I have continued to include this blue form with a broad white border as a colour form of H. bullocki, but I am sure someone is itching to name it as a new species. It has at least 3 colour forms, one in which the rhinophores and the gills are the same colour as the body [see message #2073, #15410], another which has yellow (or orange) gills and rhinophores [message #1747]; and a third which  has yellow (or orange) rhinophores and blue gills [message #18974]. Similar variability can also be seen in the pinkish animals with a narrow white border.

Concerning possible feeding. The pink lump the animal is on is in fact a plant. It is what we call a coralline algae. Thewse algae are a group of red algae which accumulate calcium carbonate in their tissues. Some grow jointed 'fronds' a bit like the green alga Halimeda, while others - like in your photo - slowly deposit layers to form lumpy 'rocks'.

I'm glad to see the Forum is a force in uniting slug fanatics worldwide.

Best wishes,
Bill Rudman

Dear Ben,

Good question - but you are confusing various levels of information. Although I didn't know exactly what they ate I certainly knew that they didn't eat plant material. From my knowledge of the anatomy of this family of nudibranchs it is quite clear that they are carnivores not herbivores. Just like a mammal expert can distinguish  carnivores from herbivores from aspects of their anatomy, an expert on molluscs can do the same with sea slugs. In fact all nudibranchs are carnivores, which makes the advertisement from Aquacon that they have 'nudibranchs' which 'will take care of your algae' quite irresponsible and quite incorrect.

Since that message was posted in 2001 I have published a research paper which brings together all the information we have on precise food choice in this family (Rudman & Bergquist, 2007) which shows that Hypselodoris bullocki and closely related species feed exclusively on sponges of the genus Euryspongia (Fam: Dysideidae). However knowing this name or even the precise species of sponge they eat is of little value to aquarium enthusiasts because sponges are extremely difficult to collect and keep alive in aquaria, even if the collectors could correctly identify the species. Also, if you had the right sponge, and found just the right conditions to keep a colony alive in a tank, your aim is basically to sabotage your sponge husbandry by letting a nudibranch loose on this fragile sponge colony to eat it alive! Damaged sponges quickly rot and die and produce or release toxic chemicals into the water which will soon foul your aquarium. I have said this many times before so have a look at the messages listed under Keeping Sea Slugs in captivity for more comments on the topic.

• Rudman, W. B. & Bergquist, P. R. (2007) A review of feeding specificity in the sponge-feeding Chromodorididae (Nudibranchia: Mollusca). Molluscan Research, 27(2): 60-88

Best wishes,
Bill Rudman

Dear Bob,
This is either an example of one species with a very variable colour pattern, or a group of similar species.  I am at present lumping most of them together as Hypselodoris bullocki until a more convincing solution is proposed.

Best wishes,
Bill Rudman

Dear Richard,
Thanks again. Although we do have a number of records of this species feeding, it is not many in comparison with our knowledge of feeding in other animal groups. It looks like this species specialises on the dysideid sponge genus Euryspongia but I am reluctant to say we have enough evidence just yet. The little clump of sponge in your photo well illustrates the problem of building up feeding information, because often the sponge colonies are not obvious like in Poppe's message [#16260] but very small, or partly covered in temporary mud or debris and so difficult for us to see.

Your photo of sponge fragments travelling down the oesophagus to the stomach is pretty indisputable evidence.

Best wishes,
Bill Rudman

Dear Richard,
Yes this is the 'typical' colour form of Hypselodoris bullocki. You will see there are a number of colour forms with this rather high, narrow, body. There is some debate over whether they are a group of related species or one species with a number of colour forms. I am always interested in photos of these animals feeding,as they are helping us to build up information on their natural history and to find out just how specific each species is when it comes to diet. Your photo clearly suggests that these two are busy feeding on a sponge, but as often happens, the sponges in your photo are obscured by both the slugs and overgrowths on the sponges.

Best wishes,
Bill Rudman

Dear Asther,
Thanks for this record. This 'species' or 'colour form' is certainly very distinctive.

Best wishes,
Bill Rudman

Dear Charles,
Yes I would call this a colour form of H. bullocki.

Best wishes,
Bill Rudman

Dear Leslie,
Thanks very much for the background information. As you may have noticed, I am very weak when it comes to following my own rules on only answering questions on sea slugs. Any slight connection usually leads me astray. Unfortunately we usually only get to study our particular animal group after they are dead and preserved, so I take any opportunity to build up information on them as living things.

Best wishes,
Bill Rudman

Dear Brian,
It's nice to know at least one of my explanations is credible! I've seen these little worms in action before. I am not sure if they are just fierce protectors of their 'home' or whether their survival strategy is to have a quick bite at anything that passes by. Whatever it is, it certainly deters Hypselodoris.

Best wishes,
Bill Rudman

Dear Brian,
Nothing's ever simple! I am pretty sure that Hypselodoris bullocki feeds only on the dysideid sponges of the genus Euryspongia. The purplish object is a small sponge colony and from its general shape I would say it could well be a dysideid. However I can't see enough detail to be sure. If you look on the Fact Sheet, and the recent message [#16260] from the Poppes, you'll see that Euryspongia has a very characteristic arrangement of fibres.

As to the animal not staying to finish the meal. I suspect it was not so much the sponge that was not to its taste but the 'wildlife' on the sponge. In the close-up alongside you  can see at least one polychaete worm apparently disturbed by the nudibranch's presence. When sponge colonies are large they are often quite clean of other animals, but when they are small they are often home and or substrate to worms, crustacea and other invertebrates. Nudibranchs are often quite sensitive to pokes, prods, bites and even stings from other animals, and I suspect this may be the case here.

Best wishes,
Bill Rudman

Dear Kerem,
Firstly this species is part of what I have been calling the Hypselodoris bullocki group, for want of a better name, but I don't think it is actually Hypseldoris bullocki or H. apolegma. It will probably need a new name. For convenience I am leaving these unnamed species which look quite like H. bullocki with that species until they are sorted out.

As to its feeding. Although it looks like it couold be feeding, in both cases I am pretty sure the pinkish thing it is on is a large sea squirt or ascidian. certainly in the middle left photo there are small ascidians in the background and it is crawling over some middle-sized ascidians, so I am pretty sure that the bit in the foreground of that photo is also an ascidian. I have had a careful look at your hi resolution photos and there is no sign of the texture and pores that you would expect to see in a sponge.

Best wishes,
Bill Rudman

Dear Guido & Philippe,
Thanks for these photos of H. bullocki on the same sponge as I photographed it on in New Caledonia [see Fact Sheet], which has been identified by Pat Bergquist as a species of Euryspongia. The two records again show how variable growth form can be in sponges. the upper photo showing a sponge with quite delicate radiating ridges which are invisible in most of the other sponge except for a small place on the close-up [middle right photo].

Best wishes,
Bill Rudman

Dear Jim,
I'm afraid the only food that will keep them alive is the right sponge. Glad you like the Forum
Best wishes,
Bill Rudman

Dear Asther,
As you'll see from other messages on the Forum [see #12058], I have kept this colour form with the more typically coloured animals we identify as H. bullocki, mainly because I am not sure how many species are involved. I looked at the anatomy of mnay of them some time ago but couldn't find any good differences. One colour form has been considered a distinct species [Hypselodoris apolegma] but I can't say I am 100% convinced, especially when we have Phil Slosberg's photo [#6816 ] of  two colour 'forms' or 'species' mating. I think we need some more anatomical data before we can be sure. This is a good example of how much we still have to learn about many of these animals. As I often say, photos showing egg-laying, mating, and feeding are very valuable because they can sometimes give us clues to differences between similarly coloured animals, and so suggest where we should be looking for possible species' differences
Best wishes,
Bill Rudman

Dear Paul,
A very interesting find. I have in the past considered these to be colour forms of one species, but I know some people would like to make them distinct species. What is particularly interesting is how the smaller one is developing a purple band at the front of the mantle and also on the posterior tip of the foot. I assume this means it is gradually chnaging colour to purple. I had previously discounted a colour change like this as I had found small purple animals and large whitish ones, but I guess this suggests animals can change colour, or at least gain colour, at different sizes.
Best wishes,
Bill Rudman

Dear Matthew,
By coincidence we have had a few messages about this dark blue 'form' of H. bullocki recently. The yellow object is this animal's egg ribbon. It's most probable that the eggs, if there are eggs in the ribbon, are infertile. Unhealthy animals often lay eggs like this before they die, almost as though they are trying to leave some descendants. I don't know if your local fish store told you that these animals are specialised sponge feeders, and it is most unlikely that the store can provide you with the right food. One good thing is that the egg ribbon is a useful piece of information and looks very like a photo in an earlier message. If you look at some of the earlier messages about H. bullocki you will see we still are not sure just which colour 'forms' are different species and which are just variations. It may be that some of the diffferent colour forms can be distinguished by the shape and colour of their egg ribbons, even if we can't find good anatomical differences.
Best wishes
Bill Rudman

Thanks Fredy,
I have not seen many examples of this deep blue coloured 'form' so any photos showing variability are welcome.
Best wishes
Bill Rudman

Thanks Mary Jane,
Thanks for keeping the H. bullocki puzzle in mind, but as you have discovered they certainly don't want to give away their secrets easily.
Best wishes
Bill Rudman

Thanks Gary,
This is excellent evidence of it feeding. In the upper photo we can clearly see a feeding scare around its head, and I have included a close-up alongside to show more clearly the feeding scar in the bottom right of your whole photo. I am already trying to get a positive identification on the sponge
Best wishes
Bill Rudman

Dear Ray,
This is one of a group of 'species' which I still have on the H. bullocki pages. It is quite similar to the one which has been described as H. apolegma, but in that species there is a white network between the white border and the purple colour of the rest of the mantle
Best wishes,
Bill Rudman

Thanks Erwin,
I think you may have interrupted a happy meal for nothing. I am pretty sure the 'apolegma-like' animal is not what Yonow has described as H. apolegma. In her animal there is a distinct white reticulate pattern between the white border and the purplish mantle. In this animal the junction is abrupt. It has similarities to H. flavomarginata but in that species the margin is yellow and there is a thin opaque white line between that and the pink/purple of the rest of the mantle. At the moment you'll find other photos of this 'colour form' scattered through the H. bullocki pages, although I suspect it's another species.
Best wishes,
Bill Rudman

Dear J.B.,
This is one of the 'colour forms' of Hypselodoris bullocki. If you look through the earlier messages on this species you will find other photos with this colour pattern. At present we don't know whether there is one variable species or a number of similarly coloured species. What we are confident about is that they are all sponge feeders NOT algal feeders.
Best wishes,
Bill Rudman

Dear j.b.mcclung
It is impossible to identify things seriously without a fuller description and preferably a photo. It could come from any ocean in the world. If its bright purple it is almost certainly a nudibranch so in spite of what your 'lfs' has told you it will NOT be an algal feeder, so if you buy it you will be sentencing it to a slow death by starvation. It is possibly Flabellina iodinea which is definitely not a herbivore.
Best wishes,
Bill Rudman

Dear Chris,
Your slug is a colour form of Hypselodoris bullocki, and the 'noodle-like thing' is its egg ribbon. Often when under stress these slugs will lay an egg ribbon. It may be infertile, and even if the eggs hatch, the larvae are unlikely to survive in aquarium conditions. A number of earlier messages have good photos of the egg ribbon.
Best wishes,
Bill Rudman

Dear Tana,
Firstly, with a little luck I can identify quite a few things from very little information, but I can't work miracles. I can't even guess at your egg mass without a photo or a drawing, or even a few words of description. Its a bit like saying "I have bought a colourful fish - what shall I feed it?" Basically, if you want any sensible information or advice, you have to give me some real clues.

If you have a look at the messages on the H. bullocki page [and pages 2,3] you will see a number of photos of its egg ribbon. If your second species is C. magnifica, then go to the page which describes the flat egg ribbon found in some chromdorid species, including C. magnifica. If your second animal is that species, then you should be able to identify who producd the egg ribbon, as C. magnifica's ribbon is flat.

Now to your other points. Have a look at the List of General Topics for places where I discuss aspects of larval life, and the chance of them surviving in home aquaria. It is not high. Also there is no guarantee the eggs in this ribbon are fertile. Often sick and stressed animals lay eggs ribbons before they die - perhaps a futile attempt to produce a new generation.

Concerning feeding your nudibranchs. You say you have a 'sponge' to feed them. Its like saying you have a 'leaf' to feed a caterpillar. Nudibranchs, like caterpillars, are incredibly choosy. Each species has a particular sponge on which it feeds. I guess its possible, but most unlikely, that you two nudibranchs will eat the same sponge. I am sorry to sound negative, but as I have said many times before, aquarium shops should not be selling nudibranchs. They are just condemning them to a slow death by starvation.
Best wishes
Bill Rudman

Thanks Mary Jane,
It's not often you see such major size differences in mating pairs of nudibranchs, although pairs of quite small individuals are not uncommon. As I have said before, many opisthobranch exhibit what we call protandry, a developmental process in which the male reproductive system, in these hermaphrodite animals, develops much more quickly than the female system. We assume that in matings such as this, the sperm being passed to the smaller partner will be stored in a sperm sac until the animal's female system matures. This is a useful adaptation for animals which meet only by chance.
Best wishes,
Bill Rudman

Thanks Marina,
At the moment there is still plenty of room for colour 'forms' of H. bullocki.
Best wishes,
Bill Rudman

Dear Michael,
The main colour feature distinguishing H. apolegma from typical H. bullocki is the broad opaque white mantle border in H. apolegma, which on the inside edge has a reticulate region of white which can be seen in Phil Slosberg's photo alongside. I would consider your two animals to be dark and pale variations of 'typical' H. bullocki. It would be nice if it was a repeat of Phil's observation but we can't always be lucky.
Thanks again for looking,
Bill Rudman

Thanks Alice,
Bill Rudman

Dear Kheong,
The reason the gills look smaller in the white one is because they are partly withdrawn into a pocket on the back of the animal. The dorid nudibranchs are divided into two 'Superfamilies' - the EUDORIDOIDEA and the ANADORIDOIDEA. One of the main differences between the two is that in the Eudoridoidea the gills can be withdrawn into a pocket for protection. Another name for the superfamily is the 'Cryptobranchia' which basically means 'hidden gills'. In the Anadoridoidea there is no pocket into which the gills can be withdrawn, although the gills can retract against the body when the animal is disturbed. Another name for this group is the 'Phanerobranchia' which means 'visible gills'.

You can see from the Species List which dorids belong in which superfamily. There is some debate about whether this division reflects evolution or is just a convenient way of splitting the dorids into two, more manageable, groups.
Cheers,
Bill Rudman

Dear Kheong,
Thanks for these. I have split your photos of purple and pink animals into separate messages.
Cheers,
Bill Rudman

Dear Kheong,
Thanks again. These photos show 'typical' on its food sponge. The white patch on the sponge probably indicates some feeding damage.
Best wishes,
Bill Rudman

Thanks Kheong,
When I saw your message title I thought this was going to be a photo like Phil Slosberg's showing typical H. bullocki and 'Risbecia apolegma' mating. However your photo shows two 'shades' of 'typical' H. bullocki mating. Not quite as exciting but a nice piece of comfirmation.
Best wishes,
Bill Rudman

Dear Ike,
I had forgotten about my bird seed comments. Sorry you have had to find out the hard way. I am sure most aquarium shop owners like animals so the only way to stop this trade is to do what your are doing - let them know that what they are doing and saying is wrong.
Good luck,
Bill Rudman

Dear Erwin,
Thanks for drawing my attention to this photo. I have contacted Phil Slosberg who has given me permission to post a copy on the Forum. I asked him if the photo was 'posed' or 'natural' and he replied:
"As to background, this was a pair that I just happened to come upon in flagrante delicto nudibranchio. It is the first and only pair of such divergent color variation and size that I have ever encountered. I would assume it to mean that since they mate, they are color variations of the same species rather than different species, but I would be very interested to hear your more learned views on the matter". .. Phil Slosberg

This is a rather interesting photo as it certainly raises the question of how we define a 'species'. This is not a close 'look' at each other, or even an exploratory 'jab' with the penis. This appears to be two animals mating. As Clay Carlson notes in a separate message, this white bordered colour form has recently been named as a new species. This photo certainly gives us something to think about.
Best wishes,
Bill Rudman

Dear Kheong,
In this photo you have 2 animals mating and a third one at the top which is probably a different species. The mating pair are definitely Hypselodoris bullocki. At the moment I have included the third animal on the H. bullocki page until we sort out just how mnay species there are in this complex of similarly shaped and coloured species. See Bernard Picton's message for further pictures of this animal.
Best wishes,
Bill Rudman

Thanks Bernard,
Bill Rudman

Thanks Stuart,
Bill Rudman

Dear Mary,
Have a look at my reply to Alexandra's message. This is a 'form' of Hypselodoris bullocki which is a specialist sponge feeder. All nudibranchs are carnivorous. The "lettuce" nudibranch your supplier mentioned is Elysia crispata and is a herbivore. However it is not a nudibranch, but a related group of opisthobranchs or sea slugs, which are known as sacoglossans.

As you will see from previous messages, aquarium suppliers are not a good source of accurate information on sea slugs.
Best wishes,
Bill Rudman

Dear Nick,
While egg-laying can be a result of stress, mating is just something they do when they come into contact with each other. It is possible they, or one of them, will lay fertile eggs, but without food they may not be able to produce sufficent yolk or the protein needed for the egg capsules. Even if viable eggs are produced it is unlikely that the planktonic veliger larvae will survive as they will need particular planktonic unicellular algae (phytoplankton) to feed on until they are ready to metamorphose into a bottom dwelling slug. The larvae also need some chemical trigger, usually provided by their adult food sponge, to cause them to settle out of the plankton and change into a crawling slug. Basically I can't offer any words of hope - either for the adults, or for any potential second generation.
Best wishes,
Bill Rudman

Dear Matt,
Have a look at Mike Miller's message for a good photo of its egg mass. You'll see the eggs appear as tiny yellow spots to the naked eye. Your description of a 'yellow cloud' does suggest your animal is in trouble. Often when nudibranchs are stressed they lay, or attempt to lay eggs. If they have mated and have fertile eggs they can quite often lay a normal egg ribbon in which the larvae develop quite healthily. However if they are very stressed, or have never mated, then they can go through 'the motions' of laying an egg, but instead of laying eggs in individual capsules, each with a portion of yolk, they just extrude quantities of yellow yolk into a mucous ribbon. It looks like that is what your animal has done.

All the 'egg ribbon' will be good for is fish food. Nudibranchs are all hermaphrodites, each with a full functioning male and female reproductive system. In Mary Jane Adams's photo you can see a pair of H. bullocki mating. In most nudibranchs, mating consists of an exchange of sperm between the partners.

Best wishes,
Bill Rudman

Dear Mary Jane,
What a wonderful find! I am not sure that all the colour 'forms' I have accumulated on the Hypselodoris bullocki pages are in fact one species, but I have been pretty sure that some of them are. Your photo of these two colour forms mating is pretty convincing evidence that these two are the same species.

I don't know how else to say that this is an important discovery - just as important as finding a new anatomical character. So please, anyone out there with interesting photos of animals eating, laying eggs, or mating - especially if the pair are badly matched in colour, please send them in.
Best wishes,
Bill Rudman

Dear Drew,
If you read some of the other messages about H. bullocki in aquaria you will see that your animal is probably not very healthy. Certainly it normally lays a spiral egg ribbon - and there are a number of photos in previous messages. Often nudibranchs lay their egg ribbons in a straight or irregular way when they are stressed. Its biggest problem is the lack of food. Your coral is quite safe as H. bullocki is a sponge feeder, but unfortunately not any sponge will do. It will only eat one or a few related sponges from its native habitat - and unfortunately we don't know which species of sponge they are. And although your live fish dealer will say they are plant eaters, he is wrong, and sadly he won't have the sponge your animals needs either.

The umbrella shaped things on its back are its gills. I am sure if your fish are happy then there is enough oxygen in the tank for the nudibranch. Some nudibranchs seem to prefer moving water, perhaps its because the sponges they eat need currents to live healthily.

Best wishes,
Bill Rudman

Dear Alexandra,
I checked out Aquacon's website and as you say they have an illustrated advertisement for:
REEF SAFE PURPLE NUDIBRANCHS W/ YELLOW ANTENNA'S !
Add bright color to your tank and take care of algae at the same time! If you have nasty green algae on your rocks and/or glass these clean up guys will move along and help you with your tank in a hurry. (2 - 3") $15.00 ea. / 3 for $40.00 GREAT FOR BEGINNER'S

This is of course quite incorrect. Your purple slug is what I am calling Hypselodoris bullocki. There are now three pages of messages concerning this species on the Forum, many of them from aquarium keepers wanting to know how to feed them. The short answer is that anyone who tells you they eat green algae either doesn't know what they are talking about or is trying to trick you. In either case I think you should complain. As you will see in earlier messages Hypselodoris bullocki is a carnivore, feeding on sponges. Unfortunately we do not know which species of sponge it eats, but I would suspect that like related species it will only feed on one or two partcular species. Your supplier obviously dowsn't know what species they feed on so he won't be able to supply it for you. The other major problem is that even if you knew which sponge to feed it, keeping sponges alive in aquaria is difficult. And keeping sponges alive, while they are being eaten is even more difficult.

Concerning the egg ribbon. Yes it will be your slugs. I'm afraid egg-laying is not a sign of well-being, in fact it is often a sign of stress.

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

Dear Sammy,
As you will see from other messages on the Forum, these fish shops have no right to say they know how to feed nudibranchs when clearly they don't. I'm afraid that even if we knew which species of sponge your animal ate, there is little chance of getting it for your aquarium.. Even if by some miracle you got the sponge, keeping it alive while it was being slowly eaten by your nudibranch, would be almost impossible.

I'm sorry I can't give you good news. The only thing I can advise you to do is go back to the LFS that sold you the Hypselodoris and tell them what you think of their spurious advice.
Best wishes,
Bill Rudman

Dear Drew,
These are definitely an interesting group of animals. I find it interesting that most amateurs with more than a passing interest in nudibranchs, feel as I do, that all these 'colour forms' are somehow related, despite the fairly distinct differences in colour pattern.

Any further help with 'biological clues' such as egg masses, sponge feeding etc, is always welcome.
Best wishes,
Bill Rudman