Dear Patty,

Action photos are always welcome and it does not matter if we already have photos of the same animal feeding. In fact it is best we have multiple observations because then we can be more confident that the food item is a normal part of the diet rather than a strange one-off activity.

Concerning the species. The upper one is certainly C. willani, but the lower one is Chromdoris annae. There are a number of similarly coloured species but one sure way to identify C. annae are the small dark specks all over the bluish parts of the mantle, which can be seen in the close-up alongside. Also in the close-up we can see a large cavity in the sponge just above the slug, which certainly looks like feeding damage.

This dark grey sponge is almost certainly a species of Petrosaspongia, which both species have been reported on before [see messages #12039; #12040; #12005; #16257]. Your photo then is valuable confirmation of the food choice of these two species. Finding two similarly coloured species together on the same food sponge is also interesting because it suggests why there are these groups of similarly coloured species. I have described a group of red-spotted species on a separate page and explain how I think that these groups of similarly coloured species living in close geographic proximity have evolved to warn predators to leave that colour pattern alone. I suspect that these more widely spread black-lined species also 'teach' predators to leave their colour pattern alone by grouping together on the same food sponges. In this way all the black-lined species would share the load of 'teaching' predators that black-lined slugs contain extremly distasteful chemicals and aren't worth biting.

Best wishes,
Bill Rudman

Dear Marcel,

Thanks again for checking out feeding records and in particular, red and white sponges. It would have been nice to have C. willani on a red sponge, like we have found the similarly coloured C. quadricolor and C. hamiltoni but in this case the red is not a sponge pigmentation but a coloured layer on the surface of the grey sponge. In your upper photo it is restricted to the ridges while in the lower photo it seems to form a uniform layer. Sponges quite often incorporate other organisms in the outer layers and I suspect this is some plant or bacterial layer. The sponge is almost certainly a species of the thorectid genus Semitaspongia, either the same or related to the sponge in your earlier message [#22170]. As I commented in that message, I am very grateful for any sponge association photos, because getting the same result many times is a valuable confirmation of its food choice.

Your photos also show the dark and paler colour forms together. I has wondered if this was a result of different food sponges but that doesn't seem likely from your photos. Also of interest is the brown submarginal band around the mantle. I have had great difficulty seeing the mantle glands in this colour group of chromodorids. Usually in species of Chromodoris they are easy to see as opaque white bands or ramifying clusters, but in this group there is usually no sign of them. The brown of this band closely matches the brownish colour of the sponge. Perhaps this is the place the antifeedant molecules from the sponge are accumulated in these species. If they are in sacs or glands we will need to look harder for them.

A very interesting message
Best wishes,
Bill Rudman

Dear Marcel,

At present we have records of this species feeding on thorectid sponges of the genera Semitaspongia and Petrosaspongia. I am pretty sure the sponges they are feeding on in these photos is a species of Semitaspongia. I have labelled a couple of areas in your upper photo and include close-ups of them. Area A looks like their potential food but I suspect it is an ascidian colony, or if a sponge it is the wrong superfamily. There is no sign of feeding damage on that colony. On the rock below A there are many traces of a greyish sponge [B] which I am sure is what the chromodorids have been eating. it certainly fits with the sponge in the middle right photo which is a thorectid. The sponge in the lower photo does not show a lot of detail but from many other photos I have seen, I am pretty sure it is also a half-eaten colony of Semitaspongia.

Thanks for looking for white sponges. Although 'whitish' these are not the same as the few sponges which can be described as 'white' not because they are a 'wishy washy' translucent colour, but because they are pigmented white or 'off white'. Whether they are white or not I am very happy to get them as they help us to build up a more complete picture of what this species chooses to eat.

Best wishes,
Bill Rudman

Dear Su,

Thanks for the message. In fact the animal in your lower photo is not a 'typical' C. willani but Chromodoris lochi. It is very similar in colour to C. willani, but the most obvious difference is that the gills lack the white spots so typical of C. willani. It is not unusual to find the two species together, or nearby, as they seem to feed on the same species of sponges. In your upper photos [of C. willani] both the dark brownish sponge which the animal is sitting on, and the grey sponge just above, are both potential food sponges for this species.

Best wishes,
Bill Rudman

Dear Su,

I am pretty sure this is a colour form of Chromodoris willani. It has more black lines than usual, but the white spots on the gills and rhinophores are characteristic of that species. In an earlier message I discusss the differences between one of the colour forms of C. dianae and C. willani [#19469].

If you have a photo showing the dark grey sponge it appears to be eating I would be interested

Best wishes,
Bill Rudman

Dear Jeffrey,
I am not sure if the strange muation you are referring to is the colour of the animal or the strange disc-like or cone-shaped object in front of the gills. We have a number of records of similar strange growths in chromodorids on the Abnormalities list including one on C. willani [see message #20241 ].

Concerning the colour pattern, the body looks like C. dianae but the gills and rhinophores are characteristic of C. willani. I suspect it is a strange C. willani but that is just a guess.

Best wishes,
Bill Rudman

Dear Barbara,

If you get a chance to follow this up I would be interested to know what you find. Certainly C. willani has a more oval shaped mantle with a wider 'skirt' than C. lochi, but spots, or lack of spots, on the gills and rhinophores may be more difficult to see in situ through a mask.

C. willani  has also been found together with C. elisabethina on another thorectid sponge Luffariella sp. [message #12031] which lends support to the suggestion that these species, which look alike, are part of an aposematic mimicry group in which distasteful species with similar colour patterns share the load of teaching fish to leave them alone.

Best wishes,
Bill Rudman

Dear Barbara,

I am very glad you did send these photos. It's true I can't positively identify the sponge but I am pretty sure it is Semitaspongia again, which is useful in building up a full picture of its feeding behaviour.

Another very interesting thing is the apparent lack of white spots on the gills and rhinophores. By fiddling with the image files I was able to enlarge the gills in the upper photo to show there are white spots on the gills in that animal. . However I can find no sign of white spots in the animal in the lower photo or in the one laying eggs. At first I thought this was a sign that C. willani might sometimes lack white spots on the gills and rhinophores, but on reflection I suspect the animal in the lower two photos is C. lochi, which feeds on the same sponges as C. willani, but lacks white spots on the gills and rhinophores and has a more elongate mantle with a much narrower 'skirt' or overlap.

Which means the photo of the animal with the flat-egg ribbon is either a useful addition to Mike Krampf's photo [message #20399] of C. willani laying a flat egg ribbon or is the first photo I have seen of C. lochi and its similar egg ribbon. Either way it gives me a chance to nnote the very similar biology between these two very similar looking species.

Best wishes,
Bill Rudman

Thanks Gary,
Yes there have been quite a few messages about C. willani recently - must have a new publicity agent!

Best wishes,
Bill Rudman

Dear Mike,
They are indeed interesting. It has become important to know what type of egg mass each species of Chromodoris is producing because Nerida Wilson's work is suggesting that those which lay a flat egg ribbon form a separate branch within the chromodorids distinct from other species we at present call Chromodoris. This is supported by recently published work on their feeding (Rudman & Bergquist, 2007) which shows that this flat egg group feed on quite different sponges from the rest of the species of Chromodoris. All we know about the egg ribbon of Chromodoris willani is from Nick Gill's message #5711. While I have no reason not to believe him, it is always more satisfying to have an illustration to confirm the identification. I must say this animal is making a bit of a mess laying the ribbon but it certainly seems to be a flat ribbon,

• Rudman, W.B. & Bergquist, P.R. (2007) A Review of feeding specificity in the sponge-feeding Chromodorididae (Nudibranchia: Mollusca). Molluscan Research, 27: 60-88
• Wilson, N. G. (2002). Egg masses of chromodorid nudibranchs (Mollusca: Gastropoda: Opisthobranchia). Malacologia, 44(2): 289-305
• Wilson, N. G. and Lee, M. S. Y. (2005) Molecular phylogeny of Chromodoris (Mollusca, Nudibranchia) and the identification of a planar spawning clade. Molecular Phylogenetics and Evolution 36: 722-727.

Best wishes,
Bill Rudman

Dear Ken,
Yes this is C. willani. Its important to see the whole pattern [what German philosophers would call the gestalt] when identifying nudibranchs. Its not the individual parts of a pattern - that is three lines - we need to see, but the whole pattern. For evolution to work we must have variability, so we should expect a broken line or an extra spot now and then. There are usually a few key characters - like white spots on the gills and rhinophores in C. willani - which are important, but most other aspects can be expected to show some variation. How much variation? ... who knows? ... that is why we still have to keep looking and only half believe what we read.

Best wishes,
Bill Rudman

Dear Ken,

You are partly right. The two on the left are C. willani but the one on the right is almost certainly C. lochi. Its rhinophores have a pinkish orange tinge and no sign of spots. Certainly seeing three animals together like this makes you think its all one species, but both these species feed on the same sponges so its possible that food has brought them together. If you look at the top left of your photo there is a greyish patch [see close-up in bottom photo] which could well be their food sponge.

Best wishes,
Bill Rudman

Dear Carlos,

Firstly, this is C. willani - the white spots in the single rhinophore are chracteristic of the species. The single rhinophore however is abnormal, as its apparent replacement by a cone-shaped growth. We have a similar abnormality in a specimen of C. kuniei [#9918].

This is the second species you have sent today [see message #20212] which belongs on the abnormalities page - I hope these are very rare occurrences in your area.

Best wishes,
Bill Rudman

Dear Mike,
Thanks for thinking of me. Yes I welcome photos of sea slugs 'doing things'. We still have a lot to learn about almost every species. Your photos certainly illustrate some of the difficulties we have in building up this type of information. The dark grey lumps are almost certainly the sponge food of these animals, but there is nothing very clear about them to positively identify them. I suspect they are a species of Semitaspongia on which this species feeds, the only clue apart from colour, are the raised bits all over the colony which could be fibre bundles as illustrated in an earlier message [message #16270 ].

Best wishes,
Bill Rudman

Dear Guido & Philippe,
This is the third message [see #16257, #16270] dealing with your photos of C. willani which I have used to illustrate some of the [problems with building up feeding information on sponge-feeding dorids. In this message I have included examples of two extremes of body sahpe ina species of Semitaspongia which I discussed in the last message [#16270], the upper one is smooth with large oscules [siphons], and the lower one has very prominent bundles of fibres - which form the sole skeletal material in these sponges - protruding from the surface of the sponge body.

The upper sponge also shows how large sponge colonies can become overgrown with all sorts of plant and animal growths so that sometimes, as illustrated in message 1 [#16257], it is difficult to know there is a sponge present. That is why in many photos on the Forum, where there is an aggregation of one species of chromodorid, I am pretty sure there is a sponge underlying the growths we can see in the photo. Unfortunately it doesn't help to identify which sponge they are eating.

Thanks Guido & Philippe for this very educational group of photos.
Best wishes,
Bill Rudman

Dear Guido & Philippe,
I have included close-ups of three parts of the sponge colony shown in your upper photo to show how the external structure of sponges can vary considerably. [see messages #16257, #16271 for further photos of C. willani feeding].

This photo illustrates another point concerning building up information on nudibranchs feeding on sponges. Once you are sure that you have a feeding observation you have to be abe to identify the sponge. While a few species are instantly recognisable, many sponges can only be identified by studying tbeir microscopic structure. External structure can often be misleading, as many sponges grow quite different shapes in different environments. This colony of Semitaspongia is an excellent example, because it has three quite distinct growth forms in one colony: a honeycomb pattern of radiating ridges, a pattern of exposed raised bundles of fibres, and a smooth area with large oscules. In the other two messages I have include examples of sponge colonies of the same species which have only one of these growth forms.

Best wishes,
Bill Rudman

Dear Guido & Philippe,
Thanks for these photos. When I found your wonderful website I found these interesting feeding photos of chromodorids which I am so glad you have allowed me to share with visitors to the Forum. There are two more messages with further photos of C. willani feeding as they help to illustrate the difficulties in building up information on feeding in these animals. [see also message #16270, #16271.

One of the biggest problems when finding a nudibranch on a potential food item is judging whether it is just crawling over the item or is in fact feeding, about to feed, or just finished feeding. If you just have photos, a closer look is not possible, but if you are taking the photos then it always pays to gently 'nudge' the animal and see if it has its feeding apparatus extended, or if its head is near, or in, a suspicious hole in the food item. Another good sign is if you find a cluster of animals all on one object. In the upper photo we can see a cluster of C. willani all on some algal or bryozoan-encrusted object. Whenever you see an aggregation like this it is worth having a closer look. As I will show you in the other messages this is in fact a large colony of the sponge Semitaspongia. The lower photo is a close-up from another locality of an animal on a sponge which shows clear signs of being eaten - see the rough patches in front of the slug. I am pretty sure it is a related sponge, Petrosaspongia.

Best wishes,
Bill Rudman

Dear Asther,
This photo shows the small scattered whitish dermal glands that this group of chromodorids have on their mantle. They are secondary to the deeply embedded mantle glands which are hard to see in these species with opaque mantles.
Best wishes,
Bill Rudman

Thanks Asther,
Your photos show the characteristic white spots on the gills very clearly.
Best wishes,
Bill Rudman

Dear Asther,
Thanks very much for this observation. Getting information on the biology of these animals is not always easy. Obviously actually catching them feeding with their oral tube everted, or with their head in a freshly excavated hole, are the ideals, a good second best is to build up information on regular associations with a particular food. Even though you have not actually witnessed feeding, your observations fit a number of other observations on the Forum of a close association between C. willani and this sponge.
Best wishes,
Bill Rudman

Dear Roberto,
This certainly looks like the sponge in your earlier message. It's good to get repeat sightings of these species on the same sponge. Even if we can't see actual evidence of feeding, the regular occurrence of a species on a particular sponge is pretty good evidence of a biological association
Best wishes
Bill Rudman

Dear Roberto,
Thanks for this photo. I have just been discussing your 2 sponges with a sponge expert, and her tentative opinion is that they are two closely related species. As soon as I have some names for these sponges I will let you know. In the mean time, more photos of chromodorids on these sponges, or for that matter chromodorids on any sponges would be valuable
Best wishes
Bill Rudman

Thanks Roberto,
This is the first evidence we have of its food
Bill Rudman

Dear Andy,
All things being equal, I would say the first thing to consider is its food. As you probably know, most nudibranchs have a very specific diet, and in the case of chromodorids this means each species usually eats only one or a very few species of sponge. Therefore the most important factor affecting where it lives will be its food. I guess its a bit late now but my advice would have been to identify its food sponges and find if their local distribution and that of C. willani coincided. The other important factor to look at when considering local distribution of a species is its development type. If the species lays eggs which develop into planktonic larvae then there is probably not much relationship between adults and their off-spring. However if the species has direct development and the young hatch out of the eggs capsule as a crawling young then there would be a clear relationship between the presence of adults and the presence of young. So the second bit of advice I would have suggested would be to look at the type of development found in C. willani.
Best wishes,
Bill Rudman

Dear Asther
This nice shot is of Chromodoris willani. It an be identified by the white spots on the translucent gills and rhinophores.
Best wishes,
Bill Rudman

Thanks Helmut,
This is Chromodoris willani.
Bill Rudman

Thanks Nick,
This is an interesting observation as I don't think we have a record of the egg mass of C. willani. By coincidence, Scott Johnson is discussing these flat egg masses in a separate message today. Chromdoris willani certainly fits in the colour group of chromodorids which are reported to have a flat egg mass.
Best wishes,
Bill Rudman

Dear Nick,
I'm sorry you can't provide a photo because this may be the first observation of its egg ribbon. Firstly, are you sure of your identification of the slug as C. willani. One way to check its not the similar looking Chromodoris lochi is to see if it has white spots on the gills and rhinophores [see photos at top of this page]. Secondly, when you describe the egg ribbon as 'lying flat' are you describing an egg ribbon like the ones on the 'flat egg-ribbon' page rather than the more typical egg ribbon which is flattened but attached along one edge [see Mike Miller's photo].

Now the bad news. Nudibranchs under stress often start laying eggs. It is nice to think that this is nature's way of helping the species survive but it is equally likely that as the body's equilibrium begins to break down strange things happen. Sometimes the eggs seem to be produced intact and fertilised but often the 'egg ribbon' has no eggs in it, and sometimes the yolk is there as long thin smears or ribbons. I suspect your slug is telling you it is not very happy. I would be grateful for some feedback on the questions I have asked about the egg ribbon and the slug's identity.

Best wishes,
Bill Rudman

Thanks Mary Jane,
Your trip to the Philippines was obviously very rewarding.
Best wishes,
Bill Rudman

Dear Paulo,
I agree that shops shouldn't be selling live animals that customers haven't got a reasonable chance of keeping alive. There have been quite a few queries to the Forum abut this topic. Have a look at the recent message about Hypselodoris bullocki for some more information on the topic.

Most chromodorids have a very specialised diet, each species having its own special choice of one or a few species of sponge. in general, they feed on sponges which do not have siliceous spicules, instead having a skeleton of spongin fibres. I don't know what species C. willani feeds on naturally but as it will not occur in Brasilian waters what you need is a Brasilian species that it may eat. If you live near the sea perhaps you could try a few local sponges. On problem of course is that sponges are not that easy to keep alive in aquaria.

If you have some way of identifying your local sponges, perhaps you could try species in the following families and genera which are recorded as food for various chromodorid species.

ORDER Dictyoceratida
• Family Spongiidae - Spongia
• Family Thorectidae - Psammocinia, Ircinia, Fasciospongia, Hyrtios
• Family Dysideidae - Dysidea

ORDER Dendroceratida
• Family Darwinellidae - Aplysilla, Darwinella, Chelonaplysilla, Dendrilla

ORDER Haplosclerida
• Family Callyspongidae - Callyspongia, Chalinopsilla.

I can't guarantee you will have any success but when I was a student in New Zealand, a friend was studying the feeding preferences of the dorid nudibranch Rostanga muscula, which is only found in New Zealand. It turned out that its most preferred food was a sponge which had been accidently introduced into New Zealand from Europe, only 2 or 3 years before. So 'foreign' sponges can be eaten at least by some dorids.

Anyway at this stage anything is worth a try.
Best wishes,
Bill Rudman.

Dear Magenta,
This is Chromodoris willani, another southwestern Pacific species. It is easily recognised by the white spots on the gills and rhinophores.
Best wishes,
Bill Rudman.

Dear Lindsay,
It is C.willani. The important point is the white spots on the gills and rhinophores. The background colour of the rhinophores tends to vary in this and some other species including the similarly coloured C. lochi. ... Bill Rudman.