Dear Zeineb,

Thanks for these photos. They help to illustrate the difficulties in distinguishing species of this genus as the pair in your second photo are almost certainly what I would call Mexichromis mariei. The tubercles in that species are more rounded and spaced than in M. multituberculata.

Clearly this genus needs some more work

Best wishes,
Bill Rudman

Dear Valda,

Yes I would call this M. multituberculata. The orange mantle border is more  complete than we usually see but I assume it's just part of the variability. This is the furthest south in the Indian Ocean I think it has been found, but since we have records from Reunion Id I guess it was only a matter of time.

Best wishes,
Bill Rudman

Dear Darja,
The pointed tubercles on the mantle are similar to those of some Cadlinella, but this is a species of Mexichromis, and almost certainly the one we are calling Mexichromis multituberculata. However the more photos I see of this 'species' the more I wonder whether there is one variable species ranging in colour from purple to reddish spots and ranging in the degree the spots became raised into rounded tubercles and even pointed tubercles. When I first tried to identify a specimen of this purple spotted form [from India - Rudman, 1973] I concluded it was a form of C. mariei (Crosse, 1872) first described from New Caledonia. Until recently I have been happy to accept Baba's name M. multituberculata for animals with large pointed tubercles on the mantle, but the variability shown in photos on the Forum which I have variously identified as M. mariei, M. cf. mariei. M. multituberculata and M. cf. multituberculata make me wonder if they are all variations of one species. Even M. festiva and M. macropus are very similar [see Rudman, 1983].

If this form with pointed tubercles is considered distinct the Chromodoris sannio Bergh, 1890 is a much earlier name. It was described from Indonesia and the purple spots were described as being raised on vesicles. Charles Eliot (1905) reported similar animals from Muscat 100 years ago and identified them as C. sannio. So what should you call your animals? I would suggest you use Mexichromis multituberculata, but I suspect when this group is sorted out we will use M. mariei for them all, or perhaps M. sannio for the pointed ones.

If this species is quite common in your area, it would be worthwhile keeping a lookout for variability in colour and whether the spots vary from rounded tubercles to pointed papillae. If we are dealing with a variable species it would be nice to get some evidence of it in local populations.

• Bergh, L. S. R. (1890) Die Nudibranchien des "Sunda-Meeres". Malacologische Untersuchungen. In: C.G. Semper, Reisen im Archipel der Philippinen, Wissenschaftliche Resultate., 17, 873-992,Pls.885-889.
• Crosse, J. C. H. (1872) Description d'un genre nouveau et d'espèces inédite, provenant de la Nouvelle-Calédonie. Journal de Conchyliologie, 20, 148-154.
• Eliot, C. N. E. (1905) Nudibranchs from the Indo-Pacific. 1. Notes on a collection dredged near Karachi and Maskat. Journal of Conchology, 11, 237-256.
• Rudman, W. B. (1973) Chromodorid opisthobranch Mollusca from the Indo-West Pacific. Zoological Journal of the Linnean Society, 52, 175-199,177figs,172col.pl.
• Rudman, W. B. (1983) The Chromodorididae (Opisthobranchia: Mollusca) of the Indo-West Pacific: Chromodoris splendida, C. aspersa and Hypselodoris placida colour groups. Zoological Journal of the Linnean Society, 78, 105-173.

Best wishes,
Bill Rudman

Dear Mike,
This is the very exception to the one species per message rule which I welcome - the mixture of species is the topic. I am not sure what the red stuff is all through the background of your photo but I suspect it is a cnidarian [sea anemone or soft coral]. The sponge they are all eating - or at least associated with - is a blue species of Dysidea. We have records of all three species feeding on this blue Dysidea but this is a nice illustration of my hypothesis that food is probably a, if not the, major cause of these inter- and intra- species aggregations.

Best wishes,
Bill Rudman

Dear Richard,
Yes this is Euryspongia. At this stage, our understanding of feeding specialisation in these animals is in its infancy, so all new records are welcome. This is one of those sponges which can apparently withstand a layer of silt over much of the colony - at least for short periods.  I suspect all the brownish background in your photos are part of the sponge colony.

Best wishes,
Bill Rudman

Dear Ken,
Firstly I see you would like clarification on the identification of Mexichromis multituberculata - wouldn't we all! I foolishly thought I had them sorted out many years ago (Rudman, 1973, 1983, 1984) but as more material comes available, colour and shape of the tubercles seems to become less important in this group of species. It is a very instructive lesson in showing that we have much to learn. Many colour picture books / identification guides tend to give the impression we know it all  but that is far from so. All I can say at present is that your animals seem to be part of the colour variability of M. multituberculata - but its possible there is an earlier name available.

You didn't mention the sponge you animals are on. This is a species of  Euryspongia, which seems to be the food choice of this species. From the yellow spots on the dorsum and the red on the gills, I suspect the little juvenile is Hypselodoris infucata. It is normally found feeding on dysideid sponges, so it wouldn't be out of place on Euryspongia.

• Rudman, W.B. (1973) Chromodorid opisthobranch Mollusca from the Indo-West Pacific. Zoological Journal of the Linnean Society, 52(3): 175-199, 7 figs, 2 col. pl.
•  Rudman, W.B. (1983) The Chromodorididae (Opisthobranchia: Mollusca) of the Indo-West Pacific: Chromodoris splendida, C. aspersa and Hypselodoris placida colour groups. Zoological Journal of the Linnean Society, 78: 105-173.
• Rudman, W.B. (1984) The Chromodorididae (Opisthobranchia: Mollusca) of the Indo-West Pacific: a review of the genera. Zoological Journal of the Linnean Society, 81: 115-273.

Best wishes,
Bill Rudman

Thanks Jim,
This is a good example of what I would call the 'typical' colour form of this species. As I discussed in Philibert's recent message [#18462], there seems to be considerable colour variation in this species
Bill Rudman

Dear Philibert,

As you will see in earlier messages [#8655], my feeling is that Mexichromis multituberculata encompasses colour forms with orange and wine red mantle borders as well as the typical blue border. Nathalie Yonow's Mexichromis katalexis, with orange spots around the mantle border and wine red-tipped tubercles would seem to be part of the colour variation within this species. Yonow (2001) considers there are radular differences - the first two laterals are not as flattened as the other laterals - but she only had glass slide mounts of the radula so such differences could be as much to do with the thickness of the mounting medium as any real morphological difference.

We now have a lot of photos on the Forum showing colour variability in this group of the genus. I don't think there is much to be gained in pulling out one colour form and giving it a new species name. Your animal shows the problems in thinking that way. If we accept M. katalexis with red tipped tubercles and orange-yellow patches around the mantle border, we would have to make a new species for your animal with blue-tipped tubercles and an almost continuous yellow line around the edge of the border, and another for the form with red tips and red border etc, etc.

• Yonow, N. (2001) Results of the Rumphius Biohistorical Expedition to Ambon (1990). Part 11. Doridacea of the families Chromodorididae and Hexabranchidae (Mollusca, Gastropoda, Opisthobranchia, Nudibranchia), including additional Moluccan material. Zoologische Mededelingen uitgegeven Rijks Museum van Natuurlijke Historie te Leiden 75: 1-50.

Best wishes,
Bill Rudman

Dear Lawrence,
This is Mexichromis multituberculata.

Best wishes,
Bill Rudman

Dear Martina,
From the very large tubercles this can only be Mexichromis multituberculata, which makes your find a very large range extension from the Western Pacific.

One thing of special interest is that your photos could have been part of the same series of photos in Jun Imamoto's message [#14106 ] from Japan. In both cases, the animals are feeding on the same sponge, which Dr P.R. Bergquist has identified as a species of Euryspongia [F. Dysideidae]. This is a very valuable addition to our knowledge of the biology of this species.
Best wishes,
Bill Rudman

Thanks Jun,

We have very little information concerning any species of Mexichromis feeding, so this is a valuable addition.

Best wishes,
Bill Rudman

Thanks Mary Jane,
I see that in Stuart Hutchison's message I had decided that Mexichromis multituberculata almost certainly included animals with red, purple, blue or orange spots around the mantle edge. So I have finally plucked up the courage to amalgamate the animals on the Mexichromis cf. multituberculata with those on the Mexichromis multituberculata Page.
Best wishes,
Bill Rudman

Thanks Stuart,
I think we are only on step away from demonstrating that Mexichromis multituberculata can have either blue or orange spots around the mantle edge. And if we include Mike Miller's earlier photos, we can include a wine-red colour in the variation as well.

What would be nice is a photo of a blue-spotted form mating with an orange-spotted animal. I am just about to go off for a week's fieldwork but when I return I think I will either combine these animals with the M. multituberculata Page or at least make a strong suggestion on that page that they are probably all the same species.
Best wishes,
Bill Rudman

Dear Mika,
This is a species of Mexichromis. At present it is not quite clear how many species there are and just how much variation there is in colour and pointed tubercles within each species. So at the moment, until more reserach is completed on the group, I am calling animals that look like yours Mexichromis cf. mutituberculata. The 'cf' just means that it looks quite like Mexichromis multituberculata but is probably something else.

If you look at the top of this page you will find links to other similar species of Mexichromis
Best wishes,
Bill Rudman

Thanks Mike,
This looks very interesting. Although its hard to be sure, the eggs look quite big - and as you can see in my photo they are at least as big as the eggs of Mexichromis festiva, which is a direct developer. Your animal's eggs are also the same colour, but the wavy edge is different. It would certainly be good to see some egg masses from the other species of Mexichromis.
Best wishes,
Bill Rudman

Dear Mary Jane,
I am afraid there is no simple answer at present. If you read some of my comments on the Mexichromis pages you will see that my 'simple solution' has been scuttled by an embarassment of specimens. I am just arranging photos in 'look alike' groups until I can rework the material I have in hand.

So I have put your animals on the Mexichromis cf. multituberculata page, but at present the limits are blurred and it seems that the degree of tuberculation may not be a useful species character, more than one species may in fact have a range from low rounded tubercles to quite elongate pointed papillae.

Best wishes,
Bill Rudman.

Dear Michael,
Your picture is very interesting. I have looked at specimens from eastern Australia and New Caledonia which are identical to the animal with the orange-spotted border, but I have never seen the form with the wine-red spots which is clearly conspecific. I have had difficulty making sense of the complex in the southwest Pacific but your find may be very useful. One possibility is that this "species" may in fact be a distinct species mimicking M. multituberculata in the north and M. mariei in the south.
Bill Rudman.