Thanks Deb,

It's nice to get photos of any of these species laying eggs. There are a group of species of the related genus Tambja [see T. affinis colour group] with a similar colour pattern to your Roboastra, but most of them lack the type of oral tentacle we can see in one of your photos. Fortunately the one species of Tambja with this type of oral tentacle, Tambja tentaculata, has a distinctively different colour pattern.

I have also included a close-up to show how the yellow lines on the body are really folds into which glands embedded in the skin have their opening. When these animals are disturbed they can exude a thick viscous white or yellow secretion to deter potential predators.

Best wishes,
Bill Rudman

Dear Graham,
Hopefully someone will get in touch with you

Best wishes,
Bill Rudman

Dear Graham,
This is a very interesting observation. There haven't been many studies on species of  Roboastra, but the few that exist are focussed on the feeding behaviour of the predator - what prey does it choose, how does it sense its prey and how does it attack and eat it. These predators can certainly identify their prey from the mucous trail they leave. Megina & Cervera (2003) on their report on Roboastra europaea mention that one of its prey items, Tambja ceutae, has a spectacular defensive response when it touched a Roboastra or was touched by one. It would immediately and vigorously begin undulating its body and swim away. From your description Tambja morosa can identify some chemical in the mucous trail of R. luteolineata as a warning of immediate danger, and so elicit the same escape response.  I can't say whether the animal you observed has learnt to do that from past experience or whether it is an instinctive reaction.

It definitely a research project for a student who wants to escape to warm waters for a while.

• Megina, C. and Cervera, J. L. (2003) Diet, prey selection, and cannibalism in the hunter opisthobranch Roboastra europaea. Journal of the marine biological Association, U.K. 83: 489-495

Best wishes,
Bill Rudman

Dear Graham,
Thanks for the interesting sequence of photos. The fortunate 'prey' animal is very similar to a photo I have identified as Tambja tentaculata [message #14883]. We don't know much about that recently named species, but if it is like other species of Tambja, it will feed on bryozoans. Chromodoris willani is quite different in shape and colour, and is a sponge feeder.

Nudibranchs of the genus Roboastra are well-known as hunters, but it seems they restrict their prey to other nudibranchs of the family Polyceridae. They certainly seem to eat smaller members of their own species, so I guess you can call them cannibals, but they are not exclusively cannibals. The two species most studied are the tropical American R. tigris which feeds on Tambja abdere and T. eliora, and the European R. europaea, which feeds on a variety of polycerids (Megina & Cervera, 2003). From work on R. tigris, we know that distasteful chemicals are incorporated in tissues of the bryozoan-feeding species of Tambja, and then transferred to the Roboastra, when it eats them (Carte & Faulkner, 1986). I presume something similar could happen with Tambja tentaculata and R. luteolineata, but I doubt it would lead to the Roboastra rejecting the Tambja. It is possible the Roboastra was just being greedy. These hunters seem to attack by reflex action whenever they come across prey. Perhaps it discovered it didn't really have room inside once it started swallowing.

• Carte, B. & Faulkner, D.J. (1986)  Role of secondary metabolites in feeding associations between a predatory nudibranch, two grazing nudibranchs, and a bryozoan. Journal of Chemical Ecology, 12(3): 795-804.
• Megina, C. and Cervera, J. L. (2003) Diet, prey selection, and cannibalism in the hunter opisthobranch Roboastra europaea. Journal of the marine biological Association, U.K. 83: 489-495.

Best wishes,
Bill Rudman

Dear Kristin,
The feeding behaviour is enough to separate the Roboastra from a bryozoan feeding Tambja. This is a nice observation as it is only the third record we have of this species feeding - all three observations being recorded on the Forum. Nembrotha morosa, Tamba verconis, and now N. kubaryana.

Concerning the reproductive organs protruding. I suspect this is to do with the nature of the body rather than any misplaced hormones. These animals have no hard skeleton so their shape is totally dependent on muscles working against their hydroskeleton. They are in fact a bag of watery blood. If you think of a rubber glove with its fingers popped inside out. If you fill the glove with water one or more of the fingers is going to pop out when the pressure increases enough. You can see that the Roboastra has pushes all its fluid to the front half of the body, presumably to help push out the buccal bulb so it can engulf the Nembrotha. I suspect the partial eversion of the reproductive organs is result of the greatly increased pressure in that part of the body. I am not sure why Nembrotha has also partially everted these organs, but I guess quite a lot of cross-wires are occurring in its little brain as it fights for its life.
Best wishes,
Bill Rudman

Dear Pat,
Yes this is Roboastra luteolineolata. The long oral tentacles on either side of the [bluish] mouth are typical of species of Tambja, although there are a few species of Tambja [see Tambja tentaculata] which break the rule..
Best wishes,
Bill Rudman

Dear Bieke,
I would be interested to know where the video you looked at was taken? Was it in New Zealand? We know so little about the feeding behaviour of these animals that every record is important. Concerning the 'smoke' you noticed. Species of Tambja, Nembrotha and Roboastra have special skin glands which at times exude coloured secretions. These are probably defensive and appear to contain antifeedant chemicals from their prey, which in the case of Tambja would be an arborescent bryozoan.

How do they digest such large prey? I'm afraid carnivorous molluscs are not very very well mannered when it comes to eating. An animal such as your Roboastra will just have to sit for many hours hugely distended until its digestive enzymes dissolve its prey. I have commonly seen the worm-eating slug Melanochlamys cylindrica feeding on worms it can only half swallow and then be trapped for hours with its head jammed in coralline algal turf waiting for the part of the worm it has swallowed to be digested. Another example is the large tun shells Tonna which feed on sea cucumbers, often larger than themselves. They somehow extend their head to envelope the whole sea cucumber and then have to sit for hours with their head swollen and unable to fit back into their shell.
Best wishes
Bill Rudman

Dear Maliza,
This is Roboastra luteolineata. This is a quite fast moving [for a nudibranch] hunter which feeds on other nembrothid nudibranchs [see message below].
Best wishes
Bill Rudman

Thanks Ross and Diane,
It really looks a happy Roboastra in the top photo.
Cheers,
Bill Rudman

Dear Ross & Diane,
What a wonderful find - though a bit sad for the Tambja. It is certainly convincing support for my view that the striped animal is a species of the nudibranch-hunting genus Roboastra rather than the bryozoan-feeding genus Tambja. Actually in your upper photo we can see the whole food chain, for at the bottom left I can see some small branches of the bluish arborescent bryozoan Bugula dentata on which Tambja verconis feeds.

Although we call the mollusc radula their 'teeth' they work in quite a different way to vertebrate teeth. A carnivorous vertebrate like a dog or a lion woud use its teeth to bite off or tear off chunks of flesh and swallow them. The mollusc radula can perhaps be compared with having teeth on our tongue. Although they can be manipulated in ingenious ways, molluscs have never evolved a way to use the radula to bite of large chunks. In carnivorous hunters the teeth have become a set of grappling hooks which can grab and hold on to their prey while the the 'oral tube' which is a very extensible region just inside the mouth, extends out of the mouth by turning inside out, and wraps itself around the prey. Once it has done this it can then pull itself and the prey back into its body for digestion.

I think this is the first record of anyhting feeding on Tambja verconis and I don't know of any observations of Roboastra luteolineata feeding in Australia or NZ. Atsushi Ono has a couple of photos of it in his book feeding on another species of Tambja in Japan.

Thanks again for sharing this very interesting observation.
Best wishes,
Bill Rudman

Thanks Scott,
Yes this is R. luteolineata. You can just see a bit of the oral tentacle in the shadow at the front of the animal.
Best wishes,
Bill Rudman

Dear Valda,
As I say at the top of the page I am not sure if this animal, which Debelius records from South Africa as T. luteolineata is really correctly identified or not. Typical R. luteolineata have a pattern of green markings which are absent in these South African animals. Perhaps it is a regional colour variation. It certainly has the prominent blue oral lappets typical of a species of Roboastra. As I say at the top of the page, Eliot's Nembrotha affinis has yet to be rediscovered.

I would call it Roboastra cf. luteolineata at present.
Best wishes,
Bill Rudman

Dear Ross and Diane,
I'm glad that 'non-professionals' find the Forum interesting. That is at least half the reason I do it. When I give talks to Dive Clubs or get phone calls from people telling me about some interesting animal doing this or that I only wish they had recorded it because often this is the only way the 'profesionals', who are very thin on the ground, can find out about the habits of these fascinating animals. Any photo of a slug eating, mating, laying eggs etc, or even being present in a place you've never seen it before, could be of interest.

It's no coincidence that most of the early theoretical ecology was done by ornithologists. They had a huge army of birdwatchers out there accumulating mountains of information on birds - what they ate, where they were, how many eggs they lay etc etc. So any chance I have of encouraging more pairs of eyes to study Sea Slugs I take it. I'm more than happy to share what I know if it encourages more people to take up 'slugwatching'.

I have added your info to the Participants Page.
Best wishes,
Bill Rudman.

Dear Ross,
Whatever Helmut Debelius has in his book, the only way to know what an animal is, is to have a look at its anatomy and to refer to the original descriptions of the species. I can assure you that the animal you have sent me photos of, has an internal anatomy which makes it a member of the genus Roboastra. Apart from other features the radular teeth are very distinct. When I get a new scanner I've bought to work, (I seem to have bought a lemon and I've threatened the manufacturer to tell you all the make and model if they don't make it work!), I aim to put some radular photos up to show you.

Another very distinctive feature is the long prominent oral tentacles which can be seen in the photo alongside. Now why isn't it Tambja affinis? If we go back to the original description of that species as Nembrotha affinis Eliot, 1904, he clearly illustrates the radula of a species of Tambja. That alone shows that your animal cannot be the same as Eliot's. Your animal is identical in colour and anatomy to Roboastra luteolineata as first described by Baba in 1936, and more fully by Hamatani & Baba, 1976.

There's not much more to say. I'm afraid that although books with lots of beautiful colour pictures are becoming quite abundant as the costs of colour printing fall, taxonomists and research workers studying these animals have not become correspondingly more abundant. Because of this, we will have to expect a level of inaccuracy in many popular works.

Researching the names, relationships and biology of most groups of animals is a slow time-consuming task. I know our 'clients', such as interested divers, photographers etc, are impatient for the correct name, but unfortunately until more funds are provided for basic research it will be a slow haul.

Bill Rudman.

Dear Ross,
Thanks for the photo. This is Roboastra luteolineata. As I have discussed at the top of the page, this species has often been identified as Tambja affinis in Australia and New Zealand. Its anatomy shows that it is a species of Roboastra and so can't be Eliot's Nembrotha affinis, which, from his radula description, is really a species of Tambja. Species of Roboastra are interesting carnivores which prey on other nudibranchs. One species on the west coast of North America actively hunts down species of Tambja. In Ian Skipworth's photo at the top of the page there is a little colony of the arborescent bryozoan which looks like Scrupocellaria (see inset here). I wouldn't mind betting that your Roboastra luteolineata is looking for species of Tambja on the bryozoan. If you want to advance "science" it would be worth looking out for any feeding encounters between Roboastra and the species of Tambja which you find in the same locality. It might be interesting to "set up" a meeting between the two with a camera at the ready!
Best wishes,
Bill Rudman.

PS: if you get any pictorial evidence I would love a photo for the Forum.