Dear Rick,

A few nudibranchs seem to have distinctive odors, but it's not a widespread feature. In most cases I suspect it is the result of secretions produced from breakdown products from their food. For example many species of Phyllidia produce a distinctive acrid, distasteful milky secretion when disturbed, which will kill fish and invertebrates in aquaria.

Sandra Millen [message #3195] mentions that Melibe leonina has a 'sweet fruity aroma' and the dorid Peltodoris nobilis a 'citrus fruit aroma', and Dave Behrens [message #16667] mentions Melibe and Acanthodoris lutea but I can't think of many others. Perhaps others will be able to add to the list.

Best wishes,
Bill Rudman

Dear Glen and Jackie,

Thanks for thinking of us Jackie. Melibe is a nice comparison to Gastropteron because as I am sure you know, their method of swimming is quite different. In Gastropteron lateral lobes of the foot act like wings or flippers, flapping up and down to provide thrust. In Melibe the whole body flattens so it looks like a vertical board turning the whole body into a blade which bends sideways to provide thrust. Bornella stellifer swims like this as well, as do some species of the quite unrelated dorid genus Plocamopherus.

A species of Bornella, has taken this a step further and instead of having a single bend in each swimming stroke it sends a wave of bends down its body so it swims like a snake or eel.  Scott Johnson gave it the very appropriate name Bornella anguilla [anguilla = eel].

Best wishes,
Bill Rudman

Dear Jackie and Glen,
Thanks for the great photos. We always appreciate new observations on the Forum.

Your question is a good one. Usually when individuals lay a series of ribbons like these, the coloration is identical. Sometimes the density of eggs within the mass can give a different look, but I don't see that here. Were all these masses laid by the same individual? Generally egg ribbons become smaller and less dense as a series is laid.

I hope this helps a little,
Dave Behrens

Dear Dave
Have a look at the Melibe leonina Fact Sheet where I note that Sandra Millen reports it. I have had a quick search of the literature and find a couple of references which show that the smell is caused by an aldehyde which Melibe makes from scratch. That is, it doesn't just steal a useful molecule from someone else, which is the usual nudibranch trick.

• Ayer, S.W. & Andersen, R.J. (1983)  Degraded monoterpenes from the opisthobranch mollusk Melibe leonina  Cellular and Molecular Life Sciences (CMLS), 39(3):  255 - 256. 
  [Summary:   2,6-dimethyl-5-heptenal  and 2,6-dimethyl-5-heptonic acid were isolated from skin extracts of the nudibranch Melibe leonina. The aldehyde (first molecule) is responsible for the pleasant odour of the animals.]
• Barsby, T. Linington, R.G., & Andersen, R.J. (2002) De Novo terpenoid biosynthesis by the dendronotid nudibranch Melibe leonina. Chemoecology, 12(2): 199-202
  [Summary. Show that 2,6-dimethyl-5-heptenal, a putative defensive allomone, is made by Melibe leonina via de novo biosynthesis.]

Bob Burn notes that the small Australian species Melibe australis  also produces a sweet musky smell when handled out of water. I have not noticed it when I have handled them, but that may be because I treat them very carefully as I am always scared they will drop all their cerata. Perhaps the synthesis of this sweet smelling aldehyde is found in many species of the genus. certainly something to look out for.

Best wishes,
Bill Rudman

Dear Jan,
Thanks again. I will be sad when their life cycle reaches its inevitable conclusion. I hope your regular reports on one species will encourage others to concentrate on life history studies of even their most common animals. I must say however, that the peculiar shape and feeding behaviour of Melibe give it a 'special uniqueness' - which may be a tautonymy - but if so, a very deserved one.
Best wishes,
Bill Rudman

Dear Jan,
I'm glad to hear that death has been postponed. You have definitely photographed them mating. As to what else you should be looking out for, I can't think of anything - if we had observations like this on populations of other nudibranchs we would be very  happy.
Best wishes,
Bill Rudman

Thanks Nicole,
Yes I had missed the egg mass. You are probably correct in assuming the egg mass suggested a reproductive stage has been reached in the population, and another message from Jan, which I am posting today [#15904 ] certainly confirms that.
Best wishes,
Bill Rudman

Dear Jan,
I know it's a natural part of the life cycle, but it will be quite sad to see them die off - your animals have almost become 'part of the family'. Looking back over your messages one puzzling thing is the lack of any large scale egg laying? Have I missed a message or have they missed a vital stage in their life cycle?
Best wishes,
Bill Rudman

Dear Jan,
Your illustrated reports have certainly opened our eyes to just how abundant  your Melibe leonina can be. I have included more of your photos - and your humour - in a second message [#15837].
Best wishes,
Bill Rudman

Dear Jan,
If two nudibranchs are together on the same surface then the only way they can have their right sides together is to arrange themselved head to tail. However if they are on opposite sides of the same stalk or leaf, as in your photos, then as long as the posterior half of their bodies is attached - sole to sole - then with a little contortion, their front right sides would easily be able to 'get together' when they are head to head. I don't know if they have succeeded in your photos, but they certainly seem to be trying hard.
Best wishes,
Bill Rudman

Dear Jan,
This message missed the Christmas rush - but better late than never. As you will see I've pulled out some of your earlier artwork. It deserves a wider audience than me.

Concerning the Melibe photos. I know in words that this species occurs in large numbers but your photo above really shows how dangerous it is to be a little planktonic animal - and even a crawling one - when Melibe leonina is in abundance.

Best wishes,
Bill Rudman

Dear Jan,
I passed this on to a crustacean expert, who by chance was in the USA for a couple of months and has only recently returned. He tends to think your animal is an isopod crustacean, but doesn't recognise a family grouping from the photos. He would need a specimen to identify it but as I told him, the specimen cruised past some time ago.  I tend to agree with your suggestion that this is not a regular association. Considering Melibe's partiality for small crustacea, I think it may have a death wish
Best wishes,
Bill Rudman

Dear Jan,
I must say that species of Melibe are one of my most favourite animals. Their shape is so unbelievable - but clearly very efficient. You ask if they are 'feeding off' the Eel Grass. If you mean are they eating the Eel Grass, then the answer is no. They have no teeth or hard parts so biting off bits of plant material is out of the question. All species that have been looked at feed in small crustacea - crabs, shrimps, copepods, amphipods etc, which they catch in their remarkable fishing net-like oral hood. Most species feed on crustacea living on the sand or substrate which they catch by feeling with the papillae (or feelers) along the edge of their oral hood, closing the hood around the prey and swallowing it whole. Melibe leonina also catches planktonic animals drifting past by holding its head out into the water current.

In your wonderful photos, the animal it is 'slurping' along the Zostera leaves attempting to catch any small crustacea living amongst the organisms growing on the leaves.
Best wishes,
Bill Rudman

Thanks Ingo,
Bill Rudman

Dear Jan,
Firstly, thanks for the wonderful cartoon! I'll have to make you the Forum's 'official cartoonist' - no salary unfortunately. Thanks also for the interesting observation and photos. I've include some in a second message [#14889 ] as we have to restrict the number of images per message.

Species of Melibe, and some other opisthobranchs are able to drop some of their cerata, and other body parts as a defensive measure - a bit like some lizards drop their tails. It is called autotomy. Not much is known about regrowth of body parts. There is a big paper by Bickell-Page (1989) on ceratal autotomy, which investigates the complex processes in both the nervous system and the muscles, which is needed for autotomy to occur. But from memory I am pretty sure no mention is made of regrowth. However there is a paper on ceratal loss in our old friend Hermissenda crassicornis (see Miller & Byrne, 2000) which did study regrowth, and they showed that Hermissenda can fully regrow its cerata in about 40 days. An earlier study by Kress (1968) on a number of species of Doto, showed it took between 30 and 60 days for full regrowth depending on the species. When you think this means regrowing the internal digestive gland as well as the cerata, with all the skin glands etc, it is quite a complex process. Most nudibranchs can survive periods of starvation, often by absorbing their gonads so I suspect no great harm will come to the Melibe as it regrows its cerata. As you can see in your photo,  Melibe leonina also has branches of the digestive galnd in its body wall as well as the cerata, so its not totally bereft of a gut even when it loses its cerata.

• Bickell-Page, L. R. (1989) Autotomy of cerata by the nudibranch Melibe leonina (Mollusca): ultrastructure of the autotomy plane and neural plane and neural correlate of the behaviour. Philosophical Transactions of the Royal Society of London, B 324: 149-172.
• Kress, A. (1968) Untersuchungen zur histologie, autotomie und regeneration dreier Doto-Arten Doto coronata, D. pinnatifida, D. fragilis (Gastropoda, Opisthobranchia). Revue Suisse de Zoologie 75: 235-303.
• Miller, J. A. and Byrne, M. (2000) Ceratal autotomy and regeneration in the aeolid nudibranch Phidiana crassicornis and the role of predators. Invertebrate Biology 119: 167-176.

Best wishes,
Bill Rudman

D. Animal, drifting and swimming, in the currents before the calamity with the sea anemones.

Thanks Jan,
Your animals have the same white patches as in Marli Wakeling's earlier photos [#10999]. It would be interesting to know what they are.
Best wishes,
Bill Rudman

Dear Ron,
I've doctored your photo a bit to show some of the detail - photographing transparent animals in a white bucket is not that easy. It is Melibe leonina. If you look at the species Fact Sheet, and some of the attached messages, you should find quite a bit of information on the fascinating animal, which uses the large oral hood as a shrimp net.
Best wishes,
Bill Rudman

Dear Steve,
I summarised in an earlier message #3511 what we know of this animal's life cycle. I don't think longevity has been studied. Hopefully someone will be able to help us.

• Ajeska, R A. & Nybakken, J (1976) Contributions to the biology of Melibe leonina (Gould, 1852). The Veliger, 19(1): 19-26.

Best wishes,
Bill Rudman

Dear Jen,
Although all nudibranchs are carnivorous, their larvae, if free-swimming, all feed on single-celled algae. Usually in laboratories, commercial single species cultures are used.

You are fortunate that Melibe leonina is one of the few species whose larval development and metamorphosis has been studied in any depth. Bickell & Kempf (1983) fed their veliger larvae a commercial alga culture of Pavlova (Monochrysis) lutheri and when they metamorphosed into tiny crawling slugs, fed them unidentified ciliates which were cultured on rotting animal tissue, and supplemented this diet with the nauplii larvae of harpacticoid copepods.

• Bickell, L.R. & Kempf, S.C. (1983) Larval and metamorphic morphogenesis in the nudibranch Melibe leonina (Mollusca: Opisthobranchia). Biological Bulletin, 165: 119-138.

Are you planning to culture them yourself? If so, keep in touch, and let us know how you go.
Best wishes
Bill Rudman

Thanks Bruce
They are fascinating animals. You certainly can see the branching digestive gland very clearly in these animals. Apparently you saw no sign of the white patches that Marli Wakeling reported recently.
Best wishes
Bill Rudman

Thnaks Ali,
Bill Rudman

Dear Marli,
The little white spots are almost certainly glandular, but I have no idea what the large white speckled patches are. There is always the possibility that they are some minute flatworm infesting the slugs but that is just a guess.

I have included a closeup of the rhinophore and its very characteristically shaped sheath
Best wishes
Bill Rudman

Dear Melissa,
The only thing I can think of which fits your description is Melibe leonina, but I don't know if I would describe its colour as purple although I guess the iridescent sheen which appears on the skin in certain lights, could be described as purple. Let me know if I've guessd correctly
Best wishes,
Bill Rudman

Dear Kenny,
Apparently you didn't find the page on Melibe leonina. Have a look there and at the messages attached at the bottom of that page (below your message) and I think you will the information you are looking for. In particular have a look at my reply to William Cullen's message.

If you are looking for things in the Forum you can use the SEARCH button, or any of the other buttons at the top of this page. You can also click on any underlined word as well.
Good Luck with your project,
Bill Rudman

Dear William,
Please thank Sherstin for the wonderful poem. It must be one of the very few poems about sea slugs. I look forward to your photos.
Best wishes,
Bill Rudman

Dear William,
Although I have never seen it alive, from what I have read and seen in photographs, I can well understand why you and your family find Melibe leonina fascinating. Quite a few people have studied aspects of its biology and I have listed most of the background information on the M. leonina references page. I am not sure how familiar you are with using webpages so in case you aren't very familiar, if you click on any underlined word, which will probably also be in a different colour, you will open another page on that topic.

To answer your questions. The larvae of all nudibranchs, all molluscs in fact, are quite different from the adults. They are called veligers, and have a shell and a large bilobed ciliated flap (velum) on the head which is used for swimming and for catching the microscopic plants that veligers all feed on. If you go to the General Topics List and look at the pages listed under 'larvae, larval development etc' you will find some photos of veliger larvae and how they develop into slugs. Also have a look at some good photos of the larvae of Hypselodoris zebra. In general if you want to look for things on the Forum use the SEARCH button at the top and bottom of each page and type in the word you are interested in.

Now getting back to Melibe. Veliger larvae hatch from their eggs about 10 days after laying. Like all veligers, they have a shell, operculum, velum etc., and they swim in the plankton where they feed on microscopic plants (phytoplankton). After 30-59 days they are ready to metamorphose, which means they are ready to settle out of the plankton, change shape and become little crawling slugs. Most nudibranchs that have been studied, need a chemical scent in the water, usually from their food, before they begin to settle and metamorphose. In Melibe leonina however, a chemical stimulus does not seem to be necessary. Metamorphosis is a major event for all nudibranchs, because they not only have to change shape but they have to change their digestive system and how it works, because they are changing from eating plants to eating meat.

After settling on the bottom, the small slug begins to change shape. After 12-20 hours it drops its shell and it is rapidly growing its oral hood and the first pair of cerata. Within 2 and a half days the oral hood is big enough for it to catch its first meal, which because it is still very small, consists of microscopic one-celled ciliated animals.

Which brings me to your question about the tentacles on the oral hood. Melibe leonina, like all species of Melibe, uses its oral hood like a throw net in fishing, to catch its food. The fine tentacles along the edge are used to feel for prey. When prey are detected the net can rapidly close, drawing the food into its mouth. Melibe leonina eats small crustacea and other small invertebrate animals, but large and small Melibe use the hood quite differently. Larger animals (25mm or longer) feed by lifting the oral hood into the water column and waving it through the water, regularly closing it to eat any animals which have been caught. The more prey in the water, the more often Melibe will go through the feeding cycle of waving and closing the hood. Small Melibe, less than 25mm long, seem to feed quite differently. They hold the hood out horizontally, just above the bottom, and gradually move along feeling ,with the tentacles around the edge of the hood, for small prey. This is the way that other species of Melibe, such as M. engeli and M. viridis feed, even when they are much larger.

There are very few observations of animals attacking and eating M. leonina. The only one I can find reports some of them being eaten by the Kelp Crab Pugettia producta in Monterey Bay, California. (Ajeska & Nybakken). M. leonina is well-known for the characteristic citrus smell it produces when touched or when it is aggregating in large numbers. This secretion is produced by skin glands in the oral hood and cerata and consists of a weak acid and a scent. Some consider it to be defensive, and it has also been suggested that it is a sex pheromone, attracting animals together for mating, but no one really knows. I don't know of people eating it. I would suspect the secretions from its skin would make it rather distastteful.

What else can I say about it? It can swim by lateral flexion of the body, but swimming seems to be a second best way of life, probably as a result of being washed off the plants it normally lives on. I almost forgot your question about the cerata. I am not sure what their function is, but they certainly increase the surface area of skin so are important in respiration (breathing, gas exchange)and so could be thought of as gills. One other important function of the cerata is probably defence. When disturbed, Melibe can break off one or more of the cerata, which then wriggle around and exude their characteristic secretion and scent for some time. This behaviour, much like a lizard dropping its tail, is called autotomy. Have a look at the autotomy page for some other examples of sea slugs which use autotomy in their defence.

Have a look at the information and photos on other species M. engeli and M. viridis. I hope this will give you plenty of information for your project. Perhaps if you take any photos of your Alaskan animals you could send a copy to the Forum, or if you see them doing interesting things, you could let us know
Best wishes,
Bill Rudman

Dear Melibe,
I never thought I would ever have a conversation with a Melibe! Although they are fascinating animals and have a very clever way of catching their prey, I don't think they really have the brain capacity for language.

I hope your message doesn't start an avalanche of "My name is Doris" type messages, as I am having enough trouble with the backlog of questions on real slugs. I guess naming people after slugs is completing the circle, as many slug names are directly from the names of Greek and Roman gods and goddesses.
Best wishes,
Bill Rudman

Glad to help Mike,
and thanks also to Bruce Wight who was able to rustle up some excellent photos at short notice.
Best wishes,
Bill Rudman.

Dear Michael,
I am not sure what the kite-shaped thing at the left-hand end of your photo is, but I am pretty sure this is the fascinating Melibe leonina which is found from Alaska to California. It is often found attached to kelp but is also found floating/swimming freely in coastal waters. Its jellyfish-like head is in fact a large fishing net used to catch the small shrimp-like crustacea (amphipods etc) that it eats.

I asked Bruce Wight if he could provide any photos to help identify your animal and he has kindly sent me some. Thanks very much Bruce. There are already photos of a couple of species from the tropical Indo-West Pacific already on the Forum [Melibe viridis and Melibe engeli].

Best wishes,
Bill Rudman.