Dear Mike,

This is a primitive sea slug called Umbraculum umbraculum. If you have a look at the Fact Sheet, and the messages attached to that page, you will see photos which show many aspects of its anatomy and biology. It does have a shell - it is round and flattened and sits on the top of the animal. In your photo it is covered in sea weed and associated mud and silt. There is a large gill hidden under the right side of the shell and until recently Umbraculum and its relative Tylodina were considered the most primitive of the side-gilled slugs or pleurobranchs, which also have a gill on the right side, but we now think they are two unrelated groups.

Also the siphon you can see is in fact one of a pair of head tentacles. You are right to compare it with the siphon of carnivorous snails like the volutes, because like their siphon it is a hollow enrolled tube used to suck water into the mantle cavity and gills. While their primary function is to provide oxygen rich water to the gills, the water also passes over sensory regions so that both animals can 'smell' chemicals in the water which can lead them to their food.

Best wishes,
Bill Rudman

Thanks Floris,

Some limpets do have papillae a bit like illustrated and I did wonder about Haliotis. The biggest problem is not knowing how accurate the illustrations are. For example the three pairs of head tentacles are a puzzle.  I am afraid that without a specimen we can only guess.

Best wishes,
Bill Rudman

Dear Floris,

It would be valuable if you could give me the name of the book and author to include with your message.

The first problem is we have no idea just how accurate the artist [or engraver] was. It certainly could be a snail or slug with a limpet-shaped shell and there are indications it could be Umbraculum, but if the frilly row of papillae are suppose to represent the single gill of Umbraculum, then the papillae should run above the head and tentacles in an unbroken row. Also if you look at some of the photos of Umbraculum you will see that the head and 'snout' are not as in this illustration. Another possibility is another limpet-like slug, Tylodina americana. I don't have any photos on the Forum but have a look at Tylodina corticalis which has a head more similar to the illustration.

The other possibility is that it is some type of limpet. I'm afraid I can't easily identify the 3 pairs of tentacles [a,b,c]. Perhaps they are not accurate? Are shells illustrated in the book? I suspect if it had a shell it would have dropped off in the 'preserving jar' and if it didn't dissolve in the 'liqour' perhaps it was dried and drawn separately?

Best wishes,
Bill Rudman

Dear Leanne and David,

Photos of animals 'doing things' are always welcome, and it especially valuable to get another photo of Umbraculum egg-laying. As you imply from your message, the bright colour of the egg certainly draws attention to the animal. What is just as remarkable is just how camouflaged in colour and texture the animal is on what is apparently its food sponge. The growths covering the shell complete the illusion that Umbraculum is just part of a sponge colony.

Best wishes,
Bill Rudman

Dear Heidi,

Yes this is Umbraculum umbraculum. They have a considerable range in colour from pale translucent whitish, through yellow, to bright orange. Often their are large whitish pustules but sometimes like your animal, the pustules are smaller and the same colour as the rest of the body. I suspect the colour of individuals is associated with the colour of the sponges they are feeding on, perhaps through the transfer of sponge pigments to the Umbraculum, but that is an idea, not a Fact!

Best wishes,
Bill Rudman

Dear Kent,

This is Umbraculum umbraculum, a strange primitive sea slug with few close living relatives. It is not a dorid nudibranch and was long thought to be related to the pleurobranchs or side-gilled slugs because like them it has a large single gill on the right of the body. However recent studies suggest it and Tylodina are more closely related to the nudibranchs than the pleurobranchs.

The structure which puzzles you on its back is its umbrella-shaped shell, from which it gets its name. Have a look at an ealrier message from New Zealand [#12844] where I label some of the basic parts of this animal. And of course look at the species Fact Sheet and the other messages attached to that page.

The orange 'blob' you can see on the back of the animal, behind the shell, is faecal material. Not perhaps a 'polite society' topic but a good clue to its diet of a group of sponges of a similar colour. Although very obvious when out in the open, Umbraculum can squeeze itself into some most unlikely crevices, and sometimes into cavities it has eaten in a large sponge colony. In these situations, its dull coloured warty back, and the shell, covered in plant growths, render it almost invisible. In the photo alongside it looks as though there is a second half-hidden animal at the bottom right corner, looking a bit like a contracted sea anemone.

Best wishes,
Bill Rudman

Thanks Hugues,
I guess the sizes you give are shell lengths? It is interesting how your animals seem to be without any growths on the shells, while in some parts of the world the shell is always covered in algae and colonial animals. Thanks for the photo of the mouth [middle left photo]. I have added a close-up [middle right] to show the front of the body. You would expect the mouth to be up near the eyes and head tentacles [rhinophores] which can be clearly seen at the top of the body, but in this strange animal the mouth is far away on the sole of the foot. Running down the front of the body, from the eyes to the mouth, is a deep vertical groove, which contains the openings of the reproductive system

Best wishes,
Bill Rudman

Dear Ian,
I am glad you didn't try too hard to rub off the sand because this is Umbraculum umbraculum which is a rather primitive slug with a round limpet-shaped shell in the middle of its back. What you were trying to rub off was the sand and growths that often accumulate on its shell.
Best wishes,
Bill Rudman

Dear Leanne & David,
Thanks for these interesting photos. I am not sure of the identity of your sponge, but in New Zealand they feed on a variety of spiculate sponges such as Aaptos, Tethya and Ancorina. The white material at the edge of the sponge 'wound' looks interesting. It looks like the skeletal stucture of spongin and siliceous spicules which hold the sponge body together. I don't knonw if this means Umbraculum has regurgitated this or what. My understanding was that the slug bit or scraped off chunks of sponge and swallowed them undigested. I certainly have seen its faecal pellets which consist mainly of nicely arranged bundles of sponge spicules, showing that it certainly eats some sponge material whole.

If you have any clues where the white material comes from I would be interested
Best wishes,
Bill Rudman

Dear Bruce,
Yes it is not often that you see a large specimen out in a 'posing' position. If you see one feeding, I wouldn't mind some photos of one in action.
Best wishes,
Bill Rudman

Dear Unni,
It's surprising what survives in 'live rock'. This is a 'side-gilled' slug called Umbraculum umbraculum. You'll see form the Fact Sheet that it has a flattened conical shell, often covered in plant growths, as in your animal. It is obviously a juvenile.
Best wishes,
Bill Rudman

Dear Trev,
This is the primitive side-gilled slug, Umbraculum umbraculum.  It looks quite like the Wandering Sea Anemone, Phlyctenanthus australis, which is often found attached to kelp, here in New South Wales. I am pretty sure there is a similar, if not the same anemone in New Zealand. It also looks very like the large dorid nudibranch Archidoris wellingtonensis, which is definitely found in New Zealand. However its closest relatives are the side-gilled slugs such as Pleurobranchus and Pleurobranchaea. If you look at Paul Furneaux's message [#10615] concerning Pleurobranchaea maculata from New Zealand, you will see from the photos why they are called side-gilled slugs.

I have included a couple of close-ups from your photo to show the large external limpet-like conical shell, and the large gill which lies under the shell arround the front and down the right side of the body. Usually the gill is hidden under the shell, but when the animal is feeling safe, it can extend the gill out from under the shell as in your photo [lower right]. The whole body is covered in conical pustules as can be seen in your lower left photo.

Best wishes,
Bill Rudman

Dear Sue,
Thnaks for the interesting and unusual view of the head of Umbraculum. As I have said before, our knowledge of the external shape of the head region is based on the dissection of preserved animals and unfortunately when they are preserved they tend to contract and the muscular bosy wall becomes stiff and rigid, making interpretation of the anterior structures very difficult. I can find no intelligible drawings showing these features. In your photo the pair of yellow flaps which are joined to form a tube in the midline are oral flaps or tentacles on either side of the mouth.
Best wishes
Bill Rudman

Dear Leanne & David,
Thanks for filling another gap. In fact in your close-up alongside I can see a very interesting thing. If you look carefully at where the egg ribbon is emerging you can see it is coming out of a flap of tissue which has previously been identified as a permanent external penis. [see earlier photos]. It looks here as though this structure may be related to similar flaps of tissue found at the genital opening of the pleurobranchids, rather than being a penis. I'm afraid some anatomical structures are very difficult to interpret in preserved, often distorted animals. In the case of Umbraculum the structures at the front of the body lie in a groove in the extremely muscular body wall. When tha animal is preserved, the muscles of the body wall contract - even if the animal is 'put to sleep' first - so it is almost impossible to see this region clearly. All we need now is someone - an intrepid naturalist/diver - to gently pull two mating animals apart to see just what goes where during mating.
Best wishes,
Bill Rudman

Thanks Mary Jane,
The eyes and the typically rolled rhinophores are clearly visible in your photo alongside
Bill Rudman

Dear Valda,
The prevailing view is that there is one species in the Indo-West Pacific and its earliest name is Umbraculum umbraculum.
Best wishes,
Bill Rudman

Dear George,
This is a very brightly coloured example of Umbraculum umbraculum. It looks very much the same in colour to a photo I have at the top of the page from Tanzania. In eastern Australia, at least, this species can be found from the intertidal to a depth of at least 274 meters where it is completely colourless.
Best wishes,
Bill Rudman

Dear Peggy,
Thanks for thinking of the Forum, and thanks to Ross for taking the photos. Tom Thompson (1970) reported some facts and figures about an egg mass produced by a 16cm long animal from N. Stradbroke Id, Queensland. The uncoiled ribbon was 100cm long and 22mm high. The number of egg capsules per cm was 46,000 and there were on average 37 eggs in each capsule. This gave a grand total of over 4.5 million eggs in the whole ribbon. Hartley (1964) also published an account of egglaying and early development.

It never ceases to amaze me that this species can be found from the intertidal to 274 meters deep. One advantage of photographing the animal out of water is that you can see parts of its anatomy which are normally hidden by the shell. In the upper photo the umbrella-like shell is lifted to expose the smooth pale coloured cavity which is usually filled with water and encloses the gill which lies along the right side of the body. In this photo the gill is still hidden beneath the shell. I have also included an enlarged version of this photo showing the head region and its anatomy in a separate message.

Thanks again for this interesting find,
Best wishes,
Bill Rudman

References:
• Hartley, T.W. (1964) Egg laying and early development of Umbraculum sinicum Gmelin. J. Mal. Soc. Aust., 8(15 December): 33-35.
• Thompson, T.E. (1970) Eastern Australian Pleurobranchomorpha (Gastropoda, Opisthobranchia). Journal of Zoology, London., 160: 173-198.

Dear Akos & Donata,
Thanks for the photo. If you have photos of Umbraculum laying eggs or eating a sponge, or get the opportunity to take some, they would be very interesting.

Best wishes,
Bill Rudman.

Dear Johan,
I think they are very specialised in their choice of food, and in my experience the sponges they feed on don't survive well in aquaria. Personally, if you can put them back where you collected them, I would do that. Although it might sound a bit strange, one interesting thing to look at are the faecal pellets of Umbraculum. I have never seen it described in the literature, but specimens I looked in New Zealand suggested some sophisticated sorting was going on in the stomach. Each faecal pellet consisted of many bundles of sponge spicules, all packed together into a cylinder. Each spicule bundle consisted of a neatly stacked cluster of spicules arranged like a neat pile of firewood, the spicules all about the same length, each bundle in a little mucous case. Along the edge of the faecal pellet were four or five streaks of orange or yellow which I presume was the waste from the sponge tissue. Somehow the digestive system sorts out the spicules and stacks them into neat bundles, then wraps each bundle in a mucous sac, then packs a number of bundles to make a faecal pellet.

Best wishes,
Bill Rudman.

Dear Johan,
I'm afraid the 'grab' from your video doesn't give me much help, but I think from your description you have found a couple of Umbraculum umbraculum. Have a look at the photos at the top of the page. These are not nudibranchs, but they are Sea Slugs, belonging to a separate Order, the Notaspidea, sometimes called the Side-gilled Slugs.

If my identification is correct, the 'marine rock' on their backs is in fact their shell, which is often overgrown with other marine life. Let us know if I have guessed correctly.

In future I am happy to look at real photos, but I suspect for most slugs, video frame grabs won't give me enough information even for a guess.
Best wishes,
Bill Rudman.

Yesterday we received a frozen Umbraculum umbraculum from 203m from off the southern part of the Great Barrier Reef. It was sent by Alan Limpus, a well known shell-collector, who thought it rather unusual. The photos I have taken of the freshly dead animal (Shell length = 7cm) show its translucent white colour.

I know of no published records of such deep water specimens of Umbraculum umbraculum, an animal normally considered to live intertidally or in scuba depths. In the Australian Museum, we have records of dredged specimens from off southern New South Wales at depths ranging from 30 to 274m, suggesting it is widely distributed across the continental shelf. The deeper water specimens are all very pale coloured. Perhaps the colour of the animals is dependant on pigments obtained from their food sponges? Intertidal Umbraculum range from bright orange to yellow and dull brown. Perhaps the deeper water sponges it is eating are often pale or colourless?

The full locality details are: 25 miles East of the Swains Reefs, Great Barrier Reef, Queensland, Australia. 203m Trawled by FV Nelissa Jay, March 1999. Presented by Alan Limpus. (Photos: Bill Rudman)

Bill Rudman.