Onchidoris bilamellata

Craig Muirhead March of the Onchidoris bilamellata. A huge line (extending who knows how far in each direction). All heading exactly South. Today (13/10/13) near Oban. Depth 28m, water temp 12°C Where were they all going??

João Pedro Silva We've been having lots of demonstrations from the unions, too.

Leentje Vervoort To the Oban distillery

Bernard Picton They can smell some barnacles and they have eaten all the ones where they started....

Ian Smith Most impressive. Whatever the cause, barnacles or a dram, there is something that keeps them packed in line. Perhaps they follow each other's scent or slime trail? Supports old reports of mass migration, though even if it is upwards to breed onshore (early for that) it doesn't explain why they travel close packed like that.

Bernard Picton I've seen them doing this in Strangford Lough. I've also seen it suggested that by following closely they use a bit less energy producing a slime trail.

Craig Muirhead Do we know why? Is it like land animal migration; food and/or sex?

Craig Muirhead I've seen this in the past when the band has been tens of animals wide. Not just 3 or 4 like in the picture here.

Bernard Picton In Strangford there were areas where they had moved from, with plenty of spawn, barnacle scars and no adult nudibranchs. So I think it is to find more food...

Klas Malmberg Aquatilis Strange form of Onchidoris bilamellata or what else?

David Kipling Where was this from Klas?

Tamsyn MAnn Looks interesting...

Terry Griffiths Hi Klas, here is one from the South Devon lots of them this year plus lots of the pure white ones all mating, they all had variable amount of brown patching.

Klas Malmberg Aquatilis Picture taken at Väderöarna West coast of Sweden

Ian Smith Klas I think yours is most unusual and interesting. Did you get a shot of the underside by any chance? The oral veil is very large on O. bilamellata see http://www.conchsoc.org/node/6105 (click on it to enlarge). I find bilamellata is rather stiff with spicules and unlikely to flex up at the mantle edge like yours. I'd also expect more tubercles. And yours is rather wider than I'd expect, and though the colouration of O.b. is variable I've never seen the pattern of yours on the hundreds of bilamellata I've seen. I rather think it is an "or what", but don't know what! Nice find.

Bernard Picton Klas, is this very small?

Klas Malmberg Aquatilis I would say 10 mm Bernard Picton

Klas Malmberg Aquatilis Ididnt collect this one but just passed by it and took a picture because I thought it was different, new time i will take more pictures...

Tamsyn MAnn I know G'zillions is neither technical or scientific as a quantity, but there really are that many of these Onchidoris bilamellata about at the moment, all over Babbacombe in the silt! One of them was hitching a ride on a hermit crab!

Arne Kuilman Hard times for barnacles… (their diet)

Terry Griffiths Onchidoris bilamellata there was thousands of them today

Tamsyn MAnn did you see them on the bottom of one of the buoys? There were loads there last weekend, all over the massive tyre!

Terry Griffiths Out by the trawler lines.

Tamsyn MAnn Where are they??!!

Jørn Ari Is this Onchidoris bilamellata, the white version?

Erling Svensen I think it is a Onchidoris bilamellata.

Jim Anderson Looks like Onchidoris bilamellata to me.

Christian Skauge I agree, O. bilamellata :-)

Jørn Ari Thanks guys

Peter H van Bragt I guess I can only confirm O. bilamellata. We see little brown pigment mainly in juveniles. More rarely in adult specimen.

Erling Svensen The Onchidoris bilamellata is not often to see in South West Norway. Today I did see 4 of them in one spot. Very nice nudi that are quite difficult to observe.

Christian Skauge Good catch!

David Kipling We get hundreds of them at times, all laying spawn and munching barnacles. Very shallow though.

Jørn Ari It´s also common in Lillebælt - Denmark

Andy Horton I am surprised they are not seen on the shore off Norway. Seen in February, Sussex when they come into spawn. Variable numbers from year to year.

Eric van Andel Onchidoris Bilamellata Dutch waters, last year April :aproximately 1cm length.

Jørn Ari Is this Onchidoris bilamellata, the white version?

Erling Svensen I think it is a Onchidoris bilamellata.

Jim Anderson Looks like Onchidoris bilamellata to me.

Christian Skauge I agree, O. bilamellata :-)

Jørn Ari Thanks guys

Peter H van Bragt I guess I can only confirm O. bilamellata. We see little brown pigment mainly in juveniles. More rarely in adult specimen.

Mark Farrer Blairgowrie 21/7/12 5mtrs approx 20mm long

Mark Farrer Doris Cameroni (Allan 1947) I think

Henk van Dijk Onchidoris bilamellata?

Shôn Roberts Hi All. There is a Nudibranch in the centre of this photo but it looks just out of focus. Can anybody identify it please. Photo taken off Rhoscolyn Head

Richard Yorke How about Onchidoris bilamellata which feeds on barnacles

Liz Morris i dont know byut hes tiny weeny

Kate Lock Yes I will agree with Richard Yorke

Paula Lightfoot Is this Onchidoris bilamellata? It seems a bit darker than usual.

Christian Skauge No idea, but nice picuture :-)

Tony Gilbert It is quite dark for one,usually they are lighter brown than this. They feed on barnacles, and usually in aggregations.

Jim Anderson Looks like Acanthodoris pilosa

Christian Skauge Jim - yes it does! I have seen that one before :-)

Paula Lightfoot I didn't know Acanthodoris pilosa was also available in brown - but this photo of a brown specimen on the BMLSS website looks a bit like mine: http://www.glaucus.org.uk/seaslug1.htm

Becky Hitchin Paula Lightfoot - we only get them in brown down here!!

Paula Lightfoot At the same site this morning we found a more 'typical' (for the northeast anyway) white one, so I will record it as Acanthodoris pilosa. Didn't see any finger bryozoans but there were encrusting bryozoans on the same boulders where we found the nudis.

Peter H van Bragt Hello Paula, Acanthodosris pilosa indeed. On the Dutch coast we find them from white to black with various brown shades in between. Always monochrome. The spiky tubercles are most indicative as well the typical gills and rhinophores. cheers Peter H van Bragt

Godfried van Moorsel moreover, O. bilamellata has much more gills in a horseshoe

Penny Martin Loads of egg ribbons around here ... Onchidoris bilamellata??

David Fenwick Snr Probably best not to guess when it comes to eggs unless you find the species laying them as there are many species of sea slug. Also remember that some sea slugs eat sea slug eggs so they may not be the ones that laid the eggs in the first place. I've many beautiful images of mollusc eggs around the shoreline, sadly I cannot use or label any of these egg images until I see what's actually laying them. Best guesses don't make for good records either. Sea slugs and other marine molluscs photograph well but I'd love to see a colour guide to their eggs produced one day.

Darryl Mayer ID will also depend on the size of the ribbons. I'm having trouble visualising these pictures as the angles look strange. It does help with ID's if the subjects are oriented "normally".

Darryl Mayer I appreciate that (take the eggs of Coryphella lineata for example), but when it comes to ID'ing things, size, orientation, location, depth etc all helps. When we look at things (even underwater) we visualise things more easily when oriented "naturally". Just trying to help folks help others with their ID skills.

Andy Horton Onchidoris bilamellata is the most likely

Penny Martin Than you for all the comments .... this is the natural angle ... they are on horse mussels on the underside of a floating fishing pontoon approx 0.5 m underneath the surface ( but always underwater) I have seen O B around and there are empty barnacles .

Andy Horton http://www.glaucus.org.uk/ODoris.jpg

Penny Martin Onchidoris bilamellata again??

Chris Barrett looks like it, to me

Andy Horton http://www.glaucus.org.uk/ODoris.jpg

Chris Barrett Thanks Andy

Andy Horton Penny: were they recent photographs? I expect they are. Spawn laying i was recorded in March i on the Sussex coast. But I do not visit the shore in January.

Penny Martin Yes .... taken on Sat 22nd Jan

Andy Horton Late February and march breeding at the Mumbles, Swansea and March and May at Worthing, Sussex. More in May than March.

Terry Griffiths It's been a bit werid this year already have photo's of many speices laying eggs .

Chris Barrett Does anyone have any photos of the egg masses of Lipophrys pholis?

Bernard Picton We have a wreck, the Alistor, in Strangford, where they are often huge and spawning on New Year's Day (traditional New Years day dive).

Bernard Picton That's Onchidoris b. I mean, not Lipophrys.

Cat Wilding Can anyone help with an ID for this nudi please? Adalaria proxima or Onchidoris muricata? Neither of these have been recorded near the site before. From ~8m in mid-Fowey estuary, on a pontoon. This is the best photo I have in which the tubercles appear quite rounded, suggesting O. muricata? Cheers!

George Brown Have you considered Onchidoris bilamellata? The remains of many barnacles appear close by.

Ross Bullimore Yup... + 1 ..what George Brown said!

Fiona Crouch Yep that would be my first thought George and Ross.

Peter H van Bragt And indeed it is O. bilamellata.

Cat Wilding Awesome, thank you :)

David Kipling Palio nothus, taken in a rock pool in the Gower (Wales). All the intertidal ones I've seen have this sort of colour and the pointy tubercles, hence the ID. Apart from this being a particularly rubbish photo compared to Erling's (well, have you ever tried to get a dSLR and housing into a 20cm deep rockpool?!?) it does look very similar to me.

Gary Cobb This ID is correct.

David Fenwick Snr Your getting good at finding these David!

David Kipling Well first of all I discounted it because there were masses of barnacles around (this was on the tidal causeway at Worms Head) and I assumed it was Onchidoris bilamellata and didn't look too closely initially, I was too interested in the little Asterina in the bucket. I wasn't having a good day, since I first thought it was A gibbosa (wrong, it was the uber-cute A phylactica!) and a closer look at the nudi revealed my first thoughts were wildly wrong too! But we got there in the end. If you're coming to the Porcupine fieldtrip you can have a look yourself - it's in the same place.

David Fenwick Snr Sadly I rarely get out of county nowadays. I've only found the species once, at Spit Point, Par, near St. Austell, Cornwall; lovely site.

René Weterings Nice!! I have seen this species for the first time myself, yesterday in the Eastern Scheldt in The Netherlands. 2 times, 1 about 5mm long and 1 about 1cm long.

David Kipling David ... of course you were standing next to me when we found the one in the tic tac box at Carnsew, which we wouldn't have were it not for your local expertise for the hot spots.

David Fenwick Snr Yes found another hot spot the other day, which I surveyed pretty well, problem was the were zero nudibranchs, most surprisig. I went to a non-hot spot the day after and found four species under one rock. Nudibranchs can be so un-predictable LOL.

Arne Kuilman Dutch Acanthodoris pilosa at Kistersnol. A rare nudibranch in the Netherlands.

Brendan Oonk I'm sorry Arne but this is not A.pilosa but A white Onchidoris bilamellata

Penny Martin Loads of egg ribbons around here ... Onchidoris bilamellata??

David Fenwick Snr Probably best not to guess when it comes to eggs unless you find the species laying them as there are many species of sea slug. Also remember that some sea slugs eat sea slug eggs so they may not be the ones that laid the eggs in the first place. I've many beautiful images of mollusc eggs around the shoreline, sadly I cannot use or label any of these egg images until I see what's actually laying them. Best guesses don't make for good records either. Sea slugs and other marine molluscs photograph well but I'd love to see a colour guide to their eggs produced one day.

Darryl Mayer ID will also depend on the size of the ribbons. I'm having trouble visualising these pictures as the angles look strange. It does help with ID's if the subjects are oriented "normally".

Darryl Mayer I appreciate that (take the eggs of Coryphella lineata for example), but when it comes to ID'ing things, size, orientation, location, depth etc all helps. When we look at things (even underwater) we visualise things more easily when oriented "naturally". Just trying to help folks help others with their ID skills.

Andy Horton Onchidoris bilamellata is the most likely

Penny Martin Than you for all the comments .... this is the natural angle ... they are on horse mussels on the underside of a floating fishing pontoon approx 0.5 m underneath the surface ( but always underwater) I have seen O B around and there are empty barnacles .

Andy Horton http://www.glaucus.org.uk/ODoris.jpg

Judith Oakley also, quite a few groupings of spawning Onchidoris bilamellata, including these which were stacked high on top of a stack of Crepidula fornicata

Cynthia D. Trowbridge wild!!

Erling Svensen They are quite wild as they spawn out of the water, or? ;-)

Egidio Trainito you do not need to dive there, I see!!

Michael Southwood Dived Vera, there are 100's if not 1000's of Onchidoris bilamellata slugs on the boulders just south (about 5m) of the wreck and loads on the wreck. I doubt there will be a barnacle left by the end of the week.

Becky Hitchin Is this a fluke circular nudi egg mass? Or does some particular nudi make such a shape? (the bottom bit is a reflection, not a second mass)

George Brown Nice. Interesting. Where was this taken Becky?

Becky Hitchin Just outside Stonehaven on the low shore. That was the best photo I could get as it was way down in a crevice just at water level. Actually, there were quite a few strange "probably nudi egg masses" there today, all of which were impossible to get decent pics of. I really want to go snorkelling at high tide around Stonehaven

David Kipling They're not really cylindrical if you look closely but rather an overlapping ring. Not that this helps, as I still have no idea what it is! What nudis do you get round there?

Becky Hitchin I know ... but I only saw that when I looked at the photos ;) And not sure yet. Only seen the usual suspects so far

Ian Smith I've seen abundant Onchidoris bilamellata near Stonehaven. This could be a small specimen of spawn collapsed in as out of water. Northern locality and cold spring could account for rather late breeding. http://www.conchsoc.org/node/5372