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Mycale similaris

(Bowerbank, 1874)

René Weterings Geitodoris planata.....one of the "thousands" that can be found in the Eastern Scheldt at the moment in The Netherlands!

David Kipling Apparently it's supposed to have oral tentacles (not seen in A pseudo). Which I guess means flipping it on its back?

Niels Schrieken Correct David Kipling . But if you don't want to flip it over Geitodoris planata can be distinguished from Archidoris pseudoargus by the light coloured stellate patterns on the mantle (acid glands).

Niels Schrieken The third difference is that at the underside of Geitodoris planata there are brown spots on the mantle.

David Kipling (so we have to flip it again!). Can we see the acid glands in this picture Niels?

Niels Schrieken Yes at least four glands are very obvious. Between the branchial plume and the rhinophores.

Niels Schrieken :-). I am not sure if we should say to the divers to flip over all the animals they see.

David Kipling Me too ;)

Jim Anderson In the examples I have seen the top of the rhinophore tapers to more of a point in G. planata -it's a wee bit subtle but seems to be consistent. The star shaped acis glands are usually more obvoius. We saw many of this species at Loch Creran last weekend.

David Kipling I'm going to be obsessively looking at ever Archidoris pseudoargus I see now ...

David Kipling SSF has a useful pic showing those stellate spots, and some description of G. planata versus A. pseudoargus : http://www.seaslugforum.net/find/geitplan

Brendan Oonk Try to flip some of the pics over ;)

Jim Anderson René, Lovely image - they are difficult to 'catch' with the gill and rhinophores on show.

René Weterings Thank you Jim, but there are so many of these nudi's right now, that it makes it a bit easier to "catch" them in a nice position for photography!

Bernard Picton I'm very interested to know what they are eating. They seem to eat several species of Mycale (a sponge). In Strangford Lough Mycale similaris became much commoner in the last 20 years, followed by the appearance of G. planata, for which there were no historical records.

Bernard Picton http://www.habitas.org.uk/marinelife/sponge_guide/sponges.asp?item=C5540

René Weterings They eat "Mycale micracanthoxea" according to Peter van Bragt.

Bernard Picton Thanks René, I was interested to know if you had seen them on other Mycale species. 30 years ago we only found them on the bright red Mycale rotalis. M. micracanthoxea was only named in 1977 and I wondered if it might be an invasive species of sponge. I'm interested in observations of possible interactions between invasive sponges and tunicates and nudibranch predators.

Niels Schrieken http://www.anemoon.org/anemoon/spuisluis/2007/spuisluis/2001/011118.htm/?searchterm=Mycale%20micracanthoxea is showing the different characteristics of G. planata.

Peter H van Bragt Dear all, Mycale micracanthoxea is the only Mycale sponge found in Dutch coastal waters. It was most abundant in 1999 when G. planata first appeared in our southwestern estuary. Within 4 years the G. planata population exploded. We could locally easily spot 400+ individiuals on a single dive in the Eastern Scheldt and Lake Grevelingen. Some of remarkable size: up to 12 cm. Twice as large as reported in older literature. At that time the huge G. planata population almost completly depleted the Mycale population. Result was that in 2005-2006 G. planata almost completely disappeared, presumably due to food shortages, allowing the Mycale population to subsequently recover again. This recovery was supported by two relatively severe winters for which G. planata seems to be quite sensitive: 2009-2011. Bear in mind that the Netherlands is part of the northern distribution border of G. Planata and we have in the Eastern Scheldt and Lake Grevelingen a very extreme watertemperature window.: winter close to +1 degrees C. and in summer >20 degrees C. Only this year G. planata is quickly developing a dense population in the Eastern Scheldt again. At this moment >100 per dive locally already. Needless to say, at this moment Mycale micracanthoxea is very abundantly present again! Most likely the absence of predators and pathogens at the introduction in 1999-2004 contributed also to the populaion explosion and extreme sizes. Cheers, Peter H. Peter H van Bragt

René Weterings Thank you Peter!

Vinicius Padula Dear all, I have interest in study this species (G. planata). Could some of you collect 2-3 specimens?

Brendan Oonk Surely that will be posible. What do you need them for/(What is your study)?

Paula Lightfoot Hi, I'm just re-reading these interesting comments about Geitodoris planata as I've just been told of three records made on the Yorkshire coast in 2010 and 2012. I see there is a record from Brander Point St Abbs in 2007 although this record doesn't seem to have turned up on the NBN Gateway yet. Jim Anderson do you know if the St Abbs record has been sent to the Conchological Society? I'd be interested to know if anyone else has reports of this species on the east coast and what it might be feeding on here. The three Yorkshire records were found intertidally. Thanks Brendan Oonk for the brilliant photos showing the dark spots and oral tentacles, I am going to look very closely at any 'sea lemons' I find in future and these will be useful!

Jim Anderson Paula Lightfoot - I thought that I had notified them but may be mistaken. I have east coast (St. Abbs/Eyemouth) records of it from Oct 2004, August 2006, Jun 2007, July 2007 and June 2010.

Message posted on NE Atlantic Nudibranchs on 10 Oct 2012
João Pedro Silva From this morning's dive. Appears to be the same me and Gonçalo Calado found by the end of January (http://www.flickr.com/photos/jpsilva1971/6751608437/). I think it's relatively safe to say this sponge is its prey.

Bernard Picton Did you get a bit of the sponge João? If it was here I'd say Mycale rotalis, based on colour and surface appearance. Geitodoris planata seems to eat Mycale similaris in Strangford Lough, but Mycale rotalis in some other places. I guess it could be a red variant, you get that in Doris pseudoargus feeding on red Suberites ficus (assuming that it really is D. pseudoargus, A & H named it D. flammea).

João Pedro Silva I didn't collect it, Bernard. Although I can find the exact spot (to the cm) where it is. This is in a small wreck just outside the Sesimbra harbour.

Message posted on NE Atlantic Nudibranchs on 03 Apr 2012
Animalia (Kingdom)
  Porifera (Phylum)
    Demospongiae (Class)
      Poecilosclerida (Order)
        Mycalina (Suborder)
          Mycalidae (Family)
            Mycale (Genus)
              Mycale similaris (Species)
Associated Species