This is probably a sea slug. Was found in rock pool in rocky shore, Co. Waterford, southern Ireland.
No interactions present.
Sea slugs are not at their best photographed out of water. A scale would have helped too although judging by the size/age of the barnacles this is quite a big animal.
If forced to guess a name then I'd go for the Sea Lemon Archidoris pseudoargus on the basis of size and colour and the coarse tubercules covering the body.
It looks too big to be Onchidoris, a genus in which most species tend to be white or cream. However, O bilamellata is a barnacle feeder in which the white background often has brownish patches.
Having seen many O.Bilamellata (& more pictures),I've never seen any red or yellow in them; & from the habitas website they're our largest Onchidoris ,up to 4cm,& the others only up to 1.4cm. So I'm certain it's a sea lemon
Both Marlin & habitas (as well as EOL) say the species most likely to be confused with Archidoris is Geitodoris planata, with stellate spots on dorsum & brown specks on the underside of the mantle. (apart from all orange A.p's & rostanga rubra).
http://www.discoverlife.org/mp/20q?search=Geitodoris+planata shows 13 pics of G.planata, including spotty mantle underside
If you take out the under 35mm, the aeolids & the patently different (like Greilada elegans),only Jorunna tomentosa is left & google images shows it's nothing like. I.e. no other uk species can look like this.
(& both MarLIN & habitas say Onchidoris bilamellata is white/ dirty white & brown & google images show how totally different it is. See http://www.habitas.org.uk/marinelife/species.asp?item=W13320 (they all look like that in google images)
The detailed descriptions in http://www.conchsoc.org/spAccount/geitodoris-planata (took long time to load) & http://www.conchsoc.org/MolluscWorld21/3 give a full account how different the sea lemon is from jorunna tomentosa & Geitodoris planata
Thanks for your invitation http://www.ispot.org.uk/node/318553#comment-112797
to visit here Chris. I cannot help much, except to say that here in Orkney, the sea lemon (Archidoris pseudoargus) is as variable as it seems in this post.
Certainly this one has the structure of it but it is a little blotched for comfort.
Though see this one http://www.conchsoc.org/node/5657
Thanks for that link, Dejay. a fuller view of the same in all it's blotchy glory is at http://www.conchsoc.org/spAccount/archidoris-pseudoargus
I came back after your Forum thread (about this post)
It's doubly interesting for me because Andy's ID is slightly more correct than yours, as even then he knew the name had changed (I see you have courteously agreed). Also the iSpot computer knew about the synonymy (the drop-down still testifies to that).
But the issue you mention (icon score) does seem hard to explain. I think it might be to do with you vs Murdo as the ID Presenters. Hopefully then a high iconned visitor will come (actually I know that Murdo still comes and might see this comment)
Later. I tried my hand by moving my agreement to Andy's (like JoC) but it has still not shifted Likely.
PS I have shifted Likely; it was with Syrphus (today May 2015). I took my agreement from Andy and added it again to Chris's. I might put it back to Andy's and see if Likely stays with Chris's (it has - hooray then)
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