Marine Flatworm

Marine Flatworm

Observation - Marine Flatworm. Description: Certainly a flatworm and certainly with two eyes and a ridge along its back. http://www.polarlife.ca/organisms/inverts/marine_inverts/turbellarians.htm and http://species-identification.org/species.php?species_group=marine_planarians&menuentry=soorten

Certainly a flatworm and certainly with two eyes and a ridge along its back.
http://www.polarlife.ca/organisms/inverts/marine_inverts/turbellarians.htm
and
http://species-identification.org/species.php?species_group=marine_planarians&menuentry=soorten&id=69&tab=beschrijving

Whilst 'Arctic' it is said to occur in European waters (Species-identification.org) but NBN doesn't recognise the name nor, I should add, does it appear in the hitherto definitive handbook by Hayward and Ryland.
On the face of it the specimen here is larger than it ought to be, at 30mm, but most other features seem to match.
Picture 6 shows how flat it was but also how it moved in the hand.

Another marine flat worm appears at http://www.ispot.org.uk/node/126704
Leptoplana tremellaris may fit all the criteria but it does not occur (NBN) north of Douglas (IOM)
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Core edit
corrected two words