100 yards down the chalk reef - and a different colour Idotea. Same sp though.
No interactions present.
Graham I am trawling back through some Marines (as you do!)
Do you think, in picture one, the tail segment MIGHT be 'tridentate'? If so it points to I.baltica.
...generally the tridentate is obvious - pic 2 bit more obscure but hone in looks just the single point (same animal).
Well I'm still not too certain.
If you look at the incredible outer-corner smoothness of Picture 5 in http://www.ispotnature.org/node/402610 and compare with balthica (in picture 3) upper side you can see that yours MIGHT have a triple posterior border - might, I say. Seeing them together, as I did, allows for a more informed ID. And a photo of the underside posterior is best.
Lat/Lng: 51.3831, 1.3262
OS grid ref: TR315701