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Does look strange
I agree with Chris but I'd say a Moon Jellyfish (Aurelia aurita) a little decayed. An overall purple tinge (despite you note) and remains of the sub-umbrella (maybe)
If you agree, you should add another ID.
Rose, whilst you observed this in a Coastal location it is a Marine creature. You might get more response changing Habitat to Marine and adding Coastal as a Tag. This is a potentially valuable observation, thanks.
THREE MARINE PROJECTS
Lat/Lng: 54.3105, -5.5289
OS grid ref: SB705962
100's of these appeared around our shores and beaches over the weekend. They varied in size from a couple of centimetres to 10/15.
They are completely clear with only the milky white portion in the centre. No purple or blue tinges.