A group of freshwater triclads photographed in situ, in a shallow, spring fed Cotswold stream. The one top right is shown in more detail.
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I agree it looks very much like P. felina with a distinctive horned head-shape when moving.
Either Polycelis felina or Crenobia alpina, and if the photographer saw lots of eyes, then the former.
Lat/Lng: 51.9, -2.1
OS grid ref: SO9925