Gregarious Jelly, Clytia gregaria
Look closely and you may see these tiny jellies boiling at the surface, or photo-bombing well planned underwater shots. They are indeed gregarious — in a prolific kind of way (especially in Spring and Summer). It is not uncommon to see them caught in the stomachs or tentacles of other jellies and this is well-illustrated in the photo of the Hanging Stomach Jelly with its prey. Often these appear to be clear and transparent with whitish radial canals, but a close-up will often reveal reddish pigment spots around their bell margin. For a complete description and more photos see inaturalist