The shapes can seem to appear out of nowhere: an undulating S-like spiral streaking across the European skies or a glowing orb trailing above the North American coast. Such strange light shows ...

Shell (A) and operculum (B) measurements. (al) Aperture length, (aw) aperture width, (bw) body whorl, (ol) operculum length, (ow) operculum width, (tl) total length, (tw) total width. For histology of ...