Euglena is a genus of single-celled flagellate eukaryotes found in fresh water and salt water. The cover depicts a portrait of Euglena viridis by the German naturalist, zoologist, geologist, and microscopist Christian Gottfried Ehrenberg (image published in “Die Infusionsthierchen als vollkommene Organismen. Ein Blick in das tiefere organische Leben der Natur.”, 1838; image retrieved via Flickr and modified by MIC). The cover is published under the Creative Commons Attribution (CC BY) license.