SEM microscopic image Sphaeroforma arctica, a unicellular with a central role in the tree of life. First isolated isolated from the arctic marine amphipod Gammarus setosus, Sphaeroforma arctica are spherical cells with the capacity to grow into multi-nucleated coenocytes (image by Multicellgenome Lab, University Pompeu Fabra, Spain; image retreived from Flickr and modified by MIC). The cover is published under the Creative Commons Attribution (CC BY) license.