, Eldonia ludwigi, an early deuterostome that may show features of pre-echinoderms; magnification, 1.1x. Specimen from Middle Cambrian , British Columbia. b, Undescribed worm from Middle Cambrian , British Columbia, possibly representing an early annelid; 3.2x. c, Articulated halkieriid from the Lower Cambrian of the Sirius Passet fauna, north Greenland; 1.5x. Halkieriids appear to represent a very early stage of mollusc evolution. d, The priapulid worm Louisella pedunculata from the Middle Cambrian , British Columbia; 0.85x. The trunk bears rows of sclerites, closely similar in arrangement to those of palaeoscolecidans. e, Spriggina floundersi, with segmented body and cephalic shield, a possible member of the arthopod stem group from the Vendian Pound Subgroup, south Australia; 2.3x. Bcl-2 blocks apoptosis in cells lacking mitochondrial DNA Michael D. Jacobson, Julia F. Burne, Michael P. King, Toshiyuki Miyashita, John C. Reed &; Martin C. Raff