English: Schematics illustrating comparable developmental processes in protistan holozoans versus animals. (A,B) Ichthyosporean Sphaeroforma arctica multinucleate cellularisation, which is controlled by the coordinated assembly of an actomyosin network (A), as also occurs in the Drosophila syncytial blastoderm (B). (C,D) Apical actomyosin contractibility has a role in shaping the colony of the choanoflagellate Choanoeca flexa (C), a process that shows similarities to the apical constriction leading to invagination during animal gastrulation (D). Shape shifting in Choanoeca flexa reacts to light cues and is reversible, and one colony form favours feeding whereas the other favours swimming. The red ovals indicate the actomyosin rings responsible for constriction: unlike in animal epithelia, where apical constriction directly leads to inward folding, constriction of the apical actomyosin ring in Choanoeca leads to a change in collar morphology and outward bending.